Note: Descriptions are shown in the official language in which they were submitted.
WO 92!20677
PGT/US92l03940
HETEROCYCLIC CHIRAL LIGANDS AND METHOD
FOR CATALYTIC ASYMMETRIC
DIHYDROXYLATION OF OLEFINS
Background
05 In nature, the organic constituents of animals,
microorganisms and plants are made up of chiral
molecules, or molecules which exhibit handedness.
Enantiomers are stereoisomers or chiral molecules whose
configurations (arrangements of constituent atoms) are
i0 nonsuperimposed mirror images of each other; absolute
configurations at chiral centers are determined by a set
of rules by which a priority is assigned to each
substituent and are designated R and S. The physical
properties of enantiomers are identical, except for the
15 direction in which they rotate the plane of polarized
light: one enantiomer rotates plane-polarized light to
the right and the other enantiomer rotates it to the
left. However, the magnitude of the rotation caused by
each is the same.
WO 92/20677 PCT/US92/03940
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The chemical properties of enantiomers are also
identical, with the exception of their interactions with
optically active reagents. Optically active reagents
interact with enantiomers at different rates, resulting
05 in reaction rates which may vary greatly and, in some
cases, at such different rates that reaction with one
enantiomer or isomer does not occur. This is partic-
ularly evident in biological systems, in which stereo-
chemical specificity is the rule because enzymes (bio-
logical catalysts) and most of the substrates on which
they act are optically active.
A mixture which includes equal quantities of both
enantiomers is a racemate (or racemic modification). A
racemate is optically inactive, as a result of the fact
that the rotation of polarized light caused by a molecule
of one isomer is equal to and in the opposite direction
from the rotation caused by a molecule of its enantiomer.
Racemates, not optically active compounds, are the
products of most synthetic procedures. Because of the
identity of most physical characteristics of enantiomers,
they cannot be separated by such commonly used methods as
fractional distillation (because they have identical
boiling points), fractional crystallization (because they
are equally soluble in a solvent, unless it is optically
active) and chromatography (because they are held equally
tightly on a given adsorbent, unless it is optically
active). As a result, resolution of a racemic mixture
into enantiomers is not easily accomplished and can be
costly and time consuming.
Recently, thEre has been growing interest in the
synthesis of chiral compounds because of the growing
demand for complex organic molecules of high optical
WO 92/20677 PCT/US92/03940
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purity, such as insect hormones and pheromones,
prostaglandins, antitumor compounds, and other drugs.
This is a particularly critical consideration, for
example, for drugs, because in living systems, it often
05 happens that one enantiomer functions effectively and the
other enantiomer has no biological activity and/or
interferes with the biological function of the first
enantiomer.
In nature, the enzyme catalyst involved in a given
chemical reaction ensures that the reaction proceeds
asymmetrically, producing only the correct enantiomer
(i.e., the enantiomer which is biologically or physio-
logically functional). This is not the case in labor-
atory synthesis, however, and, despite the interest in
and energy expended in developing methods by which
asymmetric production of a desired chiral molecule (e. g.,
of a selected enantiomer) can be carried out, there has
been only limited success.
In addition to resolving the desired molecule from a
racemate of the two enantiomers, it is possible, for
example, to produce selected asymmetric molecules by the
chiral pool or template method, in which the selected
asymmetric molecule is "built" from pre-existing,
naturally-occurring asymmetric molecules. Asymmetric
homogeneous hydrogenation and asymmetric epoxidation have
also been used to produce chiral molecules. Asymmetric
hydrogenation is seen as the first manmade reaction to
mimic naturally-occurring asymmetric reactions.
Sharpless, K.B., Chemistry-in_Britain, January 1986, pp
3g-44; Mosher, H.S. and J.D. Morrison, Science,
221:1013-1019 (1983); Maugh, T.H., Science, 221:351-354
WO 92/20677 PCT/US92/03940
V
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(1983); Stinson, S., Chemistry_andrEngineerin~-News,
_-:24 (6/2/86).
Presently-available methods of asymmetric synthesis
are limited in their applicability, however. Efficient
05 catalytic asymmetric synthesis reactions are very rare;
and they usually require a directing group and thus are
substrate limited. Because such reactions are rare and
chirality can be exceptionally important in drugs,
pheromones and other biologically functional
compositions, a catalytic method of asymmetric
dihydroxylation would be very valuable. In addition,
many naturally-occurring products are dihydroxylated or
can be easily derived from a corresponding vicinal diol
derivative.
Summar of the Invention
______Y_________________
Olefins or alkenes with or without proximal
heteroatom-containing functional groups, are asym-
metrically dihydroxylated, oxyaminated or diaminated
using an osmium-catalyzed process which is the subject of
the present invention. Chiral ligands which are novel
alkaloid derivatives, particularly dihydroquinidine
derivatives or dihydroquinine derivatives or salts
thereof, useful in the method of the present invention
are also the subject of the present invention.
20 Derivatives of the parent alkaloids, e.g. quinidine or
quinine, or salts thereof can also be used, but the rate
of catalysis is slightly slower.
In one embodiment of the present invention, the
chiral ligand is immobilized to or incorporated within a
polymer. Both monomeric and polymeric ligands can be
immobilized to or incorporated into the polymer. The
WO 92/20677 PGT/US92/03940
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immobilized or incorporated ligands form a complex with
the osmium catalyst during the reaction, resulting in
efficient catalysis in which the complex can be preserved
after the reaction, allowing repetitive use of the
05 complex. Alternatively, a preformed osmium-ligand
complex can be used in the reaction, and recovered.
In the method of asymmetric modification or addition
of the present invention, an olefin, a selected chiral
ligand, an organic solvent, water, an oxidant, an osmium
source and, optionally, an additive which accelerates
hydrolysis of the osmate intermediate are combined, under
conditions appropriate for reaction to occur. The method
of ligand-accelerated catalysis of the present invention
is useful to effect asymmetric dihydroxylation,
asymmetric oxyamination and asymmetric diamination of an
olefin of interest. A particular advantage of the
catalytic asymmetric method is that only small quantities
of osmium catalyst are required.
Brief Descri tion of the Drawin s
_________ _P__________________g_
Figure 1 is a schematic representation of asymmetric
dihydroxylation via ligand-accelerated catalysis which is
carried out by the method of the present invention.
Figure 2 is a schematic representation of asymmetric
catalytic oxyamination of stilbene which is carried out
by the method of the present invention.
Figure 3 is a plot of amine concentration vs second-
order-rate constant k for the catalytic cis-dihydroxy-
lation of styrene. At point a, no amine has been added.
Point a thus represents the rate of the catalytic process
in the absence of added amine ligands. Line b represents
the rate of the catalytic process in the presence or
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varying amounts of quinuclidine, a ligand which sub-
stantially retards catalysis. Line c represents the rate
of the catalytic process in the presence of the di-
hydroquinidine benzoate derivative 1 represented in
05 Figure 1. K is defined as Kobs/[Os04]o where rate
-d[styrenej/dt ~-4obs [styrene]. Conditions: 25°C,
[Os04]o - 4 x 10 M, [NMO]o - 0.2M [styrene]o ~ O.1M.
Figure 4 is a schematic representation of a proposed
mechanism of catalytic olefin dihydroxylation. This
scheme shows two diol-producing cycles believed to be
involved in the ligand-accelerated catalysis of the
present invention. Formula 1 represents an alkaloid-
osmium complex; formula 2 represents a monoglycolate
ester; formula 3 represents an osmium(VIII)triox-
oglycolate complex; formula 4 represents a bisglycolate
osmium ester; and formula 5 represents a
dioxobisglycolate.
Detailed_Description_of_the,Invention
Asymmetric epoxidation has been the subject of much
research for more than ten years. Earlier work demon-
strated that the titanium-tartrate epoxidation catalyst
is actually a complex mixture of epoxidation catalysts in
dynamic equilibrium with each other and that the main
species present (i.e., the 2:2 structure) is the best
catalyst (i.e., about six times more active than titanium
isopropoxide bearing no tartrate). This work also showed
that this rate advantage is essential to the method's
success because it ensures that the catalysis is chan-
neled through a chiral ligand-bearing species.
The reaction of osmium tetroxide (0s04) with olefins
is a highly selective and reliable organic transforma-
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"' ~ ~ ~ '~! ~ ,..
-7-
Lion. It has long been known that this reaction is
accelerated by nucleophilic ligands. Criegee, R. Justus
Liebi s Ann. Chem., 522:75 (1936); Criegee, R. et al.,
_____~____________ ___
Justus-Liebigs-Anrt__Chem-, 550:99 (1942); VanRheenen et
05 al., Tetrahedron Lett., 1973 (1976). It has now been
shown that a highly effective osmium-catalyzed process
can be used to replace previously known methods, such as
the stoichiometric asymmetric osmylation method.
Hentges, S.G. and K.B. Sharpless, Journal__of-the
American_Chemical_Society, 102:4263 (1980). The method
of the present invention results in asymmetric induction
and enhancement of reaction rate by binding of a selected
ligand. Through the use of the ligand-accelerated
catalytic method of the present invention, asymmetric
dihydroxylation, asymmetric diamination or asymmetric
oxyamination can be effected.
As a result of this method, two hydroxyl groups are
stereospecifically introduced into (imbedded in) a
hydrocarbon framework, resulting in cis vicinal di-
hydroxylation. The new catalytic method of the present
invention achieves substantially improved rates and
turnover numbers (when compared with previously-available
methods), as well as useful levels of asymmetric induc-
tion. In addition, because of the improved reaction
rates and turnover numbers, less osmium catalyst is
needed in the method of the present invention than in
previously-known methods. As a result, the expense and
the possible toxicity problem associated with previously-
known methods are reduced. Furthermore, the invention
allows the recovery and reuse of osmium, which reduces
the cost of the process.
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The method of the present invention is exemplified
below with particular reference to its use in the asym-
metric dihydroxylation of E-stilbene (C6H5CH:CHC6H5) and
traps-3-hexene (CH3CH2CH:CHCH2CH3). The method can be
05 generally described as presented below and that descrip-
tion and subsequent exemplification not only demonstrate
the dramatic and unexpected results of ligand-accelerated
catalysis, but also make evident the simplicity and
effectiveness of the method.
The asymmetric dihydroxylation method of the present
invention is represented by the scheme illustrated in
Figure 1. According to the method of the present in-
vention, asymmetric dihydroxylation of a selected olefin
is effected as a result of ligand-accelerated catalysis.
That is, according to the method, a selected olefin is
combined, under appropriate conditions, with a selected
chiral ligand (which in general will be a chiral sub-
stituted quinuclidine), an organic solvent, water, an
oxidant and osmium tetroxide and, optionally, a compound
which promotes hydrolysis of the products from the
osmium. Acids or bases can be used for this purpose. In
one embodiment, a selected olefin, a chiral ligand, an
organic solvent, water and an oxidant are combined; after
the olefin and other components are combined, Os04 is
added. The resulting combination is maintained under
conditions (e. g., temperature, agitation, etc.) conducive
for dihydroxylation of the olefin to occur. Alter-
natively, the olefin, organic solvent, chiral ligand,
water and Os04 are combined and the oxidant added to the
resulting combination. These additions can occur very
close in time (i.e., sequentially or simultaneously).
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In one embodiment of the present invention,
components of the reaction mixture are combined, to form
an initial reaction combination, and olefin is added
slowly to it, generally with frequent or constant agi-
05 tation, such as stirring. In this embodiment, designated
the "slow addition" method, organic solvent, chiral
ligand, water, Os04 and the oxidant are combined. The
olefin can then be slowly added to the other reactants.
It is important that agitation, preferably stirring, be
applied during the olefin addition. Surprisingly, for
many, if not most olefins, slow addition of the olefin to
the initial combination results in much better enantio-
meric excess (ee), and a faster rate of reaction than the
above-described method (i.e., that in which all the
olefin is present at the beginning of the reaction). The
beneficial effects (i.e., higher ee's) of slow olefin
addition are shown in Table 5 (Column 6). A particular
advantage of this slow-addition method is that the scope
of the types of olefins to which the asymmetric
dihydroxylation method can be applied is greatly
broadened. That is, it can be applied to simple
hydrocarbon olefins bearing no aromatic substituents, or
other functional groups. In this process, the olefin is
added slowly ;(e.g., over time), as necessary to maximize
ee. This method is particularly valuable because it
results in higher ee's and faster reaction times.
In another embodiment of the present method, the
chiral ligands are immobilized or incorporated into a
polymer, thereby immobilizing the ligands. Both monomers
and polymers of alkaloid ligands can be immobilized. The
immobilized ligands form a complex with the osmium
catalyst, which results in formation of an osmium
WO 92/20677 PCT/US92/03940
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catalyst complex which can be recovered after the
reaction. The Os04-polymer complex is recoverable and
can be used for iterative processes Without washing or
other treatment. The complex can be recovered, for
example, by filtration or centrifugation. By employing
05 alkaloid derivatives, heterogeneous catalytic asymmetric
dihydroxylation is achieved with good to excellent
enantioselectivities in the dihydroxylation of olefins.
Alternatively, alkaloid polymers can be used as
ligands. Alkaloid polymers which can be used are des-
cribed, for example, by Kobayashi and Iwai in Tetrahedron
Letters, 21:2167-?170 (1980) and Polymer_Journal,
13S3Z:263-271 (1981); by vonHermann and Wynberg in
Helvetica-Chimica_Acta, 60:2208-2212 (1977); and by Hodge
et al., J--Chem.-Soc._Perkin_Trans._I, (1983) pp. 2205-
2209. Both alkaloid polymer ligands and immobilized
ligands form a complex with the osmium in situ. The term
"polymeric", as used herein is meant to include monomers
or polymers of alkaloid ligands which are chemically
bonded or attached to a polymer carrier, such that the
ligand remains attached under the conditions of the
reaction, or ligands which are copolymerized with one or
more monomers (e. g., acrylonitrile) to form a co-polymer
in which the alkaloid is incorporated into the polymer,
or alkaloid polymers as described above, which are not
immobilized or copolymerized with another polymer or
other carrier.
Industrial scale syntheses of optically active
vicinal diols are possible using polymeric ligands. The
convenience and economy of the process is enhsnced by
recycling the alkaloid-Os04 complex. This embodiment of
the present method allows efficient heterogeneous
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asymmetric dihydroxylation utilizing polymeric or
immobilized cinchona alkaloid derivatives.
Polymeric cinchona alkaloids which are useful in the
present method can be prepared by art-recognized tech-
05 niques. See, for example, Grubhofer and Schleith,
Naturwissenschaften, 40:508 (1953); Yamauchi et al.,
Bull.-Chem._Soc.-Jpn_, 44:3186 (1971); Yamauchi et al.,
J. Macromal. Sci. Chem., A10:981 (1976). A number of
different types of polymers that incorporate dihydro-
quinidine or dihydroquinine derivatives can be used in
this process. These polymers include: (a) co-polymers
of cinchona alkaloid derivatives with co-polymerizing
reagents, such as vinyl chloride, styrene, acrylamide,
acrylonitrile, or acrylic or methacrylic acid esters; (b)
cross-linked polymers of cinchona alkaloid derivatives
with cross-linking reagents, such as 1,4-divinylbenzene,
ethylene glycol bismethacrylate; and (c) cinchona
alkaloid derivatives covalently linked to polysiloxanes.
The connecting point of the polymer backbone to the
alkaloid derivative can be at C(10), C(11), C(9)-O,N(1'),
or C(6')-0 as shown below for both quinidine and quinine
derivatives. Table 3 shows the examples of the monomeric
alkaloid derivatives which can be incorporated in the
polymer system.
For example, a polymer binding dihydroquinidine was
prepared by copolymerizing 9-(10-undecenoyl)dihydro-
quinidine in the presence of acrylonitrile (5 eq); a 13$
yield was obtained exhibiting 4~ alkaloid incorporation.
This polymer, an acrylonitrile co-polymer of 9-(10-
undecenoyl)-10,11-dihydroquinidine, is shown as polymer 4
in Table 1, below. Three other polymers, an acrylonitrile
co-polymer of 9-(4-chlorobenzoyloxy)quinine, (polymer 1,
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Table 3) an acrylonitrile co-polymer of 11-[2-
acryloyloxy)ethylsulfinyl]-9-(4-chlorobenzoyloxy)--
10,11-dihydroquinine (polymer 2, Table 1) and an acrylo-
nitrile co-polymer of 11-[2-acryloyloxy)-ethylsulfonyl]-
059-(N,N-dimethylcarbamoyl)-10,11-dihydroquinidine,
(polymer 3, Table 1) were prepared according to the
procedures of Inaguki et al., or slightly modified
versions of this procedure. See, Inaguki et al., Bull.
Chem._Soc._Jpn_, 60:4121 (1987). Using these polymers,
the asymmetric dihydroxylation of trans-stilbene was
carried out. The results are summarized in Table 1.
Good to excellent asymmetric induction and reasonable
reaction rates were observed. As shown in Table 1,
reaction with polymer 2 exhibited the highest degree of
asymmetric induction. The activity of the Os04-polymer
complex is preserved after the reaction, thus allowing
repetitive use of the complex. This reaction can be
carried out with terminal and aliphatically substituted
olefins to show good yields and enantioselectivities (for
example, styrene with polymer 2, 60~ ee, 68$ yield, and
ethyltrans-2-octenoate with polymer 3, 60~ ee, 858 yield)
and the same process can be applied to a variety of
different olefins.
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Table 1. Heterogeneous Catalytic Asymmetric
Dihydroxylation of trans-Stilbene Using Various Polymeric
Alkaloids
alkaloid polymer (025 eq), cat OsQ
secondary oxtdanl, solvent'
OH
- Secondary Reaction Reaction
05 Entry Polymers O:O' Oxidant Temp Time Yip>id (%) ee (%)
1 1 I mot% NMO rt 7d 6B -
2 ~ I mol% NMO 10 'C Z 3d 8187 8S93b
3 Z 1 mol9i, NMO rt 24 h 81 82
4 i -~ NMO rt 36 h 75 78
S s 1 mol% NMO 0 ~C 48 h 85 80
6 3 1.25 mol%K3Fe(CNk rt 18 h 96 87
7 1 mol% NMO 10 ~C ~8 h E7 82
8 1 LZS mol% I(sFe(t?J)<rt 48 h 91 86
aGeneral procedure is set out in detail in Example 14.
With N-methylmorpholine-N-oxide (NMO) acetone/water
(10/1, v/v) was the solvent and ferricyanide te~t-butyl
alcohol/water (1/1, v/v) was used as solvent. Results
vary slightly depending on different batches of polymer
2. cReaction was carried out with polymer 2 which had
20been used in entry 3 without further addition of Os04.
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'~~~'~~3~
In another embodiment of the present method, an
additive which accelerates hydrolysis of the osmate ester
intermediates can, optionally, be added to the reaction
combination. These additives can be acids or bases, for
05example. Bases are preferred for this purpose. For
example, soluble, carboxylic acid salts With organic-
solubilizing counter-ions (e. g., tetraalkyl ammonium
ions) are useful. Carboxylate salts which are preferred
in the present reaction are soluble in organic media and
loin organic/aqueous co-solvent systems. For example,
tetraethyl ammonium acetate has been shown to enhance the
reaction rate and ee of some olefins (Table 5). The
additive does not replace the alkaloid in the reaction.
Compounds which can be used include benzyltrimethyl-
l5ammoniumacetate, tetramethylammonium acetate and
tetraethylammonium acetate. However, other oxyanion
compounds (e.g., sulfonates, carbonates, borates or
phosphates) may also be useful in hydrolyzing the osmate
ester intermediates. The compound can be added to the
ZOreaction combination of organic solvent, chiral ligand,
water and Os04 in a reaction vessel, before olefin
addition. It is important to agitate (e. g., by stirring)
the reaction combination during olefin addition. The
additive can also be added to the reaction combination,
25 described above, wherein all of the olefin is added at
the beginning of the reaction. In one embodiment, the
amount of additive is generally approximately 2 equiva-
lents; in general from about 1 to about 4 equivalents
will be used.
30 In another embodiment of the present invention, the
process can be run in an organic non-polar solvent such
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as toluene. This embodiment is particularly useful in
the slow addition method.. Preferably, a carboxylate
compound which accelerates hydrolysis of the osmate ester
intermediates (e. g., tetraethyl- or tetramethyl ammonium
05 acetate) is added. This embodiment is designated the
"phase transfer" method. In this embodiment olefins
which are not soluble, or have limited solubility, in
mixtures of acetone/water or acetonitrile/water, are
dissolved in toluene arid then added slowly a mixture of
organic solvent, chiral ligand, water and Os04. The
carboxylate salt serves the dual function of solubilizing
the acetate ion in the organic phase where it can promote
hydrolysis of the osmate ester, and carrying water
associated with it into the organic phase, which is
essential for hydrolysis. Higher ee's are obtained with
many substrates using this method.
In a further embodiment of the present invention, a
boric acid or a boric acid derivative (R-B(OH)2, Rlalkyl,
aryl or OH), such as boric acid itself (i.e., B(OH)3) or
phenylboric acid (i.e., Ph-B(OH)2), can be added to the
reaction mixture. In the slow addition method, the boric
acid is added to the ligand - organic solvent - Os04
mixture prior to the addition of the olefin. The amount
of boric acid added is an amount sufficient to form the
borate ester of the diol produced in the reaction.
Without wishing to be bound by theory, it is believed
that the boric acid hydrolyzes the osmium ester and
captures 'the diols which are generated in the reaction.
Neither water nor a soluble carboxylate such as tetra-
alkyl ammonium carboxylate, is required to hydrolyze the
osmium ester in the present reactions. Because the
presence of water can make the isolation and recovery o~
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water-soluble diols difficult, the addition of a boric
acid makes isolation of these diols easier. Especially,
in the case of an aryl or alkyl boric acid, it is easy
because, in place of the diol, the product is the cyclic
05borate ester which can be subsequently hydrolyzed to the
diol. Iwasawa et al., Chemistry_Letters, pp. 1721-1724
(1988). The addition of a boric acid is particularly
useful in the slow addition method.
In another embodiment of the present method,
l0oxidants such as potassium hexacyanoferrate (III)
(potassium ferricyanide, K3Fe(CN)6) is added to the
reaction as a reoxidant. In a preferred embodiment, at
least two equivalents of the oxidant (based on the amount
of olefin substrate) is added to the reaction. It is
l5also preferable that an equivalent amount of a base, such
as potassium carbonate (K2C03), is added in conjunction
with the reoxidant. High enantioselectivities are
obtained in catalytic asymmetric dihydroxylations using
K3Fe(CN)6 as the reoxidant.
2p The use of potassium ferricyanide in a stoichio-
metric amount as an oxidant for non-asymmetric osmium-
catalyzed dihydroxylation of olefins.was reported by
Minato, Yamamoto and Tsuji, in J._Org__Chem-, 55:766
(1990). The addition of K3Fe(CN)6 (in conjunction with
25the base) results in an improvement in the ability of the
Tsuji's catalytic system to turn over, even in the
presence of quj.nuclidine, a ligand which strongly
inhibits catalysis when other oxidants are used, e.g.
N-methylmorpholine-N-oxide (NMO). In the present
30embodiment, potassium ferricyanide and potassium
carbonate were added to the present cinchona alkaloid-
based asymmetric dihydroaylation process and the outcome,
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was unexpected (i.e. not just another way to reoxidize
the osmium and/or achieve better turnover with difficult
substrates). As shown in Table 2, the use of potassium
ferricyanide/potassium carbonate in place of NMO leads to
OS across-the-board increases in the level of asymmetric
induction for most olefins. The first two columns of
data shown in Table 2 are for results employing NMO with
and without "slow addition" of olefin, respectively. The
third column reveals the results obtained using K3Fe(CN)6
with the same substrates and without "slow addition" of
the olefin. The improvements of enantioselectivity are
great as evidenced by the fact that the previous results
(shown in Table 2) were obtained at O°C while the
ferricyanide experiments were performed at room
temperature. The ferricyanide reactions can be run at a
range of temperatures, however, depending.upon the
substrate.
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Table 2. Percentage enantiomeric excesses of diols
obtained in the asymmetric dihydroxylation of olefins
under different catalytic conditions using
dihydroquinidine p-chlorobenzoate as the chiral ligand.
OH
R ~ R. -.----~. R R.
05
OH
NMOa K3Fe(CN)66
entry olefins ee(~) ee(%) ee(%)
(slow addition) (no slow addition) (no slow addition)
I , 60 56 73
2 ' ~ ~ I 95 78 99
I~
3 ~ 86 65 91
4 ~ \ ~~ 79 76 91
w COilNe
5 I ~ 86 60 95
w 69 20 74
aReacti$ns were carried out in acetone-water, 10:1 v/v,
at 0°C. Reactions were carried out in tert-butyl
alcohol-water 1:1 v/v, at ambient temperature. In all
cases the isolated yield was 85$-95$
The amount of water added to the reaction mixture is
an important factor in the present method, The optimum
amount of water to be added can be determined empirically
and, in general, should be that amount which results in
maximum ee. Generally, approximately 10 to 16
equivalents of water can be added, preferably 13 to 14
equivalents should be used.
An olefin of interest can undergo asymmetric
dihydroxylation according to the present invention. For
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example, any hydrocarbon containing at least one carbon-
carbon double bond as a functional group can be asym-
metrically dihydroxylated according to the subject
method. The method is applicable to any olefin of
05 interest and is particularly well suited to effecting
asymmetric dihydroxylation of prochiral olefins (i.e.,
olefins which can be converted to products exhibiting
chirality or handedness). In the case in which the
method of the present invention is used to asymmetrically
dihydroxylate a chiral olefin, one enantiomer will be
more reactive than the other. As a result, it is pos-
sible to separate or kinetically resolve the enantio-
morphs. That is, through use of appropriately-selected
reactants, it is possible to separate the asymmetrically
dihydroxylated product from the unreacted starting
material and both the product and the recovered starting
material will be enantiomerically enriched.
The chiral ligand used in the asymmetric dihydroxyl-
ation method will generally be an alkaloid, or a basic
nitrogenous organic compound, which is generally
heterocyclic. The chiral ligand can be a naturally
occurring compound, a purely synthetic compound or a salt
thereof, such as a hydrochloride salt. The optimum
derivative which is used can be determined based upon the
Process conditions for each reaction. Examples of
alkaloids which can be used as the chiral ligand in the
asymmetric dihydroxylation method include cinchona
alkaloids, such as quinine, quinidine, cinchonine, and
cinchonidine. Examples of alkaloid derivatives useful in
the method of the present invention are shown in Table 3.
As described in detail below, the two cinchona alkaloids
quinine and quinidine act more like enantiomers than lake
diastereomers in the scheme represented in Figure 1.
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As represented in Figure 1, and as shown by the
results in Table 4, dihydroquinidine derivatives (repre-
sented as DHQD) and dihydroquinine derivatives (repre-
sented as DHQ) have a pseudo-enantiomeric relationship in
the present method (DHQD and DHQ are actually diastereo-
05 mers). That is, they exhibit opposite enantiofacial
selection. Such derivatives can be, for example, esters
or ethers, although other forms can be used. The choice
of derivative depends upon the process. When dihydro-
quinidine is used as the ligand, delivery of the two
hydroxyl groups takes place from the top or upper face
(as represented in Figure 1) of the olefin which is being
dihydroxylated. That is, in this case direct attack of
the re- or re,re- face occurs. In contrast, when the
dihydroquinine derivative is the ligand used, the two
hydroxyl groups are delivered from the bottom or lower
(si- or si,si-face) face of the olefin, again as repre-
sented in Figure 1. This is best illustrated by
reference to entries 1, 2 and S of Table 4. As shown,
when DHQD (dihydroquinidine esters) is used, the re-
sulting diol has an R or R,R configuration and when
ligand 2 (dihydroquinine esters) is used, the resulting
diol has an S or S,S configuration.
pCT/US92103940
WO 92/20677
~.~.
~~~'~
-21_
Table .3 Alkaloid Derivatives
Ph ~ R Ph
_"r' R
Ph Ph OH
H O''R
~O
g Dihydroquinidine held (~) 96ee
~
Derivative
3-C1C~ 3-chlorobenzoyl 89
os
2-methoxybenzoyl 89
~.M 3-methoxybenzoyl 87 96.?
2-C10H7 2-t~apthoyl 95.4 98.6
C~'lil cyclohexanoyl 90 91
4~PhC6Fi~ 4-pheaylbenzoyl 89
2,6-Q~ieO)2C6H3 l thoxy 88 92
~
y
,~M 4-methoxyenzoyl 91 97.6
4-C1C~';t 4-chlorobenzqyl 93 99
2-C3C~ 2-chlorobenzoyl 87 94.4
l 5 ~NOZC6Ht 4-nitrobenzoyl ?1 93
~"i5 bettzoyl 92 98
WO 92/20677 PCT/US92/03940
-22-
Table 3 cont.
MeZN dimethyl- 96 95
carbamoyl
Me acetyl ?2 94
MeOCHI a-methoxyacetyl 66 93
05 AcOC'HZ a-acetoxyacetyl 96 825
Me3C trimethylacetyl 89 86.5
?he example below is a phospharyl derivative and therefore differs from the
carboxylic add ester derivatives shown above: the phosphorus atom is directly
bound to the oxygen atom of the alkaloid.
1o ph2p~p~ diphenylphosphinic 69 97.5
ester
WO 92/20677 PCT/US92/03940
-23-
Table 4
iigand; ee';
Olefins conign. of dlol
OHCD; 20x, (70x, 10h); RR
DHO; (60'.G, l6hj; SS
~n-Bu OHOD; (70'.G, 120h)
05 ~~Bu
OHCD; (69'x., 30h); RR
~~-CSHn DHC; (63'x., 30h); SS
OHOD; 12'.G, (46'.(i, 24h),
(76'.6, 24h ~ 1 eq OAc)
OHCO; 3T.5'.G
DHOD; (46'~G, 24h, ttj
~ DHCD; (40x, 24h, rt)
cHCD; 46x, (so~,c, sohj; a
DHGD; sox
oHOO; sox
Ci~Cf DHOD; 35x, (40X, 12h)
° Enantiomeric excesses in parentheses were obtained w~h slow addition
of olefin over a period of time
ihdrcated and with stirri~ at 0°C except otherwise stated.
Tetraethylammonium acetate tetrahydrate
were added in some cases as indicated.
WO 92/20677 PCT/US92/03940
~Q~'~~3~
Table 4 cont.
ligand; ee';
Olefins confgn. of dioi
OHOD; 56%, (61x,, Sh); R
OHC; 54~~G; S
05 ~ ~ ~ OHOD; 53~~G
DHOD; 65~.G
DHCD; 63~.4
OHOD; 85%, (86~x., Sh); RR
DHO; 55'.G, (80~.G, Sh); SS
DHCO; 0~10~.~
OHOD; 33%; R
OHGD; 34X, (53%, Z4h)
DHt?D; ist%
DHGD; 6T%
Me0 /
' l.riarttbmeric excesses in parentheses were obtained with sbw add~ion of
olefin over a perbd of time
~i~~ and with stirrir~ at O°C except otherwise stated.
Teiraethylammoruum acetate tetrahydrate
were added in some cases as Indicated.
WO 92/20677 PCT/US92/03940
-25-
Table 4 cont
ligand; ee';
Olefins confgn. of diol
DHOD; '0°~G
O
DHOD; 80°.G; 92°~G In the presence of 2 eq. OAC; RR
05 , ~ ~ ' ~ DHD; 79'.x; SS
DHQD; 10'/e, (78%, 26h),
(81°~, 16h f leq OAc)
OHD; (73°.6, 26h)
OAc OHOD; 76°~G; RR
OCOPh DHGD; 80°/.
CI OHCD; 50'.G, (78°/., 10h) .
I / OHOD; ~0°.G
/ _ . DHQD; (~d%, 10h)
OH00; 34%
O
DHOD; 2T%
' Enantiomeric excesses in parentheses were obtained with slow addition of
olefin over s period of time
~,~~ ~ wlth stirrir~ at O°C except otherwise stated. Tetraethytammonium
acetate teuahydrase
were added in some cases as indicated.
WO 92/20677 PCT/US92/03940
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Table 4 cont
Olefins ligand; ee';
ysH,yCO~Me OHQD; 38°.G
~COyEt OHOD; 47.d°.6, (67°.(~, 3th)
~SHn
05 . ~C02Et DHOO; 53°~L
Et ~C~CH2Ph DHOD; 45°.G
Et~
O
O \ COZMe DHOD; (52'.f. de, 31 h)
\ C02Me ONOD; (7Q~.f, de, d2h)
O .~'
COZEt OHCD; 7d.3X
C02Me OHOD; (36°.G, 2dh + OAC, n)
_O
OEt OHaD; 92°.G
O
OHQD; 9tX
/
~ ~2~2Ph DHOD; 80~85X
O
OMe DHOD; s50X, (80X, slow addltlonj
I~AeO . O
DHOD; (38X, toluene-water, 2dh +~OAc, h)
a Enarriiomeric excesses in parentheses were obtained with sbw addition of
olefin over a period of time
indicated and wah stirring at O°C except otherwise stated.
Tetraethylammonium acetate tetrahydrate
were added tn some cases as indicated.
WO 92/20677 PCT/US92/03940
_..
_2,_
Table 4 cont
Olefins ligand; ee';
OHGD; (10°.G, 2dh, rt)
~O
DHCO; (36°.G, 2dh + OAc, rtj
O
OHQD; (37°.G, 12h f OACj
~~~J
OEt
_ 1 OHCD; 2T~G, (31'6, 13h)
05 ~OEt
~7Hs5~0 OHGD; (56°.G, 20h)
(66.G, 20h ~ OAc)
Me
DHDD; (~6%, l8hj
(SO°.G, 18h ~ OACj
OMe
' \~ home OHOD; (75°.G, l8hj
(83X, 18h ~ OAcj
Me
' ' pOJ DHCD; (80°A, 10h)
/ (89°~G, 10h ~ OAc j
Ph
DHCD; (85%, 20h)
~ / \ O J (8T%, 20h f OAC)
DHGD; (2T%, 23h t OACj
OS8Ae3
DHGD; (72%, 23h)
(78'~G, 23h ~ OAcj
' ~nanlameric excesses tn parentheses were obtained with slow addition of
olefin over a period of time
indicated and w'dh stirring at O°C except otherwise stated
Tetraethytammonium acetate tetrahydrate
were added in some cases as indicated.
WO 92/20677 PCT/US92103940
-2&-
Table 5
Fsuntiomeric exot~ses obtained in the asyatmetric d~ydroxylation of
oleFms under different conditions
ntalytic~ catalytic catalyhc'~
entry olefin stoich3ometric'a (original) (acetate) (slow addition)
05 1 ~ 61 56 61 60 (5 h)
2 ~ 87 65 T3 86 (5h)
.t
3 ~ T9 8r 52 78 (26 h)!
4 ~ 80 128 61 4b (24 h)~
76 (24 h + OAc~
~ 69 20 64 70 (10 h)
sM stoichioaxtric reactions were carried oyt i:~ ac~etane-water, 10:1 ~/~, at
0 'C and at a
conantntion of O.ls M In each reagent. ~AIi enctioru was serried out at 0'C
according to the
origisul procedure reported in rd. 1(a). cAD tvctions went carried ont exsctly
ss desrrsbed in ref.
Ira) 0.c. without slow addition) except that ~ eq of E4 NOAc~~HZO were p~sa~t.
~AII ructions
were auried out at 0 'C as desas'bed in note Z !or hags-~hexene with an
alkaloid oonoertation of
0 25 M. The period for slow addition of the olefin b indicted in parmthnes.
The ee's shown in the
?able wen obtained with dihydroquinidine ~robenzoate as the ligand. Under the
same
mnditioru, the pseudoenantiomer, dihydroqvinitwe p.d~lorobes>zoate, provides
products with ee's 5-
10~ bwer. In aD uses the isolated yield was >s5-93'1. ~Ihis reaction took 7
days to complete. lWith
as addition period of 16 h K's of 63 and a5'1. were obtained at 0'C and 2Q'C,
ttspecdvely; with
the mmbanation oI slow addition ova a persod of 16 h and the pnnsnoe of 1 eq
of Et4NOANHZO at
Q°C, an at of ale was raalfsed. t!'Ihts loot s days to ot~pkte. ~ the
reaction was
carried out at 20 °C and the cle5n was added ova a period of Z4 4, an a
of s9'~ was obtained.
WO 92/20677 ~ ~ ~ ~ ~ ~ ~ PGT/US92/03940
-29-
Because of this face selection rule or phenomenon,
it is possible, through use of the present method and the
appropriate chiral ligand, to pre-determine the absolute
configuration of the dihydroxylation product.
05 As is also evident in Table 4, asymmetric di-
hydroxylation of a wide variety of olefins has been
successfully carried out by means of the present in-
vention. Each of the embodiments described results in
asymmetric dihydroxylation, and the "slow addition"
method is particularly useful for this purpose. In each
of the cases represented in the Table in which absolute
configuration was established, the face selection "rule"
(as interpreted with reference to the orientation
represented in Figure 1) applied: use of DHQD resulted
in attack or dihydroxylation occurring from the top or
upper face and use of DHQ resulted in attack or
dihydroxylation occurring from the bottom or lower face
of the olefin. This resulted, respectively, in formation
of products having an R or R,R configuration and products
having an S or S,S configuration.
In a preferred embodiment of the present method,
aromatic ethers of various cinchona alkaloids are used as
ligands. The term "aromatic ethers" includes aryl ethers
and heterocyclic ethers. A high level of asymmetric
induction can be obtained using aromatic ethers of
dihydroquinidine or dihydroquinine as ligands. For
example, aromatic ethers having the following formula are
particularly useful:
WO 92/20677 PCT/US92/03940
-30-
wherein R is phenyl, naphthyl, or o-methoxyphenyl. The
stoichiometric asymmetric dihydroxylation of various
dialkyl substituted olefins was performed using the
phenyl ether derivative of dihydroquinidine. The results
05 are shown in Table 6.
Table 6. Stoichiometric Asymmetric Dihydroxylation
Phenyl Ether Dihydroquinidine
1) leq OsO~ OH
RZ lcq 1, in toluene RZ
Z) LiAIH, J Ri
OH
Entry O)efins Reaction temp l6ee' 'J6ee' with 3
«) (for compuison)
1 0 85 7I
Z ~78 9~
0 88 T3
-78 93
0 89 79
6 _ - ~78 94
a
COOEt 0 90 67
a
O . COOMe 0
8
O
aEnantiomeric excess was determined by GLC or H~LC
analysis of the bis-Mosher ester derivatives. The
reaction was worked up with NaHS03 in H20-THF.
Diastereomeric excess.
The reaction was performed by adding 1 eq of olefin
to a 1.1 mixture of Os04 and the ligand in dry toluene
(0.1M) followed by a reductive work-up using lithium
aluminum hydride (LiAlH4) to yield the (R,R)-diol in
WO 92/20677 PCT/US92/03940
-31-
60-95~ yield with good to excellent enantiomeric excess.
Reactions with a,~-unsaturated esters also proceeded with
much improved enantio- and diastereoselectivities (>_90$,
as shown in entries 7 and 8, Table 6) using this ligand.
05 gy lowering the reaction temperature to -78°C, the
reaction with straight chain dialkyl substituted olefins
proceeded with very high enantioselectivities (>_93$, as
shown in entries 2, 4 and 6 of Table 6). In the several
cases which were plotted the variance in ee with temper-
ature closely followed the Arrhenius relationship.
Several dihydroquinidine aromatic ether derivatives
were examined as chiral ligands for the asymmetric
dihydroxylation of (E)-3-hexene, as shown in Table 7,
below. Reactions with all of the aromatic ether
derivatives tried exhibited higher enantioselectivities
than the corresponding reaction with p-chlorobenzoate
dihydroquinidine. The highest enantioselectivity was
obtained with 9-0-(2'-methoxyphenyl)-dihydroquinidine
(entry 2, Table 7).
WO 92/20677 PCT/US92/03940
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Table 7. Stoichiometric Asymmetric Hydroxylation of
(E)-3-hexene
1)Ieq
RO~, -''
1 Os0 OH
1 in toluene, 0'C
2)LAH OH
Entry 1 2 3 4 5
0 5 R \ .~' ~ / Meo \ l °~'~
OMe CF3
%ee 1 85 88 81 76 75
In one embodiment of the present method, aromatic
ether ligands were used in the catalytic asymmetric
dihydroxylation of (E)-3-hexene. In this embodiment, the
results are summarized in Table 8. The catalytic
asymmetric dihydroxylation reactions (entries 1-3, Table
8) were carried out by slow addition of (E)-3-hexene (1
eq) to a mixture of phenyl ether dihydroquinidine (0.25
eq), N-methylmorpholine N-oxide (NMO, 1.5 eq) and Os04
(0.004 eq) in acetone-water (10/1, v/v) at 0°C, followed
by work-up with Na2S205. The reaction proceeded faster
WO 92/20677 PCI"/US92/03940
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upon addition of tetraethylammonium acetate (2 eq) to the
reaction mixture (entry 4, Table 8). Potassium
ferricyanide was added as the secondary oxidant (entries
and 6, Table 8). In these cases, slow addition of
05 olefin was not required. To a mixture of (E)-3-hexane
(1 eq), aromatic ether of dihydroquinidine (0.25 eq),
K3Fe(CN)6 (3eq) and potassium carbonate (K2C03 3 eq) in
tent-butyl alcohol-water (1/1, v/v) was added Os04
(0.0125 eq); the resulting mixture was stirred at room
temperature for 20 hours. Reductive work-up (with
Na2S03) gave the diol in 85-90$ yield with essentially
the same ee as that obtained in the stoichiometric
reaction.
Table 8. Catalytic Asymmetric Dihydroxylation of
(E)-3-hexene
Entry Ligand Os04 Secondary Additive Reaction Reaction g'6ee
oxidant Temp ('C)Time (hr)
I 1 0.4aZOl~ NMO 0 16 70
2 1 0.4 NMO 0 30 75
3 1 0.4 NMO 0 120 85
4 1 0.4 NMO Et4NOAc 0 16 82
5 1 1.25 K3~(~6 K2CQ3 rt 20 83
6 2 1?S K3~(~6 K2C03 rt 20 89
WO 92/20677 PCT/US92/03940
~~l~r~~3~
-34-
Enantioselectivities in the dihydroxylation of dialkyl
substituted olefins, which were previously only possible
through the use of stoichiometric reagents at low
temperature, can now be obtained in the catalytic
OS asymmetric dihydroxylation using these aromatic ether
ligands at room temperature. Disclosed here are two
ligands which are particularly useful in the present
method: the 9-0-(9'phenanthryl) ethers and the
9-0-(4'-methyl-2'-quinolyl) ethers of dihydroquinidine
(la and 1b below) and dihydroquinine (2a and 2b below).
~ ~~ OH
OsCI, I K fo(CI~s
R' t-BuOH-HiJ _
OH
~ ~ CG3
1
o~
Et~ Et~
N
H H O-R
N
IArO
N N
. c ~3
i
R. ~ I ~_w ~ a l
w w N '' o
The R group can include other benzenoid hydrocarbons.
The aromatic moieties also can be modified by
substitutions such as by lower alkyl, alkoxy or halogen
radical groups.
WO 92/20677 PCT/US92/03940
-35-
Additional effective heterocyclic aromatic ligands
include:
/ N N H_ GN N~N
''""~''~~ N'/N
''''
The improvements achieved with these new ligands are
05 best appreciated through the results shown in Table 9. A
particularly important advantage is that the terminal
olefins (entries 1-7, Table 9), have moved into the
"useful" ee-range for the first time.
WO 92/20677 PCT/US92103940
-36-
Table 9. Ee ($)a of the Diols Resulting From Catalytic
Asymmetric Dihydroxylation
dass of ~ olefirf t~ , la 1b lc confi
f~'C Q~ OviE~ Q'CB) r~
oldie
1 ".GH~~ 0 74 65 45' R
05 Z crdo~,Hn~ O 93 85 64' (R)
3 EBu~ 0 79 79 44' R
R~~
4 pn'~ 0 78 87 74' R
0 83 93 88' R
6 ~ 0 82 ?3 3?' R
H
~
~
R~~ 7 ~ O I 69 D 74' (R)
WO
8 ".gu~"'ev rt 96 90 79 R,R
R~~R, g ".~Ht~a.~~~ 94 85 67 2$,3R
rt
10 ~,~~ rt 98 98 91 2S,3R
I1 ~~pn rt 99 98 ~ R,R
~ I2 pn~ rt 86 81 74 R
R~~~
I3 . ~~ rt 93 D 91 R,R
_ _ .
~nantiomeric excess as were determined~by HPLC, GC, or
H-NMR analysis of the bis-MTPA esters (see
supplementary materials for details of analyses). bAl1
reactions were performed essentially as described in
Example 20 with some variations: (1) 1-1.25 mol ~ Os04 or
WO 92/20677 PCT/US92/03940
.,w«.. ~ ~ ~ ~ ~f sy ..
-37-
K Os02(OH) ; (2) 2-25 mol.% ligand, (3) 0.067-0.10 M in
olefin; (4~' 18-24 h reaction time. In all cases the
isolated yield of the diol was 75-95%, cAll olefins are
commercially available except entries 6 and 7. The
05 absolute configurations of the diols were determined by
comparison of their optical rotations with literature
values (entries 1, 3-5, 8, 10-13), or with an authentic
diol (R)-(-)-2-phenyl-1,2-prq$anediol (entry 6), or by
comparison of ORD (entry 9). The remaining two
(entries 2,7) are tentatively assigned by analogy from
optical rotations of closely related diols and the
retention times of the bis MTPA esters on HPLC (see
supplementary material for details). eReaction was
carried out at room temperature.
The data for the new ligands la and 1b has been
compared to the results for another ligand, the p-chloro-
benzoate lc (last column of Table 9). Note further that
the highest enantioselectivities for each substrate have
been highlighted by bracketing, and that this bracketing
is conspicuously sparse in the column under ligand lc.
Clearly, ligands la and 1b also deliver a significant ee
enhancement for traps-substituted olefins, especially
those lacking aromatic substituents (entries 8 and 9).
The six possible substitution patterns for olefins
are:
R~~r R= R' R~ R~
R R~ RI R
moao~ gem..d1- cps-di- lranrdl- tr1- ~
Four of these classes are represented in Table 9.
The present success with the mono- and gem-dissbstituted
types has essentially doubled the scope of the catalytic
ADH when compared to diol production when ligands other.
than aromatic ether ligands are used.
WO 92/20677 PCT/US92/03940
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Strikingly absent from Table 9 are the results for
the dihydroquinine ligand analogs (i.e., 2a, 2b and 2c).
The quinidine and quinine analogs of these new ligands
also give very good results with the same olefin classes
05 shown in Table 9. Like the original p-chlorobenzoate
ligand comparison (lc vs 2c),2b the quinine ether series
gives somewhat lower ee's than their dihydroquinidine
counterparts (la vs 2a and 1b vs 2b). For example, vinyl
cyclooctane (entry 2) gives the S-diol in 8.8$ ee using
2a compared with the R-diol in 93$ ee recorded in Table 9
using la.
The detailed general procedure for the catalytic ADH
is given in note Example 20, using ligand la and vinyl
cyclooctane as the substrate. Note the experimental
simplicity of the process. I is performed in the
presence of air ar_d water at either ambient or ice bath
temperature. A further advantage is that the most
expensive component, the ligand, can be easily recovered
in >80$ yield.
Note also that the solid and nonvolatile osmium (VI)
salt, K20s02(OH)4, is used in place of osmium tetroxide.
This innovation should be useful in all catalytic
oxidations involving Os04 since it avoids the risk of
exposure to volatile osmium species.
Another olefin class can be asymmetrically
dihydroxylated when 0-carbamoyl-,p-chlorobenzoate- or 0-
phenanthrolene- substitutions of DHQD or DHQ ligands are
used in the method of the present invention. This class
is the cis-disubstituted type of olefin. Table 10 shows
the ee's and $ yields for a variety of substrates when
these ligands were used. Procedures for producing these
ligands and for carrying out the ADH are illustrated irk,
Examples 23 and 24.
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Table 10: Enantiomeric Excesses (ee's) Obtained for cis-
Olefins with Various Dihydroquinidine Ligands;
ee ($ yield)
Substrate:
'I
s Li and:
DMC-O-DHQD 20(68) 17(71 4(78) 4(66) 17(66)
)
MPC-O-DI-iQD 4b(8?J 0(54) b(100) 6(90) 49(47)
DPC-0-DHQD 44(85) 10(37) 0(100) 3(74) 44(75)
PCB-O~DHQD 35(92) 2(80) 19(83) 4(75) 24(63)
to P~1-O.DH D 22( ) 4(78) 37(89) 7(75) -23($6)
PhC-O-DHQD 17(86) 12(69) 14(84) 0(89) 10(8~J
where the ligands are ether linked substituents of DHQD
designated as dimethyl carbamoyl (DMC), methyl phenyl
carbomoyl (MPC), diphenylcarbamoyl (DPC),
15 p-chlorobenzoate (PCB), phenanthryl (PHN) and phenyl
carbomoyl (PhC).
The greatest ee's were obtained when
0-carbamoyl-DHQD ligands were employed which indicates
that this class of compound is an attractive ligand for
20 asymmetric dihydroxylation of the cis-disubstituted type
of olefin. These results also demonstrate that
reasonably good yields and ee's can be obtained for this
WO 92/20677 PCT/US92/03940
-40-
olefin class and that, now, five of the six classes of
olefins can successfully be asymmetrically
dihydroxylated.
In general, the concentration of the chiral ligand
05 used will range from approximately 0.001 M or less to 2.0
M. In one embodiment, exemplified below, the solution is
0.261M in alkaloid 1 (the dihydroquinidine derivative).
In one embodiment of the method, carried out at room
temperature, the concentrations of each alkaloid
represented in Figure 1 is at 0.25M. In this way, the
enantiomeric excess resulting under the conditions used
is maximized. The amount of chiral ligand necessary for
the method of the present invention can be varied as the
temperature at which the reaction occurs varies. For
example, it is possible to reduce the amount of alkaloid
(or other chiral ligand) used as the temperature at which
the reaction is carried out is changed. For example, if
it is carried out, using the dihydroquinidine derivative,
at 0°C, the alkaloid concentration can be 0.15M. In
another embodiment, carried out at OoC, the alkaloid
concentration was 0.0625M.
Many oxidants (i.e., essentially any source of
oxygen) can be used in the present method. For example,
amine oxides (e. g., trimethyl amine oxides), tent-butyl
hydroperoxide, hydrogen peroxide, and oxygen plus metal
catalysts (e. g., copper (Cu+-Cu++/02), platinum (Pt/02),
palladium (Pd/02) can be used. Alternatively, Na0C1
KI04, KBr03 or KC103 can be used. In one embodiment of
the invention, N-methylmorpholine N-oxide (NMO) is used
as the oxidant. NMO is available commercially (e. g.,
Aldrich Chemicals, 97$ NMO anhydrous, or as a 60$
WO 92/20677 PCT/US92/03940
-41-
solution in water). In addition, as stated above,
potassium ferricyanide can be used in lieu of the amine
oxide. Potassium ferricyanide is an efficient oxidant in
the present method.
OS Osmium will generally be provided in the method of
the present invention in the form of osmium tetroxide
(0s04) or potassium osmate VI dihydrate, although other
sources (e. g., osmium trichloride anhydrous, osmium
trichloride hydrate) can be used. 0s04 can be added as a
solid or in solution.
The osmium catalyst used in the method of the
present invention can be recycled, for re-use in sub-
sequent reactions. This makes it possible not only to
reduce the expense of the procedure, but also to recover
the toxic osmium catalyst. For example, the osmium
catalyst can be recycled as follows: Using reduction
catalysts (e.g., Pd-C), the osmium VIII species is
reduced and adsorbed onto the reduction catalyst. The
resulting solid is filtered and resuspended. NMO (or an
oxidant), the alkaloid and the substrate (olefin) are
added, with the result that the osmium which is bound to
the Pd/C solid is reoxidized to Os04 and re-enters
solution and plays its usual catalytic role in formation
of the desired diol. This procedure (represented below)
can be carried out through several cycles, thus re-using
the osmium species. The palladium or carbon can be
immobilized, for example, in a fixed bed or in a car-
tridge.
WO 92/20677 PCT/US92/03940
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H2/Pd-C
OsVIII
in solution , reduced osmium
species hound to
the~Pd/C catalyst
oxidant/aikaloid
HO
WO 92/20677 ~ ~ ~ t~ ~ ~ ~ PCT/US92/03940
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In one embodiment an olefin, such as recrystallised
traps-stilbene (C6HSCH:CHC6H5), is combined with a chiral
ligand (e. g., p-chlorobenzoyl hydroquinidine), acetone,
water and NMO. The components can be added sequentially
OS or simultaneously and the order in Which they are com-
bined can vary. In this embodiment, after the components
are combined, the resulting combination is cooled (e. g.,
to approximately 0°C in the case of traps-stilbene);
cooling can be carried out using an ice-water bath. 0s04
is then added (e.g., by injection), in the form of a
solution of Os04 in an organic solvent (e.g., in
toluene). After addition of Os04, the resulting com-
bination is maintained under conditions appropriate for
the dihydroxylation reaction to proceed.
In another preferred embodiment, a chiral ligand
(e. g., dihydroquinidine 4-chlorobenzoate), NMO, acetone,
water and Os04 (as a SM toluene solution) are combined.
The components can be added sequentially or simul-
taneously and the order in which they are combined can
vary. In this embodiment, after the components are
combined, the resulting combination is cooled (e.g., to
approximately 0°C); cooling can be carried out using an
ice-water bath. It is particularly preferred that the
combination is agitated (e. g., stirred). To this well-
stirred mixture, an olefin (e.g., traps-3-hexene) is
added slowly (e.g., by injection). The optimum rate of
addition (i.e., giving maximum ee), will vary depending
on the nature of the olefinic substrate. In the case of
traps-3-hexene, the olefin was added over a period of
about 16-20 hours. After olefin addition, the mixture
can be stirred for an additional period of time at the
WO 92/20677 PGT/US92/03940
~~~rd~3
-44-
low temperature (1 hour in the case of trans-3-hexene).
The slow-addition method is preferred as it results in
better ee and faster reaction times.
In another embodiment, a compound which accelerates
05 hydrolysis of the osmate ester intermediates (e.g., a
soluble carboxylate salt, such as tetraethylammonium
acetate) is added to the reaction mixture. The compound
(approximately 1-4 equiv.) can be added to the mixture of
chiral ligand, water, solvent, oxidant and osmium
catalyst and olefin, or prior to the addition of olefin,
if the olefin slow-addition method is used.
The diol-producing mechanistic scheme which is
thought to operate when the slow-addition of olefin
method is used is represented in Figure 4. According to
the proposed mechanism, at least two diol-producing
cycles exist. As shown in Figure 4, only the first cycle
appears to result in high ee. The key intermediate is
the osmium (VIII) trioxoglycolate complex, shown as
formula 3 in Figure 4, which has the following general
formula:
Q R,
~~~...0 ~ Rs
L ~ R ~l
wherein L is a chiral ligand and Wherein R1, R2, R3 and
R4 are organic functional groups corresponding to the
olefin. For example, Rl, R2, R3 and R4 could be alkyl,
PCT/US92/03940
WO 92/20677
-45-
aryl, alkoxy aryloxy or other organic functional groups
compatible with the reaction process. Examples of
olefins which can be used, and their functional groups,
are shown on Table 4 hereinabove.
05 This complex occupies the pivotal position at the
junction between the two cycles, and determines how diol
production is divided between the cycles.
Evidence in favor of the intermediacy of the osmium
(VIII) trioxoglycolate complex (formula 3, Figure 4) is
provided by the finding that the events in Figure 4 can
be replicated by performing the process in a stepwise
manner under stoichiometric conditions. These experi-
ments were performed under anhydrous conditions in
toluene. In the process shown in Figure 4, one equiva-
lent of the alkaloid osmium complex (shown as formula 1,
Figure 4) is allowed to react with an olefin to give the
emerald green monoglycolate ester (formula 2, Figure 4).
A different olefin is then added, followed by an equiva
lent of an anhydrous amine N-oxide, and rapid formation
of the bisglycolate ester (formula 4, Figure 4) is
observed. Upon reductive hydrolysis of the bisglycolate
ester, precisely one equivalent of each diol is liberat-
ed. These experiments indicate that a second cycle,
presumably via the osmium trioxoglycolate complex, is as
efficient as the first in producing diols from olefins.
One can also use the same olefin in both steps to run
this tandem addition sequence. When this was done using
1-phenylcyclohexene as the olefin, the ee for the first
step was 818 and the ee for the second step was 7$ in the
opposite direction (i.e., in favor of the minor
enantiomer in the first step). Thus, for this substrate
WO 92/20677 PGT~US92103940
2Q~7(~~~ _
any intrusion of the second cycle is particularly damag-
ing, and under the original catalytic conditions 1-
phenylcyclohexene only gave 8% ee (entry 3, Table 5).
Reduced ee is just part of the counterproductivity
of turning on the second cycle; reduced turnover is the
05 other liability. The bisosmate esters (formula 4, Figure
4) are usually slow to reoxidize and hydrolyze, and
therefore tend to tie up the catalyst. For example,
1-phenylcyclohexene took 7 days to reach completion under
the original conditions (the 8% ee cited above). With
slow addition of the olefin, the oxidation was complete
in one day and gave the diol in 95% yield and 78% ee
(entry 3, Table 5). '
The most important prediction arising from the
mechanistic scheme shown in Figure 4 is the minimization
of the second cycle if the olefin is added slowly. Slow
addition of the olefin presumably gives the osmium (VIII)
trioxoglycolate intermediate sufficient time to hydrolyze
so that the osmium catalyst does not get trapped into the
second cycle by reacting with olefin. To reiterate, the
second cycle not only ruins the ee but also impedes
turnover, since some of the complexes involved are slow
to reoxidize and/or hydrolyze. The optimum feed rate
depends on the olefin; it can be determined empirically,
as described herein.
The maximum ee obtainable in the catalytic process
is determined by the addition of the alkaloid osmium
complex (formula l, Figure 4) to the olefin (i.e., the
first column in Table 5). Thus, stoichiometric additions
can be used to enable one to determine the ee-ceiling
which can be reached or approached in the catalytic
WO 92!20677 ~ s~ ~~. ~ ~i ~ ~ PCT/US92/03940
-47-
process if the hydrolysis_of 3 (Figure 4) can be made to
dominate the alternative reaction with a second molecule
of olefin to give 4 (Figure 4). In the case of terminal
olefins, styrene (Table 5), the trioxoglycolate esters
05 hydrolyze rapidly, since slow addition, or the effect of
the osmate ester hydrolytic additive give only a slight
increase in the ee. However, most olefins benefit
greatly from any modification which speeds hydrolysis of
the osmate ester intermediate (3, Figure 4) (entries 2-5,
Table 5), and in extreme cases neither the effect of the
osmate ester-hydrolytic additive nor slow addition is
sufficient alone. Diisopropyl ethylene (entry 4, Table
5) approaches its ceiling-ee only when both effects are
used in concert, with slow addition carried out in the
presence of acetate. The other entries in the Table
reach their optimum ee's through slow addition alone, but
even in these cases the addition times can be sub-
stantially shortened if a compound, such as a tetraalkyl
ammonium acetate, is present.
In many cases, temperature also affects the ee.
When the ee is reduced by the second cycle, raising the
temperature can often increase it. This occurs, in
particular, when NMO is used as the secondary oxidant.
For example, d~iisopropyl ethylene gave 46$ ee at 0°C and
598 ee at 25°C (24h slow addition time in both cases).
The rate of hydrolysis of the osmium trioxoglycolate
intermediate is apparently more temperature dependent
than the rate of its reaction with olefin. This
temperature effect is easily rationalized by the expected
need to dissociate. the chiral ligand from the osmium
complex (3) in order to ligate water and initiate
WO 92!20677 PCTlUS92l03940
-48-
hydrolysis, but the ligand need not dissociate for
addition of olefin to occur (in fact this second cycle
olefin addition step is also likely to be
ligand-accelerated).
05 When K3Fe(CN)6 is used as the secondary oxidant, the
effect of temperature on the ee is opposite the effect
when NMO is the secondary oxidant. That is, lowering the
temperature can often increase the ee when potassium
ferricyanide is the secondary oxidant. Also, the olefin
need not be slowly added to the mixture but can, instead,
be added all at once when potassium ferricyanide is the
secondary oxidant. These effects and conditions
apparently occur because the second cycle is suppressed
when this secondary oxidant is used. The reactions of
the second cycle do not appreciably contribute to the
formation of diols when the secondary oxidant is
potassium ferricyanide.
The following is a description of how optimum
conditions for a particular olefin can be determined. To
optimize the osmium-catalyzed asymmetric dihydroxylation:
1) If from the known examples there is doubt about what
the ceiling-ee is likely to be, it can be determined by
performing the stoichiometric osmylation in acetone/water
at 0°C using one equivalent of the Os04 - alkaloid
complex; 2) Slow addition at 0°C: the last column in
Table 3 can be used as a guide for choosing the addition
time, bearing in mind that at a given temperature each
olefin has its own "fastest" addition rate, beyond Which
the ee suffers as the second cycle turns on. When the
olefin addition rate is slow enough, the reaction mixture
remains yellow-orange (color of 1, Figure 4); when the
WO 92/20677 PCT/US92/03940
-49-
rate is too fast, the solution takes on a blackish tint,
indicating that the dark-brown-to-black bisglycolate
complex (4, Figure 4) is being generated; 3) If the
ceiling ee is not reached after steps 1 and 2, slow
05 addition plus tetraalkyl ammonium acetate (or other
compound which assists hydrolysis of the osmate ester
intermediate) at 0°C can be used; 4) slow addition plus a
soluble carboxylate salt, such as tetraalkyl ammonium
acetate at room temperature can also be used. For all
these variations, it is preferable that the mixtures is
agitated (e. g., stirred) for the entire reaction period.
The method of the present invention can be carried
out over a wide temperature range and the limits of that
range will be determined, for example, by the limit of
the organic solvent used. The method can be carried out,
for example, in a temperature range from about 40°C to
about -30°C. Concentrations of individual reactants
(e.g., chiral ligand, oxidant, etc.) can be varied as the
temperature at which the method of the present invention
is carried out. The saturation point (e. g., the concen-
tration of chiral ligand at which results are maximized)
is temperature-dependant. As explained previously, for
example, it is possible to reduce the amount of alkaloid
used when the method is carried out at lower
temperatures.
The organic solvent used in the present method can
be, for example, acetone, acetonitrile, THF, DME,
cyclohexane, hexane, pinacolone, tert-butanol, toluene or
a mixture of two or more organic solvents. These
3fl solvents are particularly suitable when NMO is the
secondary oxidant.
WO 92!20677 PCTlUS92l03940
-50-
When potassium ferricyanide (K3Fe(CN6) is the
secondary oxidant, it is advantageous to use a
combination of solvents that separate into organic and
aqueous phases. Although the method of the present
invention can be carried out with potassium ferricyanide
05 as the secondary oxidant using the organic solvents of
the preceding paragraph, asymmetric dihydroxylation does
occur but the ee's are less than when separable organic
and aqueous solvent phases are employed.
The yields and ee's for a variety of organic
solvents, mixed with water and a variety of substrates
are shown in Tables 11-12. Table 11 shows yields and
ee's for several organic solvents (with water) for a
specific substrate. The ligand is either
DHQD-p-chlorobenzoate (PCB) or DHQD-napthyl ether. Table
12 shows the ee's for a veriety of substrates for either
t-butanol or cyclohexane as the organic phase. It is
apparent from these Tables that preferred organic phase
solvents include cyclohexane, hexane, ethyl ether and
t-butyl methyl ether. The preferred aqueous solvent is
water.
WO 92/20677 PCT/US92/03940
~~~~.,.~~ J
-sl-
Table 11. Solvent Study of Catalytic ADH using
K3Fe(CN)6
a) Solvent Effects on Styrene Diol using
DHQD-PCB Ligand
05 Reaction Time - 4 hours
off
off
Solvent Yieid('o) ee(9o)
cYciohcn~ s3.s so
Hexane 59.9 76
Iso-octane ? 76
t-BuOH 84.7 74
t-Bu-O-Me 80 73
Toluene 78 69
EtZO s8.7 68
E~OAc 64.4 6s
TIIF 61.6 61
Ct~lorobenzene 73.6 60
C113CN 79.0 s0
CH~CIZ 73.8 49
DbIF 24.s 23
McOH 84.1 3.s
WO 92120677 PfT/US92/03940
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b) Solvent Effects on Hexene Diol using
DHQD-PCB Ligand
Reaction Time - 24 hours
off
/ w
off
05 Solvent Yield(9o) ee(9o)
Cyclol~e~nne ~ 47 74 , ;
Hexane' 67.4 74
t-H uOH 84.5 74
t-8 u-O-Me 61.4 7 t
to EtIO 51.1 7I
EtOAc 26.7 71
Toluene 32.4 69
CH3CN 81.6 68
CHZCIZ 7.6 67
~5 Chlorobenzene 9.3 66
THF . 74.1 65
c) Solvent Effects on Decene Diol using
DHQD-PCB Ligand
Reaction Time ~ 24 hours
off
..
20 OEl
Solvent Yield(.o) tt(,~o)
t-BuOH 60.8 79
Cyclohetane 3.t 74
t-Hu-O-Me 7.6 71
Pf.:T/US92/03940
WO 92/20677
-53-
d) Solvent Effects on Rexene Diol using
DHQD Napthyl Ether Ligand
Reaction Time - 24 hours
off
~.-,
H
o5 Solvent Yicld(9o) ee(9'o)
t-HuOH 49.6 92 .
C clohe~ane 36.2 91
t-~ u-O-Me 75.4 89
EtZO 47.6 89
to EtOAc 41.2 88
Toluene 24.6 87
Chlocobenzene 25.0 85
T11F 78.6 83 ,
Cll3CN 90.2 81
15 CH2C1Z trace ?
e) Solvent Effects on Decene Diol using
DHQD Napthyl Ether Ligand
Reaction Time - 24 hours
N
off
~'ie~d(°/r) a
20 ~B~oH 40.7 94
5m1 of t-Bu-0-Me were added to dissolve all the ligand
*a' 6m1 of t-Bu-0-Me were added to dissolve all the liga~d
WO 92/20677 PCT1US92103940
~~~ ~~~
-54-
Table 12. Ee's of Various Substrates in the Catalytic
ADH
OH
DIiQD-PCB , cat. 0s0, , c.~.
R'
K~Ft(CM~ , K,CO, . Solrent ! N,0
H
Substrate t- BuOH Cydahtxane
73 8Q
05
I 99 99
91 92
i
~Ac 91 91
,Mt g1 93
i
eu~'eu ~9 74
74 74
In another embodiment of the present invention,
styrene was combined with a chiral ligand (DHQD),
acetone, water and NMO and Os04. The plot of amine
concentration vs second-order-rate-constant K for the
WO 92/20677 PCT/US92/03940
~.3 '"
~~~~ t~ ~;~,~
-55-
catalytic cis-dihydroxylation of styrene is represented
in Figure 2. The kinetic data of Figure 2 clearly shows
the dramatic effect of ligand-accelerated catalysis
achieved by use of the method of the present invention.
05 Point a in Figure 2 represents the rate of the catalytic
process in the absence of amine ligands (t1/2 = 108
minutes). Line b shows the rates of the process in the
presence of varying amounts of quinuclidine, a ligand
which substantially retards catalysis (at greater than
O.1M quinuclidine, t1/2 is greater than 30 hours).
Because of the observed retarding effect of quinuclidine
(ligand-decelerated catalysis) the result represented by
line C was unexpected. That is, when the process occurs
in the presence of dihydroquinidine benzoate derivative 1
(see Figure 1), the alkaloid moiety strongly accelerates
the catalytic process at all concentrations (with ligand
1 = 0.4M, t1/2 = 4.5 minutes), despite the presence of
the quinuclidine moiety in its structure.
The rate of the stoichiometric reaction of styrene
with osmium tetroxide and that of the corresponding
catalytic process were compared. The comparison indi-
cates that both have identical rate constants
~Kstoic=(5.1 ~ 0.1)x102M 1 min 1 and Kcat=(4.9 ~
2 -1 -1
0.4)x10 M min J, and that they undergo the same rate
acceleration upon addition of ligand 1. Hydrolysis and
reoxidation of the reduced osmium species, steps which
accomplish catalyst turnover, are not kinetically sig-
nificant in the catalytic process with styrene. It may
be concluded that the limiting step is the same in both
processes and consists of the initial addition reaction
forming the osmate ester (2, Figure 1). A detailed
WO 92/20677 PCT/US92/03940
i
-56-
mechanistic study reveals that the observed rate
acceleration by added ligand 1 is due to formation of an
osmium tetroxide-alkaloid complex which, in the case of
styrene, is 23 times more reactive than free osmium
tetroxide. The rate reaches a maximal and constant value
05 beyond an (approximate) 0.25 M concentration of ligand 1.
The onset of this rate saturation corresponds to a
pre-equilibrium between DHQD and osmium tetroxide with a
rather weak binding constant (Keq - 18 ~ 2 M 1). In-
creasing the concentration of DHQD above 0.25 M does not
result in corresponding increases in the enantiomeric
excess of the product diol. In fact, due to the
ligand-acceleration effect, the ee of the process
approaches its maximum value much faster than the maximum
rate is reached, which means that optimum ee can be
achieved at rather low alkaloid concentrations.
At least in the case of styrene, the rate accelera-
tion in the presence of the alkaloid is accounted for by
facilitation of the initial osmylation step. The strik-
ingly opposite effects of quinuclidine and DHQD on the
catalysis can be related to the fact that although
quinuclidine also accelerates the addition of osmium
tetroxide to olefins, it binds too strongly to the
resulting osmi~um(~I) ester intermediate and inhibits
catalyst turnover by retarding the hydrolysis/reoxidation
steps of the cycle. In contrast the alkaloid appears to
achieve a balancing act which renders it near perfect for
its role as an accelerator of the dihydroxylation
catalysis. It binds strongly enough to accelerate
addition to olefins, but not so tightly that it inter-
feres (as does quinuclidine) with subsequent stages of
the catalytic cycle. Chelating tertiary amines [e. g.,
WO 92/20677 PCT/US92/03940
~a~~~~
-56.1-
2,2'-bipyridine and (-)-(R, R)-N,N,N',N'-tetramethyl-1,2-
cyclohexanediamine) at 0.2M completely inhibit the
catalysis. Pyridine at 0.2 M has the same effect.
As represented in Table 4, the method of the present
05 invention has been applied to a variety of olefins. In
each case, the face selection rule described above has
been shown to apply (with reference to the orientation of
the olefin as represented in Figure 1). That is, in the
case of the asymmetric dihydroxylation reaction in which
the dihydroquinidine derivative is the chiral ligand,
attack occurs on the re- or re, re- face) and in the case
in which the dihydroquinine derivative is the chiral
ligand, attack occurs on the si- or si,si- face. Thus,
as demonstrated by the data presented in the Table 2, the
method of the present invention is effective in bringing
about catalytic asymmetric dihydroxylation; in all cases,
the yield of the diol was 80-95~, and with the slow-
addition modification, most olefins give ee's in the rage
of 40-90~.
The present method can be used to synthesize chiral
intermediates which are important building blocks for
biologically active chiral molecules, such as drugs. In
one embodiment, the present method was used to produce an
optically pure intermediate used in synthesizing the drug
diltiazem (also known as cardizem). The reaction is
shown in the following scheme:
WO 92/20677 PCT/US92/03940
c~ -57-
OH O
AOH
v -OChh y
H
H..OrN
................
It~CO
C ~C
Diltlazem ! Cardzom
The method of the present invention is also useful
to effect asymmetric vicinal oxyamination of an olefin,
OS and may be useful for asymmetric vicinal diamination. In
the case of substitution of two nitrogen or of a nitrogen
and oxygen, an amino derivative is used as an amino
transfer agent and as an oxidant. For example, the
olefin to be modified, an organic solvent, water, a
chiral ligand, an amino derivative and an osmium-
containing compound are combined and the combination
maintained under conditions appropriate for the reaction
to occur. The amino derivative can be, for example, an
N-chlorocarbamate or chloroamine T. Asymmetric catalytic
oxyamination of recrystallized traps stilbene, according
to the method of the present invention, is represented in
Figure 2.
WO 92/20677 ~ ~ ~ ~ ~ ~ ~ PCT/US92/03940
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In another embodiment, the present method was used
to produce intermediates for the synthesis of homo-
brassinolide and 24-epibrassinolide, which are known to
exhibit the same biological activities as brassinolide.
05 These brassinosteroids show very potent plant-growth
activity at hormonal level and access to these compounds
in a large quantity can only be achieved by synthetic
means.
OH
HO HO
HO' H0~
to brassinolide homobrassinoiide 24epi-brassinolide
OH
ADH Ho
HO
In another embodiment of the present method, highly
optically active diol was produced from the asymmetric
dihydroxylation of ethyl ~:ans-2-octenoate. This diol
WO 92!20677 PCTlUS92l03940
~ _59_
has been converted to optically pure ~-lactam structure,
which are well-known for their antibiotic activities:
OH 0 N~,,~ ~,n-Pint
0 ADH
NHOCH=Ph -~-'~' ~NOCH=Pn
OEt ~H O
Example_1 Asymmetric_Dihydroxylation_of_Stilbene
05 The following were placed sequentially in a 2L
bottle (or flask): 180.28 (1.0 M) of recrystallised trans
stilbene (Aldrich 968), 62.48 (0.134 moles; 0.134 eq) of
the p-chlorobenzoate of hydroquinidine (1), 450 mL of
acetone, 86 mL of water (the solution is 0.261 M in
alkaloid 1) and 187.2 g (1.6 mol, 1.6 eq.) of solid
N-Methylmorpholine N-Oxide (NMO, Aldrich 97$). The
bottle was capped, shaken for 30 seconds, cooled to 0-4°C
using an ice-water bath. 0s04 (4.25 mL of a solution
prepared using 0.1208 Os04/mL toluene; 0.002 Mold; 0.002
eq.) was injected. The bottle was shaken and placed in a
refrigerator at ca. 4°C with occasional shaking. A dark
purple color developed and was slowly replaced by a deep
orange one; the hEterogeneous reaction mixture gradually
became homogeneous and at the end of the reaction, a
clear orange solution was obtained. The reaction can be
conveniently monitored by TLC (silica gel; CH2C12; disap-
pearance of the starting material at a defined Rf).
After 17 hours, 1008 of solid sodium metabisulfite
(Na2S205) were added, the reaction mixture was shaken (1
minute) and left at 20°C during 15 minutes. The reaction
mixture was then diluted by an equal volume of CH2C12 and
anhydrous Na2S04 added (100 g). After another 15
WO 92/20677 PCT/US92/03940
._
-60-
minutes, the solids were removed by filtration through a
pad of celite, washed three times with 250 mL portions of
CH2C12 and the solvent was evaporated under vacuum
(rotatory-evaporator, bath temperature ~ 30-35°C).
05 The crude oil was dissolved in ethyl acetate (750
mL), extracted three times with 500 ml. portions of 2.0 M
HC1, once with 2.0 M NaOH, dried over Na2S04 and con-
centrated in vacuo to leave 190 g (89$) of the crude diol
as a pale yellow solid. The enantiomeric excess of the
crude R,R-diol was determined to be 78~ by HPLC analysis
of the derived bis-acetate (Pirkle 1A column using S~
isopropanol/hexane mixture as eluant. Retention times
are: t1 - 18.9 minutes; t2 - 19.7 minutes. Recrystalli-
zation from about 1000 ml. CH2C12 gave 150 g (70~) of
pure diol (ee - 90$). A second recrystallization gave
115g of diol (55$ yield) of 99$ ee. Ee (enantiomeric
excess) is calculated from the relationship (for the R
enantiomer, for example): percent
e.e.-[(R)-(S)/[(R)+(S)]x100.
The aqueous layer was cooled to 0°C and treated with
2. OM NaOH (about 500 mL) until pH ~ 7. Methylene
chloride was added (500 mL) and the pH adjusted to 10-11
using more 2. OM NaOH (about S00 mL). The aqueous layer
was separated, extracted twice with methylene chloride
(2x300 mL) and the combined organic layers were dried
over Na2S04. The solvent was removed in vacuo to provide
the alkaloid as a yellow foam. The crude alkaloid was
dissolved in ether (1000 mL), cooled to 0°C (ice-bath)
and treated with cry HC1 until acidic pH (about 1-2).
3D The faint yellow precipitate of p-chlorobenzoylhydro-
quinidine hydrochloride was collected by filtration and
dried under high vacuum (O.Olmm Hg).
WO 92/20677 PCT/US92/03940
-61-
The free base was liberated by suspending the salt
in ethyl acetate (500 mL), cooling to 0°C and adding 28$
NH40H until pH = 11 was reached. After separation, the
aqueous layer was extracted twice with ethyl acetate, the
05 combined organic layers were dried over Na2S04 and the
solvent removed in vacuo to give the free base as a white
foam.
Example~2 Asymmetric_pihydroxylation-of_Stilbene
To a 3 L, 3-necked, round-bottomed flask equipped
with a mechanical stirrer and two glass stoppers at room
temperature were added E-1,2-diphenylethene
(Traps-stilbene) (180.25 g, 1.0 mol, 1.0 eq),
4-methylmorpholine N-oxide (260 mL of a 60$ by wt.
aqueous solution (1.5 mol, 1.5 eq) dihydroquinidine
4-chlorobenzoate (23.25 g, 0.05 mol, 0.05 eq) 375 mL
acetone and 7.5 mL H20. The solution was 0.1 M in
alkaloid M in olefin, and the solvent was 25~ water/75$
acetone (v/v). The flask was immersed in a 0°C cooling
bath and stirred for 1 h. Osmium tetroxide (1.0 g, 4.0
mmol., 4.0 x 10 3 eq) was added in one portion producing
a milky brown-yellow suspension. The reaction mixture
was then stirred at 0°C for 24 h and monitored by silica
TLC (3:1 CH2C12:Et20 v/v). At this point, sodium
metabisulfite (285 g, 1.5 mol) was added, the mixture was
diluted with 500 mL of CH2C12, warmed to room
temperature, and stirred at room temperature for 1 h.
Anhydrous sodium sulfate (50 g) was added and the mixture
was stirred at room temperature overnight. The
suspension was filtered through a 20 cm Buchner funnel,
WO 92120677 ,~ ~, v PG'T/US92/03940
-62-
the filtrand wus :insed thoroughly w_th acetone (3 x 250
mL), and the filtrate was concentrate-d to a brown paste
on a rotary evapoz;ator with slight heating (bath
temperature 30-40°t:). The paste was dissolved in 3.5 L
05 of EtOAc, transferred to a 6 L separatory funnel, and
washed sequentially with H20 (2 x 500 mL), and brine (1 x
500 mL). The initial aqueous washes were kept separate
from the subsequent acid washes which were retained for
alkaloid recovery. The organic layer was dried (Na2S04),
and concentrated r~ give the crude diol in quantitative
yield (222.7 g, 1.')4.mol, 104%). The ee of the crude
product was deternined by 1H NMR ana'~_ysis of the derived
bis-Piosher ester ~ r, be 90%. One rec-vystallization from
hot 95% acueous a;hanol (3 mL/g) afforded 172-180 g
(80-84%) of enantinmerically pure stilbene diol as a
white solid, mp 1~: ~.5-146.5°C,
[aJD -91.1° (c~l.'?G9, abs EtOH).
Exam 1e 3 As mmetric. Dih drox lation of Stilbene
____p____ __Y___________Y____Y__________________
Asymmatric dihydroxylation of stilbene was carried
20 out as described in E::ample 1, except that 1.2 equiva-
lents of NM0 were ised.
Exam ale 4 As mmet_ic Dih drowlatio~ of Stilbe:ne
____L____ __Y____._.______2____~.______ ____________
Asymmetric dihydrotvlation of stilber_e was carried
ou;. as desc:ibed ~r~ Eample 1, except that 1 .2
25 equivalents of NMO, as a 62% wt. solLtion in ;aatEr, were
uszd.
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Example_5 Preparation-of-dihydroguinidine_derivative
Preparation of dihydroquinidine by catalytic
reduction of uinidine
_____________g______________________________
To a solution of 16.2 g of quinidine (0.05mo1) in
05 150mL of 10$ H2S04 (15 g conc H2S04 in 150mL H20) was
added 0.2 g of PdCl2 (0.022eq; O.OOllmol). The reaction
mixture was hydrogenated in a Parr shaker at 50 psi
pressure. After 2h, the catalyst was removed by filtra-
tion through a pad of celite and washed with 150mL of
water. The faint yellow solution so obtained was slowly.
added to a stirred aqueous NaOH solution (15 g of NaOH in
150mL H20. A white precipitate immediately formed and
the pH of the solution was brought to 10-11 by addition
of excess aqueous 15$ NaOH. The precipitate was col-
lected by filtration, pressed dry and suspended in
ethanol (175mL). The boiling solution was quickly
filtered and upon cooling to room temperature, white
needles crystallized out. The crystals were collected
and dried under vacuum (90°C; 0.05 mm Hg) overnight.
This gave 8.6 g (52.7$) of pure dihydroquinidine
mp~169.5-170°C. The mother liquor was placed in a
freezer at -15°C overnight. After filtration and drying
of the crystals, another 4.2 g (21.4$) of pure material
was obtained, raising the total amount of dihydroquini-
dine to 12.8 g (74.1$).
Preparation of dihydroquinidine p-chlorobenzoate
~ligand-1Z______________________________________
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From dih dro uinidine h drochloride Aldrich
________Y___g__________Y____________S_______Z
To a cooled (0°C) suspension of 100 g
dihydroquinidine hydrochloride (0.275mo1) in 300mL of dry
CH2C12 was added, over 30 minutes with efficient
05 stirring, 115mL of Et3N (0.826eq; 3eqs) dissolved in 50mL
of CH2C12. The dropping funnel was rinsed with an
additional 20mL of CH2C12. After stirring 30 minutes at
0°C, 42mL of p-chlorobenzoyl chloride (0.33mo1;57.8g;
l.2eq) dissolved in 120mL of CH2C12 was added dropwise
over a period of 2h. The heterogeneous reaction mixture
was then stirred 30 minutes at 0°C and 1 hour at room
temperature; 700mL of a 3. OM NaOH solution was then
slowly added until pH=10-11 was obtained. After part-
itioning, the aqueous layer was extracted with three
100mL portions of CH2C12. The combined organic layers
were dried over Na2S04 and the solvent removed in vacuo
(rotatory evaporator). The crude oil was dissolved in 1L
of ether, cooled to 0°C and treated with HC1 gas until
the ether solution gives a pH of about 2 using wet pH
paper. The slightly yellow precipitate was collected and
dried under vacuum to give 126 g (91.5%) of dihydro-
quinidine p-chlorobenzoate hydrochloride.
The salt was suspended in 500mL of ethyl acetate,
cooled to 0°C and treated with 28% NH40H until pH=11 was
reached. After separation, the aqueous layer was
extracted with two 200mL portions of ethyl acetate. The
combined organic layers were dried over Na2S04 and the
solvent removed under vacuum, leaving the free base 1 as
a white foam (1128; 88% overall). This material can be
used without further purification, or it can be
recrystallized from a minimum volume of hot acetonitrile
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to give an approximately 70-80$ recovery of colorless
crystals: mp: 102-104°C, [ J25D-76.5°[cl.ll, EtOH); IR
(CH2C12) 2940, 2860, 1720, 1620, 1595, 1520, 1115, 1105,
1095, 1020 cm 1; 1H NMR (CDC13) 8.72 (d, 1H, JeSHz),
05 8.05 (br d, 3H, J~9,7Hz), 7.4 (m, 5H), 6.72 (d, 1H,
3-7.2Hz), 3.97 (s, 3H), 3.42 (dd, 1H, J-9, 19.5Hz),
2.9-2.7 (m, 4H), 1.87 (m, 1H), 1.75 (br s, 1H), 1.6-1.45
(m, 6H), 0.92 (t, 3H, J-7Hz). Anal. Galcd for
C27H29C1N203: C, 69.74; H, 6.28; C1, 7.62; N, 6.02.
Found: C, 69.95;H, 6.23; C1, 7.81; N, 5.95.
_F_ro_m__d_ih_ydroguinidine
ToJa OoC solution of 1.228 dihydroquinidine
(0.0037mo1) in 30mL of CH2C12 was added 0.78mL of Et3N
(0.0056mo1; l.5eq), followed by 0.71mL of p-chlorobenzoyl
chloride (0.005mo1; l.2eq) in 1mL CH2C12. After stirring
30 minutes at 0°C and 1 hour at room temperature, the
reaction was quenched by the addition of 10~ Na2C03
(20mL). After separation, the aqueous layer was ex-
tracted with three lOmL portions of CH2C12. The combined
organic layers were dried over Na2S04 and the solvent
removed under vacuum. The crude product was purified as
described above. Dihydroquinidine p-chlorobenzoate (1)
was obtained in 91~ yield (1.5g) as a white foam.
Recovery_of-dihydroguinidine_p_chlorobenzoate
The aqueous acidic extracts (see EXAMPLE 1) were
combined, cooled to OoC and treated with 2. OM NaOH
solution (500mL) until pH=7 was obtained. Methylene
chloride was added (500mL) and the pH was adjusted to
10-11 using more 2.0M NaOH. The aqueous layer was
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separated and extracted with two 300mL portions of
CH2C12. The combined organic layers were dried over
Na2S04 and concentrated to leave the crude alkaloid as a
yellow foam. The crude dihydroquinidine p-chlorobenzoate
05 (1) was dissolved in 1L of ether, cooled to 0°C and HC1
gas was bubbled into the solution until a pH of 1-2 was
obtained using wet pH paper. The pale yellow precipitate -
of 1 as the hydrochloride salt was collected by fil-
tration and dried under high vacuum (O.Olmm Hg). The
free base was liberated by suspending the salt in 500mL
of ethyl acetate, cooling the heterogeneous mixture to
0°C and adding 28$ NH40H (or 15$ NaOH) until pH-11 was
obtained. After separation, the aqueous layer was
extracted with two 100mL portions of ethyl acetate, the
combined organic layers were dried over Na2S04 and the
solvent removed in vacuo to give 56g (91$ recovery) of
pure dihydroquinidine p-chlorobenzoate (1) as a white
foam.
Example-6 Preparation-of_dihydroguinine-derivative
Preparation_of_dihydroguinine_p-chlorobenzoate
The catalytic hydrogenation and p-chlorobenzoylation
were conducted as described for the dihydroquinidine
p-chlorobenzoate to give a white amorphous solid in
85-90$ yield. This solid can be used without further
purification, or it can be recrystallized from a minimum
volume of hot acetonitrile to afford colorless crystals:
Mp:130-133°C, (a]25D+150° (c 1.0, EtOH). The physical
properties of the solid before recrystallization (i.e.,
the "white amorphous solid") are as follows: ( ]25
WO 92/20677 PCT/US92/03940
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D+142.1 (C-1, EtOH); IR (CH2C12) 2940, 2860, 1720, 1620,
1595, 1508, 1115, 1105, 1095, 1020 cm l, 1H NMR (CDC13) d
8.72 (d, 1H, J-SHz), 8.05 (br d, 3H, J-8Hz), 7.4 (m, 5H),
6.7 (d, 1H, J-8Hz), 4.0 (s, 3H), 3.48 (dd, 1H, J~8.5,
05 15.8Hz), 3.19 (m, 1H), 3.08 (dd, 1H, J-11, lSHz), 2.69
(ddd, 1H, J-5, 12, 15.8Hz), 2.4 (dt, 1H, J-2.4, 15.8Hz),
1.85-1.3 (m, 8H), 0.87 (t, 3H, J~Hz). Anal. Calcd for
C27H29C1N203: C, f.9.74; H, 6.28; C1, 7.62; N, 6.02.
Found: C, 69.85; H, 6.42; C1, 7.82; N, 5.98.
Recovery_of-dihydroguinine_p=chlorobenzoate_(2~
The procedure is identical to treat described above
for recovery of 1.
Example-7 Procedure-for_Asymmetric_Dihydroxylation_of
Trans-3-hexene Under "Slow Addition"
Conditions
To a well stirred mixture of 0.465g (1 mmol, 0.25
eq=0.25M in L) dihydroquinidine 4-chlorobenzoate
(Aldrich, 98$), 0.7g (6 mmol, 1.5 eq) N-methylmorpholine
N-oxide (Aldrich, 97~), and 32 L of a 0.5M toluene
solution of osmium tetroxide (16 mol, 4 x 10 3 equiv),
in 4 mL of an .acetone-water mixture (10:1 v/v) at 0°C,
neat 0.5 mL (0.34g, 4 mmol) trans-3-hexene (Wiley, 99.9$)
was added slowly, via a gas tight syringe controlled by a
syringe pump and with the tip of the syringe needle
immersed in the reaction mixture, over a period of 16 h.
The mixture gradually changed from heterogeneous to
homogeneous. After the addition was complete, the
resulting clear orange solution was stirred at 0°C for an
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additional hour. Solid sodium metabisulfite (Na2S205,
1.2g) was added and the mixture was stirred for 5 min,
and then diluted with dichloromethane (8mL) and dried
(Na2S04). The solids were removed by filtration, and
05 washed three times with dichloromethane. The combined
filtrates were concentrated, and the residual oil was
subjected to flash column chromatography on silica gel
(25g, elution with diethyl ether-dichloromethane, 2:3
v/v, Rf 0.33) and collection of the appropriate fractions
afforded 0.30-0.328 (85-92% yield) of the hexanediol.
The enantiomeric excess of the diol was determined by GLC
analysis (5% phenyl-methylsilicone, 0.25 m film, 0317 mm
diameter, 29 m long) of the derived bis-Mosher ester to
be 70%.
When the above reaction Was repeated with 1.2 mL
(6mmol, l.5eq) 60% aqueous NMO (Aldrich) in 4 mL acetone,
an ee of 71% was obtained. Thus, this aqueous NMO gives
equivalent results and is almost twenty times less
expensive than the 97% solid grade. With an alkaloid
2p concentration of only O.1M (i.e., 0.186g) and with an
olefin addition period of 20 hours at 0°C, the ee was
65%. A small sacrifice in ee thus leads to a large
saving in alkaloid. At 0°C, both traps-3-hexene and
traps- -methylstyrene reach their maximum ee value
between 0.20 and 0.25M alkaloid concentration.
Exam 1e 8 As mmetric Dih drox lation of
p____ __Y___________Y____Y_________
1-Phen lc clohexene with Et~NOAc=4H~0
______Y__Y_________________ ____ _
The procedure set out in Example 1 was followed,
except that 1-phenylcyclohexene (1. OM) was substituted
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for traps-stilbene. The reaction was allowed to proceed
for three days, after which only 408 conversion to the
diol was obtained (8$ ee).
The above procedure was repeated, with the
05 difference that 2 equivalents of tetraethyl ammonium
acetate (Et4N0Ac-4H20) was added to the reaction mixture
at the beginning of the reaction. Fifty-two (52~)
percent ee was obtained using this procedure, and the
reaction was finished in about one day.
Example-9 Asymmetric_Dihydroxylation-of_trans=Stilbene
under_"phase-transfer_'_conditions_in_toluene
To a well-stirred mixture of 58.2 mg (0.125 mmol;
0.25 eq.) of the p-chlorobenzoate of hydroquinidine, 1 mL
of toluene, 88 mg (0.75 mmol; 1.5 eq.) of N-methyl-
morpholine N-oxide, 181 mg (1 mmol; 2 eq.) of tetra-
methylammonium hydroxide pentahydrate, 57 ~L (2 mmol; 2
eq.) of acetic acid, 0.1 mL of water, and Os04 (4.2 ~cL of
solution prepared using 121 mg Os04/mL toluene; 0.004
Mol$, 0.004 eq.) at room temperature, a toluene solution
(1 mL) of 90 mg (0.4 mmol) of traps-stilbene was added
slowly, with a gas-tight syringe controlled by a syringe
pump and with the tip of the syringe needle immersed in
the reaction mixture, over a period of 24 h. After the
addition was completed, 10$ NaHS03 solution (2.5 mL) was
added to the mixture, and the resulting mixture was
stirred for 1 h. Organic materials were extracted with
ethyl acetate, and the combined extracts were washed with
brine and dried o~~er Na2S04. The solvent was evaporated
under reduced pressure, and the residual oil was sub-
jected to column chromatography on silica gel (5 g,
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elution with hexane-ethyl acetate, 2:1 v/v, Rf0.17) to
afford 67.3 mg (63$) of the diol. The enantiomeric
excess of the diol was determined by HPLC analysis of the
derived bis-acetate (Pirkle 1A column using S$
05 isopropanol/hexane mixture as eluant. Retention times
are: t1 = 22.6 minutes; t2 = 23.4 minutes) to be 948.
Example_10 Asymmetric_Dihydroxylation_of_trans_Methyl
4=methoxycinnamate_under_phase=transfer
conditions in toluene
To a well-stirred mixture of 116.3 mg (0.25 eq.) of
the p-chlorobenzoate of hydroquinidine, 2 mL of toluene,
175.8 mg (1.5 mmol; 1.5 eq.) of N-methylmorpholine
N-oxide, 522 mg (2 mmol; 2 eq.) of tetraethylammonium
acetate tetrahydrate, 0.2 mL of water, and Os04 (8.4 ~L
of solution prepared using 121 mg Os04/mL toluene; 0.004
Mol~, 0.004 eq.) at room temperature, a toluene solution
(1 mL) of 192 mg (1 mmol) of trans-methyl 4-
methoxycinnamate was added slowly, with a gas-tight
syringe controlled by a syringe pump and with the tip of
the syringe needle immersed in the reaction mixture, over
a period of 24 h. After the addition was complete, 10~
NaHS03 solution (5 mL) was added to the mixture, and the
resulting mixture was stirred for 1 h. Organic materials
were extracted with ethyl acetate, and the combined
extracts were washed with brine and dried over Na2S04.
The solvent was evaporated under reduced pressure, and
the residual oil was subjected to column chromatography
on silica gel (10 g, elution with hexane-ethyl acetate,
2:1 v/v Rf 0.09) to afford 118.8 mg (53$) of the diol.
The enantiomeric excess of the diol was determined by
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HPLC analysis of the derived bis-acetate (Pickle Covalent
Phenyl Glycine column using 10$ isopropanol/hexane
mixture as eluant. Retention times are: t1 = 25.9
minutes; t2 = 26.7 minutes) to be 84$.
OS Example_11 AsYmmetric_Dihydroxylation-of-trans_Stilbene
in_the-presence_of_Boric_Acid
To a well-stirred mixture of 58.2 mg (0.125 mmol;
0.25 eq) of the p-chlorobenzoate of hydroquinidine, 70 mg
(0.6 mmol; 1.2 eq.) of N-methylmorpholine N-oxide, 37 mg
(0.6 mmol; 1.2 eq.) of boric acid, 0.5 mL of dichloro-
methane, and Os04 (4.2 ~L of a solution prepared using
121 mg Os04/mL toluene; 0.004 Mol~, 0.004 eq.) at room
temperature, a dichloromethane solution (1 mL) of 90 mg
(0.5 mmol) of traps-stilbene was added slowly, with a
gas-tight syringe controlled by a syringe pump and with
the tip of the syringe needle immersed in the reaction
mixture, over a period of 24 h. After the addition was
complete, 10~ NaHS03 solution (2.5 mL) was added to the
mixture, and the resulting mixture was stirred for 1 h.
Organic materials were extracted with ethyl acetate, and
the combined extracts were washed with brine and dried
over Na2S04. The solvent was evaporated under reduced
pressure, and the residual oil was subjected to column
chromatography on silica gel (5 g, elution with hexane-
ethyl acetate, 2:1 v/v, Rf 0.17) to afford 78.3 mg (73$)
of the diol. The enantiomeric excess of the diol was
determined by 1H-NMR (solvent: CDC13) analysis of the
derived bis-Mosher ester to be 94~.
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Example_12 Asymmetric_Dihydroxylation_of_trans-Methyl
4_methoxycinnamate-in_the-presence_of_Boric
Acid
To a well-stirred mixture of 116.3 mg (0.25 mmol;
05 0.25 eq.) of the p-chlorobenzoate of hydroquinidine,
175.8 mg (1.5 mmol; 1.5 eq.) of N-methylmorpholine
N-oxide, 74.4 mg (1.2 mmol; 1.2 eq.) of boric acid, 1 mL
of dichloromethanf., and Os04 (8.4 ~cL of a solution
prepared using 121 mg Os04/mL toluene, 0.004 mol$, 0.004
eq.) at room temperature, a dichloromethane solution
(1mL) of 192 mg (1 mmol) of traps-methyl 4-
methoxycinnamate Was added slowly, with a gas-tight
syringe controlled by a syringe pump and with the tip of
the syringe needle immersed in the reaction mixture, over
a period of 24 h. After the addition was complete, 10~
NaHS03 solution (5 mL) was added to the mixture, and the
resulting mixture was stirred for 1 h. Organic materials
were extracted with ethyl acetate, and the combined
extracts were washed with brine and dried over Na2S04.
The solvent was evaporated under reduced pressure, and
the residual oil was subjected to column chromatography
on silica gel (10 g, elution with hexane-ethyl acetate,
2:1 v/v, Rf 0.09) to afford 151.1 mg (67$) of the diol.
The enantiomeric excess of the diol was determined by
HPLC analysis of the derived bis-acetate (Pirkle Covalent
Phenyl Glycine column using 10$ isopropanol/hexane
mixture as eluant. Retention times are: t1 s 24.0
minutes; t2 ~ 24.7 minutes) to be 76$.
Example-13 Asymmetric-Dihydroxylation_of-traps=~_
Methylstvrene_in_the_presence_of-Boric_Acid
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To a well-stirred mixture of 58.2 mg (0.125 mmol;
0.25 eq) of the p-chlorobenzoate of hydroquinidine, 70 mg
(0.6 mmol; 1.2 eq) of N-methylmorpholine N-oxide, 72 mg
(0.6 mmol; 1.2 eq) of phenylboric acid, 0.5 mL of
05 dichloromethane, and Os04 (4.2 ~L [of a solution prepared
using 121 mg Os04/mL toluene; 0.004 Mol~, 0.004 eq) at
0°C, a dichloromethane solution] (0.5 mL), 65p,L (0.5
mmol) trans-~-methylstyrene was added slowly, with a
gas-tight syringe controlled by a syringe pump and with
the tip of the syringe needle immersed in the reaction
mixture, over a period of 24 h. After the addition was
complete, 10~ NaHS03 solution (2.5 mL) was added to the
mixture, and the resulting mixture was stirred for 1 h.
Organic materials were extracted with ethyl acetate, and
the combined extracts were washed with brine and dried
over Na2S04. The solvent was evaporated under reduced
pressure, and the residual oil was subjected to column
chromatography on silica gel (5 g, elution with hexane-
ethyl acetate, 2:1 v/v, Rf 0.62) to afford 109 mg (91~)
of the phenylborate. The phenylborate was dissolved into
acetone (3 mL) and 1,3-propandiol (0.5 mL), and the
resulting mixture was stood for 2 h at room temperature.
The solvent was evaported under reduced pressure, and the
residual oil c~as subjected to column chromatography on
silica gel (5g, elution with hexaneethyl acetate, 2:1
v/v, Rf 0.10) to afford 48.6 mg (70$) of the diol. The
enantiomeric excess of the diol was determined by HPLC
analysis of the derived bis-acetate (Pirkle 1A column
using 0.5$ isopropanol/hexane mixture as eluant.
Retention times are: t1 = 17.1 minutes; t2 = 18.1
minutes) to be 73$.
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Example_14 General-Method for_the_Asymmetric
Dihydroxylation_of_trans=Stilbene_Using_A
Pol meric Alkaloid Li and
___Y_________________8___
To a magnetically stirred suspension of the alkaloid
05 copolymer (such as polymers 2-4, Table 1; 0.25 eq based
on alkaloid incorporated), NMO (1.5 eq), and tetraethyl-
ammonium acetate tetrahydrate (1.0 eq) in acetone-water
(10/1, v/v) a solution of Os04 (0.01 eq) in either
toluene or acetonitrile was added. After stirring for
10-30 minutes, traps-stilbene (1.0 eq) was added and the
reaction mixture was stirred for the given time and
monitored by silica gel TLC (hexane-EtOAc 2/1, v/v). The
concentration of olefin in the reaction mixture was
0.3-0.4 M. After the reaction was complete, the mixture
I5 was diluted with acetone, water, hexane or ether and
centrifuged or filtered to separate the polymer from the
reaction mixture. The supernatant was then worked up as
described by Jacobsen et al., J._Am.-Chem._Soc., 110:1968
(1988).
Example_15 Asymmetric_Dihydroxylation_of_trans-Stilbene
Using_A_Polymer-Bound-Alkaloid-Ligand-and
Potassium-Ferricyanide
To a well-stirred mixture of the alkaloid polymer
(0.05 mmol, based on alkaloid incorporated), potassium
ferricyanide (0.198 g, 0.6 mmol) and potassium carbonate
(0.83 g, 0.6 mmol) in tert-butanol (1.5 mL) and water
(1.5 mL), was added Os04 solution (0.0025 mmol) in
acetonitrile. Afr.er stirring for 10 min, traps-stilbene
(36 mg, 0.2 mmol) was added and the mixture was stirred
for the given time and monitored by silica gel TLC. When
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the reaction was complete, water (3.0 mL) was added and
the mixture was filtered. The filtrate was extracted
with dichloromethane (5 mL x 2). the organic layer was
stirred for 1 h with excess sodium metabisulfite and
05 sodium sulfate. This suspension was filtered and the
filtrate was concentrated to provide crude diol, which
was purified on a silica gel column.
Example_16 AsYmmetric~Dihydroxylation_of_Olefins
in_the_Presence_of-Potassium_Ferricyanide
The general procedure for asymmetric dihydroxylation
of olefins using potassium ferricyanide:
To a well-stirred mixture of 0.465 g (1 mmol, 0.5
equiv ~ 0.033 M in ligand) dihydroquinidine
p-cholorobenzoate (Aldrich, 98~), 1.980 g (6 mmol, 3.0
equiv) potassium ferricyanide, 0.8308 (6 mmol, 3.0 equiv)
potassium carbonate, and 0.5 mL of a 0.05 M tert-butyl
alcohol solution of osmium tetroxide (0.025 mmol, 0.0125
equiv) in 30 mL of a tert-butyl alcohol-water mixture
(1:1, v/v) at room temperature, olefin (2 mmol) was added
at at once. The reaction mixture was stirred for 24 h at
room temperature. Solid sodium sulfite (Na2S03, 1.58)
was added, and the mixture was stirred for an additional
hour. The solution obtained was concentrated to dryness
under reduced pressure, and the residue was extracted
with three portions of ether. The combined extracts were
dried (Na2S04) and evaporated. The residue was purified
by column chromatography (silica gel,
dichloromethane-ether).
Example_17 Preparation-of_9_0=Phenvldih~rdroguinidine
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To a suspension of dihydroquinidine (4.0 g) in THF
(40 mL) Was added r~-BuLi (2.5 M solution in hexane, 4.95
mL) at 0°C. The ice bath was removed and the reaction
mixture stood at room temperature for 10 minutes. To the
05 resulting yellow solution, solid cuprous chloride (1.2 g)
was added. After stirring for 30 minutes, pyridine (30
mL) and HMPA (1 mL) were added. After stirring for 5
minutes, phenyl iodide (1.37 mL) was added and the
mixture was stirred at reflux for 36h. To the resulting
mixture, aqNH40H was added and the mixture was extracted
with ethyl ether. The extract was dried over MgS04. The
solvent was evaporated under reduced pressure, and the
residue was subjected to column chromatography on silica
gel (100 g, elution with ethyl acetate-ethanol, 9:1 v/v,
j5 Rf 0.23) to afford 1.77 g(y. 36$) of 9-0-phenyldihydro-
quinidine.
1H NMR (CDC13) b 8/68 (1H, d, J = 4.5 Hz), 8.08 (1H, d, J
= 9 Hz), 7.3-7.5 (3H, m), 7.17 (2H, t, J = 8 Hz), 6.89
(1H, t, J = 8 Hz), 6.78 (2H, d, J = 8 Hz), 6.02 (1H, d, J
= 3 Hz), 4.00 (3H, s), 2.7-3.3 (5H, m), 2.2-2.4 (1H, m),
1.4-1.9 (6H, m), 1.1-1.3 (1H, m), 0.97 (3H, t, J = 7 Hz).
Example-18 AsYmmFtric_Dihdroxylation_of_Trans-3-Hexene
Using_9=0-Phenyldihydroguinidine_and
Potassium_Ferr_i_cyanide
To a well-stirred mixture of 46 mg of 9-0-phenyl-
dihydroquinidine, 396 mg of potassium ferricyanide, 166
mg of potassium cabonate and 8 ~L of a 0.63 M toluene
solution of osmium tetroxide in 6 mL of t-butyl alcohol-
water (1:1, v/v) at room temperature was added 50 ~L of
trans-3-hexene all at once. The reaction mixture was
WO 92/20677 PCT/US92/03940
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stirred for 20 h at room temperature. Solid sodium
sulfite was added and the mixture was stirred for 3 h.
The solid was removed by filtration and the filtrate was
extracted with ethyl ether. The extract was dried over
05 mgS04. The solvent was evaporated under reduced pres-
sure, and the residue was subjected to column chroma-
tography on silica gel (elution with hexane-ethyl
acetate, 2:1 v/v) to afford 40.5 mg (y. 85~) of the diol.
The enantiomeric excess of the diol was determined by GLC
analysis of the derived bis-Mosher ester to be 83~ (5~
phenyl-methylsilicone, 0.25 m film, 0.317 mm diameter,
29 m long. Retention times are t1 = 15.6 min; t2 - 16.0
min.).
Example~19 Asymmetric_Oxyamination_of_Trans-Stilbene
Using_N=Chloro=N_Sodio~t=ButYlcarbamate
To a well-stirred mixture of 81 mg trans-stilbene,
122 mg of N-chloro-N-sodio-t-butylcarbamate, 95 mg of
murcuric chloride, 209 mg of dihydroquinidine p-
chlorobenzoate and 370 ~L of water acetonitrile (5 mL)
was added 9 ~L of a 0.5 M toluene solution of osmiur,
tetroxide. The mixture was stirred at room temperature
overnight. Solid sodium sulfite and water were added,
and the mixture was stirred at 60°C for 1 hour. The
mixture was extracted with dichloromethane and the
extract was dried over MgS04. The solvent was evaporated
under reduced pressure, and the residue was subjectec to
column chromatography on silica gel (elution with he~:ane-
ethyl acetate, 4:1 v/v, Rf 0.13) to afford 13i r.:g (_;_
93~) of the aminoalcohol. The enantiomeric excess o~ thr
~~~~~3~
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aminoalcohol was determined by HPLC analysis (Pickle
Covalent Phenyl Glycine column using 10% isopropanol/
hexane mixture as eluant. Retention times are: t1 -
12.7 min; t2 ~ 15.2 min.) to be 65%.
05 1H NMR (CDC13) X7.1-7.4 (10H, m), 5.3-5.4 (1H, m), 4.95
(1H, d, J - 3.5 Hz), 4.8-5.0 (1H, m), 2.6-2.7 (1H, m),
1.34 (9H, ).
Exam 1e 20 As mmetric Dih drox lation Usin Heteroc clic
____E_____ __Y___________Y____Y___________~________Y____
Chiral Li ands
g____
Li and re arations and ro erties
__g____Q__E_____________P__P______
la: To a room temperature suspension of DHQD (48.9
g, 0.15 mol) in dry DMSO (600 ml) are added NaH (4.0 g,
0.17 mmol) followed by pyridine (12.1 ml, 0.15 mol), CuI
(28.6 g, 0.15 mol), and then 9-phenanthryl iodide (45.6
g. 0.15 mol) under argon. After 70 h of reaction at
120°C, la is obtained in 73% yield (55.0 g). See also:
Lindley, J. Tetrahedron, 1984, 40, 1433 and references
therein.
m.p. 98-100°C, 1H NMR (250 MHz, CDC13): d-8.7 (m,2), 8.38
(d, l), 8.07 (d, l), 7.75 (m,2), 7.57 (d, l), 7.4 (m,6),
6.63 (s, l), 6.63 (d, l), 4.03 (s,3), 3.38 (m, l), 3.16
(m, l), 2.97 (m,2), 2.78 (m, l), 2 5S (s,br.,l), 2.39
(t,1), 1.81 (s,1), 1.6 (m,6), 0.98 (t,3). 13C NMR (75
MHz, CDCI3): d - 158.2, 150.4, 147.5, 144.6, 143.7,
132.3, 132.0, 131.5, 127.4, 127.2, 126.7, 126.6, 126.4,
124.5, 122.8, 122.2, 121.9, 118.1, 104.8, 100.9, 78.8,
60.3, 55.8, 51.0, 50.1, 37.4, 27.1, 26.6, 25.2, 21.7,
11.8. IR (KBr): v ~ 1622, 1508, 1452 and 1227 cm 1.
[a]D23 ~ -281.3 (CHCI3, c -
1.12 g ml 1).
WO 92/20677 PCT/US92/03940
~~s, >( .ri, .: ~ ,;.
X41. ~ 13 ~
-79-
1b: To a room temperature suspension of DHQD (65.2 g,
0.20 mol) in DMF (300 ml) are added NaH (6.06 g, 0.24
mol), followed by 2-chloro-4-methylquinoline (42.6 g,
0.24 mol). After stirring for 24 h at room temperature,
05 2a is obtained in 82~ yield (76.3 g).
m.p. 151-153°C. 1H NMR (250 MHz, CDCI3): d = 0.93 (3H,t,J
= 7.2Hz), 1.4-1.7 (6H,m), 1.76 (lH,s), 2.12 (lH,t,J =
lO.OHz), 2.61 (3H,s), 2.7-3.0 (4H,m), 3.43 (lH,dd,J =
6.4,8.8Hz), 3.94 (3H,s), 6.82 (lH,s), 7.2-7.6 (6H,m),
7,73 (lH,d,J ~ 2.5Hz), 7.81 (lH,d,J = 8.OHz), 7.98(lH,d,J
= 9.2Hz), 8.67 (lH,d,J = 4.6Hz). 13C NMR (CDCI3) b =
11.8, 18.4, 22.9, 25.2, 25.8, 27.1, 37.2, 49.8, 50.6,
55.4, 59.2, 73.1, 101.7, 112.5, 118.5, 121.4, 123.3,
123.7, 125.2, 127.5, 129.0, 131.3, 144.5, 145.8, 147.3,
157.4, 160.4.IR(KBr): 1608, 1573, 1508, 1466, 1228, 1182,
1039, 848, 758 cm 1. [a]D21 a -194.7° (EtOH, c = 1.0).
2a and 2b can be synthesized in a similar fashion. Like
the p-chlorobenzoate derivatives, these two new types of
ligands are now available from Aldrich.
Typical-Procedure_for_the-CatalYtic_ADH_(vinlycYlooctane)
To a well-stirred mixture of DHQD-PHN la (100mg, 0.2
mmol. 0.02 equiv,), K3Fe(CN)6(9.88 g, 30 mmol, 3 equiv.),
and K2C03 (4.15 g. 30 mmol, 3 equiv.) in a tert-BuOH-H20
mixture (100 ml, 1/1, v/v) was added potassium osmate
(VI) dihydrate (7.4 mg, 0.02 mmol, 0.002 equiv.). The
resulting yellow solution was cooled to 0°C and
vinylcyclooctane (1.65 ml, 10 mmol) was added. The
reaction mixture was stirred for 18 h at 0°C. Na2S03
(7.5 g) was added and the resulting mixture was stirred
for 30 minutes. The two phases were separated and the
PCT/US92/03940
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aqueous phase was then extracted with CH2C12. The
combined organic solution was evaporated and the residue
was diluted with ethyl acetate, washed with 1 M H2S04,
aqueous NaHC03, and brine, and dried. Concentration and
05 flash chromatography affored 1.63 g (95$) of
cyclooctylethanediol as a colorless oil; [a]D22--4.1°
(EtOH, c-1.0). The ee of the diol was determined by HPLC '
analysis of the derived bis-MTPA ester to be 93$. The
alkaloid ligand was recovered in 82~ yield by adjusting
the acidic aqueous washes to pH 11 with Na2C03,
extracting with CH2C12.
Example_21 Asmmetric_Dihydroxylation-of-Olefins_Using
9-0=phenanthryl-and_9=0_naphthyl
dihydroguinidine_Ligands
This example describes the enantioselectivity-ligand
structure relationship of the 9-0-aryl DHQD ligands which
explains the advantages of these new ligands.
The enantiometric excesses obtained in the catalytic
ADH reactions of various olefins using 9-0-aryl DHQD are
summarized in Table 13. These 9-0-aryl DHQD ligands can
be easily prepared in one step from commercially
available hydroquinidine, NaH, CuI, and the corresponding
aryl halide in moderate to good yields (52-70~), as
describe below. Compared to DHQD p-chlorobenzoate 1,
WO 92120677 PCT/US92103940
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Table 13: Catalytic Asymmetric Dihydroxylation
of Olefinsa
b
ee,
'
olefin : ' ~ ~ i , ~'~' ~""' ~"~., eu E~.', E~ ~H~ ~, co~c
a
05 10~ 99 91 91 79 74 67
~,,, " s ~ 94 89 91 88 83 88
R:3
99 91 96 94 92 94
~N
99 93 98 96 92 94
aAll reactions were carried out as described by Kwong,
H.-L., et al., _T_et_r_a_h_e_d_r_o_n__L_e_t_t_., _3_0:2041 (1989), except
that 25 mol8 of ligand was used Reactions were
performed at room temperature. bIn all cases the isolated
yield of the diol was 75-95$. The enantiomeric excesses
were measured by conversion of the diol into the
corresponding bisesters of (R)-(+)-a-methoxytrifluoro-
methylphenylacetic acid and determination of the ratio of
diasteromers by GLC, HPLC, and/or H
9-0-phenyl DHQD 2 is obviously a better ligand for
aliphatic olefins, but not for aromatic olefins. By
contrast, 9-0-naphthyl 3 and especially, 9-0-phenanthryl
DHQD 4 exhibit much higher enantioselectivities for both
aromatic and aliphatic olefins.
In order to obtain information regarding the
relationship between ligand structure and
enantioselectivity in the ADH, various 9-0-substituted
DHQD derivatives were next examined. The structures of
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the 9-0-substituents of these DHQD derivatives and their
enantioselectivities for the typical aliphatic and
aromatic olefins, traps-5-decene and traps-stilbene are
shown in Table 14. Each structure in Table 14 is drawn
05 with its expected spatial orientation in the reaction
intermediate, osmate ester such that the more sterically
hindering 6-methoxyquinoline moiety is on the left side
of the structurell.
In Group A, those derivatives having a second
benzene ring on the right side (1,3 and 4) all give
higher ee's for stilbene (99%) than the one (2) without
that second benzene ring (94%). In addition, the
naphthyl derivative (3) gives higher ee for decene (94%)
than does the phenyl derivative (2) (88%). These two
results suggest that the benzene ring on the right side
is important for high enantioselectivities with both
aliphatic and aromatic olefins. On the other hand, the
fact that derivatives (2-4) give much higher ee's for
decene (88-96%) than does the p-chlorobenzoate derivative
(1) (79%) shows the importance of the aromatic ring on
the left side for aliphatic olefins.
Next, the o-position of the phenyl derivatives was
examined (2, 5-7, Group B). While the phenyl-derivative
(2) and the 2-methylphenyl derivative (6) give fairly
high ee's for decene (88, 91%), the 2-pyridyl (5) and the
2,6-dimethylphenyl (7) derivatives do not produce
satisfactory enantioselectivities (71, SO%). This
indicates that the left o-position of the phenyl
derivative needs to be just C-H for high
enantioselectivity. The effect at m- and p-positions can
be understood by comparing the derivatives in Group C and
D. These results indicate that both the m- and
p-positions need to be C-H or larger for high ee's with
aliphatic olefins.
pGTlUS92/03940
WO 92!20677
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Table 14
R04' H
N
decene R eliibene dec ~e R s~ilbene decene R stttbene decene R. stilbene
° ~ e6 %~ (e8 %) : (e8 %) (e8 %) ~ (e8 %)
fee x) (ee Yo) (e8 )
a . .. .. .. ...
,. 2 3 ~ . _
o ~ H ~; 94 94 ~ : ~ ~ 99 93 ~;, 97
os 1 ..... . ... ... ..... 11
?9 '~ N ~
.M; S ~, ~ .
... " ..
' S ~ ' 12
... .. ....9~ 8 95 ~~ 98 8a ,",. ..-94
88 ~ 94 71 ,",, , ,",, ,
,rv~~ . . ,
3 . . .. . ~' ..
6 ' ..... 9
94 ~~ 99 1 H~~~ 95 87 ,",, ; i 96
9 '
~ : IAA N '
. . to .
.. ~ ,~,,, '~. ~. Not 92. ~,~,, ~ .. - 96
... . 50
4 g6 , 99 '"'" ; Tested
G~~p A G~up B Group C Group D
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Procedure for the S nthesis of 9-0-ar 1 DH D 3 and 4
___________________Y_________________Y____Q__S_Z_____S_Z
Into a 100 ml 3-necked round-bottomed flask 2.00g
(6.12 mmol) of dihydroquinidine (Note: All addition of
reagents and reaction were done under argon) and 0.160g
OS (6.73 mrnol) of NaH were dissolved in 20m1 of
dimethylsulfoxide. After stirring for about 10 minutes
the reaction mixture became a clear orange-yellow
solution. At this point, 1.178 (6.12 mmol) of copper(1)
iodide and 0.50 ml (6.12 mmol) of pyridine and 6.12 mmol
of 1-naphthyl iodide or phenanthryl bromide,
respectively, were added and the reaction mixture was
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heated for 3 days at 120°C. Then the reaction mixture
was allowed to cool down to room temperature and
dichloromethane (30 ml) and water (30 ml) were added.
Next, 10 ml of concentrated ammonium hydroxide was slowly
05 added to the reaction mixture. After stirring for 15
minutes the two phases were separated. The aqueous phase
was extracted two times with dichloromethane (20 ml). -
The organic phases were combined, washed three times with
water (10 ml), and evaporated. The resulting residue was
then purified by column chromatography (silica gel, using
5~ methanol/ethyl acetate as the eluting solvent),
yielding slightly yellow crystals of 9-0-naphthyl DHQD
(3) (yield: 70$) or 9-0-phenanthryl DHQD (4) (yield: 52$)
respectively.
(3): m.p. 75-77°C. 1H NMR (250 MHz, CDCI3): 6 a 8.60
(dd,2), 8.05 (dd,l), 7.80 (d, l), 7.4 (m,5), 7.07 (t, l),
6.42 (d, l), 6.24 (d, l), 3.99 (s,3), 3.31 (dt,l), 3.17
(dd,l), 2.92 (dd,2), 2.78 (m, l), 2.37 (m,2), 1.79 (s,br.,
1), 1.6 (m,6), 0.96 (t,3). 13C NMR (75 MHz, CDCI3): 6 =
158.2, 150.4, 147,5, 132.3, 132.0, 131.5, 127,4, 127.2,
126.7, 126.6, 126.4, 124.5, 122.8, 122.2, 121.9, 118.1,
104.8, 100.9, 78.8, 60.3, 55.8, 51.0, 50.1, 37.4, 27.1,
26.6, 25.2, 21.7, 11.8, IR (KBr): v s 1622, 1508, 1452
and 1227 cm 1. [a)D23 ~ -281.3 (CHCI3, c = 1.12g ml 1)
The 9-0-aryl DHQD (3) and (4) were prepared
according to the Ullmann phenyl ether synthesis: Lindley,
J., Tetrahedron, 40:1433 (1984) and references therein.
All these 9-0-substituted DHQD derivatives (5), (9)
and (10) were synthesized at room temperature without
copper(I) iodide.
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Example_22 Asymmetric_Dihydroxylation_of_Olefins_Using
Dihydroguinine-Arylethers
A high level of asymmetric induction was achieved in
the asymmetric dihydroxylation of a wide variety of
05 olefins using 9-0-aryldihydroquinines as ligands. (B.
Lohray, et al., Tetrahedron_Lett., 30:2041 (1989))
The asymmetric dihydroxylation using catalytic
amounts of osmium tetroxide and cinchona alkaloid
derivatives is one of the few examples of reactions
combining high levels of enantioselectivity for a large
range of substrates, good to excellent yields, simple and
mild experimental conditions. Another point worth
emphasizing, is the availability of the requisite
cinchona alkaloids. Both enantiometers of the diol can
be obtained choosing dihydroquinine (DHQ) or
dihydroquinidine (DHQD) derivatives):
dihydroqulnidlne derlvatlvea R.
(DHQD) ~H
1 b-4 b A~ H
"HO OH" 1% or less Os04 R3 OH
K3Fe(CtJ)6, K2C03 R2
3 1 2 R,
t- T tBuOH, Hz0 OH
-HO OH"
A
d~nydroquln~ne derlvatwea A.~_~'~_H
(oHat
1 a-4 a
ct _
\ /
7 e,b R: ~ 2a,b R: / \ 3a,b R: - 4a,b R: \
O
WO 92/20677 PCT/US92/03940
~~~~U~S
Recent advances in our group using potassium
ferricyanide as stoichiometric oxidant and new aryl and
heteroaromatic derivatives of the dihydroquinindine and
dihydroquininine have made it possible to obtain good to
05 excellent yields and enantioselectivities for many
different kinds of substrates. (H-L. Kwong, et al.,
Tetrahedron_Lett., 31:2999; M. Minato, et al., J.-Org_
Chem., 55:766 (1990); T. Shibata, et al., Tetrahedron
Lett., 31:3817 (1990); In this example we report details
about the 9-0-aryldihydroquinines 2a-4a.
The trend for the dihydroquinine and
dihydroquinidine derivatives are very similar (see Table
15). As in the dihydroquinidine series, the DHQ
phenanthryl ether derivative 4a is greatly superior to la
for a wide range of substrates. The improvement is
especially dramatic for transdisubstituted aliphatic
olefins such as 5-decene (entry 1) as well as for
terminal saturated olefins (entries 6 and 7) and for
alkyl substituted a,~ unsaturated carbonyl compounds
(entry 3). The changes observed in case of aromatic
olefins (entries 4 and 5) were slight.
WO 92/20677 PCT/US92/03940
~~'~~~~J
_88_
Table 15
1 mol°,6 OSO~ R3 OH
~R2 25 m01% 1-4 a Of b R2
f11 \ ~ R1
t-butanol I Hz0 OH
K3Fe(CN)6l K2C03
ee using Ia ee using ee using ee using
2a 3a 4a
entry olefin (ee using (ee using (ee using (ee using
1b) 2b) 3b) 4b)
I rBu ~nBy 70% ( 79% ) 75% ( 88% 86% ( 94% 9196 ( 96%
)' )
[93%j~
05 2 /~%~/ 67% ( 74% ) 75% ( 83% 82% ( 92% 85% ( 94%
) )
3 O 64% 70% 83% 9I%
~OEt [ 94%J ~
4 Ph ~~ 97% ( 93% ( 94% 946 ( 99% 96% ( 99%
99% ) ) ) )
~~ ~ 66%(74%) 57%(61%) 62%(72%) 69%(73%)
6 I-decene 41% ( 44% 56% ( 66% 63%
45% ) )
7 54% ( 58% 73% ( 84% 83%( 88%)
64% ) )
~ [88%(93%))~
All but the three indicated reactions were carried out at
room temperature. In all cases the isolated yield was
70-95$. Enantiomeric excesses were determined by GC or
HPLC analysis of the derived bis-Mosher esters.
WO 92120677 PCT/US92/03940
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Unlike the difference observed using the
dihydroquinidine derivatives, the gap in
enantioselectivities between naphthyl-DHQ and
phenanthryl-DHQ is significant (fee - 2-108 at RT versus
05 1-48 for DHQD derivatives). Especially noteworthy is the
fact that the differences of selectivities obtained using
4a and 4b is very small for all examples in Table 12 and
therefore enantiomers of the diol are available in almost
the same optical purity.
The reaction can be successfully carried out at 0°C
with a significant improvement of enantioselectivity
especially for terminal olefins (entries 1,3 and 7).
In conclusion, we want to point out that from a
large variety of olefinic substrates, it is now possible
to obtain vicinal diols in excellent yields, with good to
excellent enantiomeric enrichments for both diol
enantiomers using either dihydroquinine or
dihydroquinidine.
Example-23 Synthesis_of-Methylphenylcarbamoyl
__ ___ ________ ___ __ _dihydroguinidine_(MPC_DH(3D~:
Dihydroquinidine (1.4 g, 4.3 mmol, 1 eq) was
dissolved in 15 ml of CH2C12 under nitrogen atmosphere in
a 3-necked 100 ml round bottom flask. At room
temperature, 2 ml of triethylamine (14.4 mmol, 3.3 eq)
Was added to the solution and stirred for 30 minutes.
N-methyl-N-phenylcarbamoyl chloride (1.6 g, 9.4 mmol, 2.2
eq) was dissolved in 6 ml CH2C12 and added to the
reaction mixture aropwise via an addition funnel. The
reaction mixture was stirred under N2 for three days
before reaching reaction completion. 50 ml of 2N haOH
were added, and the phases were separated. The CH2C12
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layer was saved, and the aqueous phase was extracted with
50 ml of CH2C12. The CH2C12 phases were combined and
dried over MgS04 before being concentrated down to afford
a gummy pink material. Purification via flash
05 chromatography (silica gel, 95.5 EtOAc/Et3N, v/v)
afforded a yellow material which was then crystallized
from CH3CN to obtain white starlike crystals (1.27 g, 65$
yield).
Characterization:
mp. 119-120° C. High resolution mass spec; calculated
molecular mass-459.25217 amu, found-459.2519 amu.
1H NMR (300 MHz, CDC13 with TMS); 8.7 b (d, 1H), 8.0 d .
(d,lH), 7.2-7.4 d (m, 7H) 6.4 b (d, 1H), 3.8 d (s,3H),
3.3 S (s,3H), 3.1 6 (1H), 2.8 b (q, 1H), 2.6 d (m, 3H),
1.7 5 (s,2H), 1.3-1.4 S (m7H), 0.9 b (t, 3H).
13C NMR (75 MHz, CDC13 with TMS): 12.1 d, 23.9 b, 25.3 b,
26.2 b, 27.3 b, 37.5 S, 38.2 b, 49.8 b, 50.7 6, 55.5 b,
59.7 b, 75.6 d, 75.6 b, 101.8 b, 119.1 b, 121.8 d,
126.3 d, 126.7 S, 127.3 6, 129.1 b, 131.7 b, 143.1 b,
144.7 b, 144.9 b, 147.5 b, 152.1 b, 154.8 b, 157.7 6.
Example_24 Asymmetric_Dihydroxylation-of-Olefins
Using_9-0=Carbamoyl_DihYdroguinidine
Li ands
g____
Typical Procedure for the Catalytic ADH (cis
___-
methylstyrene):
To a well-stirred solution of DHQD-MPC (dihydroquinidine
methylphenylcarbamate) (10 mg, 0.02 mmol, 0.10 equiv),
K3Fe(CN)6 (200 mg, 0.6 mmol, 3 equiv), K2C03 (85 mg, 0.6
mmol, 3 equiv) in a tert-butanol/water solution (6 ml,
1/1, v/v), osmium tetrokide was added in acetonitrile
WO 92/20677 PCT/US92/03940
~~~~~, j~J A. -91-
solution (0.5 M, 4 ~1, 0.01 equiv) at room temperature.
After stirring for ten minutes, cis-~-methylstyrene (26
~1, 0.2 mmol) was added. The reaction mixture was
stirred at room temperature, and reaction progress was
05 monitered by thin layer chromatography. Upon reaction
completion (less than two hours), the phases were
separated. The aqueous phase was extracted with CH2C12.
The tent-butanol and CH2C12 fractions were combined and
stirred for one hour with excess sodium metabisulfite and
sodium sulfate. Concentration followed by flash
chromatography afforded the diol (24.4 mg, 82~ yield) as
an off-white solid. Enantiomeric excess (ee) of the diol
(46$ ee) was determined by GC analysis of the bis-MPTA
ester derivative.
