COMPOSES .alpha.-DIOL .gamma.-DIOXOIQUES

PROCESS FOR THE PREPARATION OF .alpha.-DIOL-.gamma.-DIOXO COMPOUNDS

Abrégé anglais

ABSTRACT OF THE DISCLOSURE

The invention relates to a process for the preparation
of-.alpha.-diol-?-dioxo compounds having the general formula:

Image

in which R1 and R4 which may be identical or different, each
represent a lower alkyl radical and R2 and R3 each represent a
hydrogen atom, comprising reacting a compound having the
general formula:
Image

wherein R1, R2, R3, R4 have the above meanings with an oxidizing
mixture consisting of osmium tetroxide and an alkaline or alkaline
earth metal chlorate, in the presence of water. The ?-diol-?
dioxo compounds according to the present invention are useful
synthesis intermediates, for instance in the preparation via
cyclization of furane derivatives, some of which may be
employed as flavorants and perfumes.

Revendications

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:



1. Process for the preparation of ?-diol-?-dioxo
compounds having the general formula:



Image

in which R1 and R4, which may be identical or different, each
represent a lower alkyl, and R2 and R3 each represent a
hydrogen atom, which process comprises reacting a compound
having the general formula:


Image

wherein R1, R2, R3, R4 have the above meanings, with an oxidizing
mixture consisting of osmium tetroxide and an alkaline or alka-
line-earth metal chlorate, in the presence of water.


2. Process according to claim 1, characterized in that
the reaction is carried out at temperatures of from 0 to 100°C.


3. Process according to claim 3, characterized in that
the reaction is carried out at temperatures of from +25 to +50°C.



4. Process according to claim 1, characterized in that
the reaction is carried out at a pressure under which the system
is in the liquid phase.


5. Process according to claim 1, characterized in that
the water is added with an inert solvent.


6. Process according to claim 1, further comprising
recovering osmium tetroxide.

Description

16~39750
- The present invention relates to a process for the
preparation of -diol -dioxo compounds having the general

formula:
R2 3 ~ -

R -CO-C - ~-co~R4
OH OH
in which R and R which may be identical or different, each
represent a lower alkyl radical and R and R3 each represent a hy-
drogen atom, which process comprises reacting a compound having

- the general formula
R2 R3
R _ co_1 - 1 co- R4
in whcih Rl, R2, R3, R4 have the above meanings, with an oxidizing
mixture of osmium tetroxide and an alkaline or alkaline-earth
chlorate, in the presence of water:
The ~-diol-~-dioxo compounds according to the present
invention are useful synthesis intermediates, for instance in the
preparation via cyclization of furane derivatives, some of which
may be employed as flavorants or perfumes / see G. B~chi, E. Demo-

le and F. Thomas, I. Org. Chem. 38, 123 (1973) and L. Re, B. Maurer,
G. Ohlaff, Helv. 56, 1882 (1973)7. Compared to the known methods


of preparation of the aforesaid~-diol-~-dioxo compounds, the
method according to the invention has the advantage of being
not only cheaper but also simpler form an operative point
of view.
Furthermore, in the preparation of furane derivatives
through cyclization, the method according to the invention of
synthesis of ~-diol-~-dioxo compounds is particularly interesting


. : ~ , . ;. ~.
;;~ since it enables the cyclization, through kno~ operations (see

already cited G. B~chi et al.), of the aqueous mixture obtained
at the end of the reaction, after recovery of osmium tetroxide, ~-
without isolating the intermediate compound. ~

' 16)39750 , ...
According to the invention, the oxidizing agent
,
comprises osmium tetroxide. This compound can be used in cataly-
tic amounts preferably of at least 20 mg per g of substrate, -
since it is continuously regenerated by the chlorate through an
oxidative scission of the adduct between osmium tetroxide and ~ -
substrate. Chlorate must, therefore, be also present in at least
stoichiometric amounts.
In accordance with the invention, osmium tetroxide
: .
may be recovered at the end of the reaction by dragging under a
., .
nitrogen stream, osmium tetroxide being caught in a trap contain-
; 10 ing the starting product with which it forms a non-volatile
adduct, or by selective extraction by means of a suitable solvent
` such as CC14, benzene, Et2O and subsequent solvent evaporation
after having add the extract to the starting products, or also
by another techniques well known to any man skilled in the art.
The oxidation reaction is carried out in an aqueous

environment at a temperature ranging from 0 to 100C, preferabl~3
from t25 to ~50C and under pressure to maintain the system in
the liquid phase. When use is made of water unsoluble solid
~ ~ substrate, use is preferably made of an inert usual solvent
:~
either miscible with water fro dissolving, at least partially,
the substrate (THF, alcohols) or immiscible with water for
I dissolving, also only partially, both the substrate and osmium
.~; , . .
tetroxide (CC14, Et2O, benzene).

The present invention will be better understood with

reference to the following non-restrictive examples.

~ I EXAMPLE 1.


; ~ PreParation of treo-3,4-dihYdroxYhexane-2,5-dione from
. ::
~` ~ trans-3-hexene-2,5-dione

To 15 ml of water were added 0.79 g (6.45 mmoles)

of potassium chlorate, 250.4 mg (O.lO mmole) of osmium tetroxide

and 0.50 g (4.46 mmoles) of trans-3-hexPne-2,5-dione. The mixture

- 2 -

~3~750
was stirred over 17 hours at room temperature in a closed vessel.
The water-insoluble liquid phase was extracted with dimethylfu-
rane. To recover osmium tetroxide, nitrogen was bubbled through
the reaction vessel connected, at its outlet, to a trap provided
with a porous septum immersed in diemthylfurane and cooled. The
osmium tetroxide, dragged by nitrogen, was caught through
~ formation of an adduct with hexenedione, that is not volatile.
; The content of the trap could be used, after addition of water
and potassium chlorate, for another preparation.
; The reaction mixtùrewas dry evaporated under a 15 mmHg
-;~ 10 vacuum at room temperature. The residue was extracted several
times with ethyl acetate and the extracts, joined together, were
; dried (anhydrous sodium sulphate) and dry evaporated under vacuum.
0.51 g of a raw product was obtained, which, after having been
again crystallized from ligroin, gave 0.31 g (47.6~ yield) of
pure treo-3,4-dihydroxyhexan-2,5-dione, having a melting point
of 88-90C. The obtained infrared and NMR spectra agreed with the ~
known ones (G. B~chi et al.) ;
~ EXAMPLE 2.
;~ Preparation of eritro-3,4-dihydroxyhexane-2,5-dione
~, .
from cis-3-hexene-2,5-dione
To 6 ml of water were added 0.25 g (2.05 mmoles) of i~
j potassium chlorate, 10.2 mg (0.04 mmole) of osmium tetroxide
q~ and 0.20 g (1.78 mmoles) of cis 3-hexene-2,5-dione. The mixture
was stirred at room temperature for 6 hours in a closed vessel.
i Osmium tetroxide was recovered by selective extraction
' with carbon tetrachloride, followed by the addition of hexenedione ~ ;
to the extract, so as to form a non-volatile adduct between the
~ olefin and osmium tetroxide, and by a solvent evaporation. The
I evaporation ~esidue could then be used, after addition of water ~;
and potassium chlorate, for another preparation.
The reaction mixture was dry evaporated under vacuum

~ 3 ~




,, . . ... . . . . - ~ .

1~)39750
(15 m~g) at room temperature. The residue was extracted several
times with ethyl acetate and the extracts, joined together, were
dried (anhydrous sodium sulphate) and dry evaporatèd under
vacuum. 0.20 g of a white crystalline products was obtained
having a melting point of 48-51C. Via crystallization from
chloroform-carbon tetrachloride (1:1), 0.13 g (50~ yield) of
pure eritro-3,4-dihydroxyhexane-2,5-dione was obtained having
a m.p. of 56-60 C, and IR and NMR spectra agreeing with the
known ones (G. B~chi et al.).




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