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

COMPOSES .alpha.-DIOL .gamma.-DIOXOIQUES

English Abstract

ABSTRACT OF THE DISCLOSURE:
The invention relates to a process for the preparation
of -diol- -dioxo compounds having the general formula:
<IMG>
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:
<IMG>
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 or perfumes.

Claims

The embodiments or the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. Process for the preparation of .alpha.-diol-?-dioxo
compounds having the general formula:
<IMG>
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, which process comprises reacting a compound
having the general formula
<IMG>
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.
2. Process according to claim 1, characterized in that
the reaction is carried out at a temperature of from 0 to 100°C.
3. Process according to claim 3, characterized in that
the reaction is carried out at a temperature 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 liquid
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

~o39749 ~
The present invention relates to a process for the
preparation of ~-diol-~-dioxo compounds having the general
; formula
R R3
Rl-CO-l -- C -Co-R4 , .. .
.. 1H 1H
in which R and R4, which may be identical or different, each
represent a lower alkyl radical and R2 and R3 each represent
a hydrogen atom, which process comprises reacting a compound
having the general formula:
R ~ R4
.;,,' ' ,
in which R1, R2, R3, R4 have the abovesaid meanings, with an
'~4~i oxidizing mixture consisting of osmium tetroxide and an alkaline
or alkaline-earth chlorate, in the presence of water. The
~ ~-diol-~-dioxo compounds according to the present invention
3 are useful syntesis intermediates, for instance in the prepara-
tion via cyclization of furane derivatives, some of which may
be employed a9 flavorants and per~umes ~see G. B~chi, E. Demole
and F. Thomas, I. Org. Chem. 38, 123 (1973) and L. Re, B. Maurer,
; ~. Ohlaff, Helv. 56, 1882 ~1973)). 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 from an operative point of
view.
Furthermore, in the preparation of furane derivatives
through cyclization, the method of synthesis of the ~-diol-~
dioxo compounds according to the invention is particularly
nteresting since it enables the cyclization, through known

1039749 :
operations (see the already cited G. B~chi et al.) of the -~
aqueous mixture obtained at the end of the reaction after ~1
recovery of osmium tetroxide, without isolating the intermediate
compound.
According to the invention, the oxidizing agent
comprises osmium tetroxide. This compound can be used in cata-
lytic 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 present invention, osmium
, tetroxide may be recovered at the end of the reaction by dragging
under a nitrogen stream, the osmium tetroxide being caught
A`i in a trap containing 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
~1 20 skilled in the art.
The oxidation reaction i5 carried out in an aqueous
environment at a temperature ranging from 0 to 100C, preferably
~ ~ .
from ~25 to ~50C and under pressure to maintain the system in
the liquid phase. When use is made of a water unsoluble solid
` substrates, use is preferably made of an inert usual solvent
j either miscible with water for dissolving, at least partially,
7 , the substrate (THF, alcohols) or immiscible with water for
dissolving, also only partially, both substrate and osmium '
tetroxide (CC14, Et2O, benzene).
The present invention will be better understood
~ with reference to the following non~restrictive example
-~ EXAMPLE
; - 2 -
`',~,~ . ' ''" '" '

~Q;~9749
Preparation of eritro-3,4-dihydroxy~xan~2/5-dione from 2,5-
dimethylfurane:
To 30 ml of water were added 2.80 g (22~8 mmo~les) of
potassium chlorate, 50.8 mg (0.20 mmole) of osmium tetroxide
and 0.96 g (lO.0 mmoles) of 2.5-dimethyl furane. The mixture
was stirred over 17 hours at room temperature in a closed
vessel. The water insoluble liquid phase was extracted with
dimethylfurane. 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 dimethyl-
furane and cooled. The osmium tetroxide, dragged by nitrogen,
was caugth through formation of dimethylfurane adduct, that is
not volatile. The content of the trap could be used, after
addition of water and potassium chlorate, for another prepara-
tion. Alternatively the osmium tetroxide recovery could be
carried out by means of a selective extraction t;ereof with
~i CCl4 followed by the addition of dimethylfurane to the extract
so as to form an adduct, and by a solvent distillation. The
' distillation residue could then be used after addition of water
and potassium chlorate, for another preparation.
The reaction mixture was dry evaporated under a 15
mmHg vacuum at room temperature. The re~idue was extracted se-
veral times with ethyl acetate and the extracts, joined
; together, were dried (anhydrous sodium sulphate) and dry evapo-
rated under vacuum. 1.26 g. of a white crystalline product
were obtained having a melting point of 46 - 49C, from which
' was obtained 0.89 g (61% yield) of pure eritro-3,4-dihydroxy-
;~. hexan-2,5 dione, via chlorofom-ligroin crystallization,
it having a melting point of 60-62 C and infrared and NMR
spectra agreeing the known ones (G. B~chi et al.)
,. ~, .
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