Process for the preparation of substituted pyrazines

Details Process for the preparation of substituted pyrazines Process for the preparation of substituted pyrazines

1995-12-15

1997-10-21

Bernhardt, Emily

Organic compounds -- part of the class 532-570 series

Organic compounds

Nitrogen attached directly or indirectly to the purine ring...

544336, 544354, 544410, C07D24112, C07D24138

Patent

active

056797931

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/IB95/00212 filed Mar. 28, 1995.


TECHNICAL FIELD

The present invention relates to the field of organic synthesis and, more particularly, to that of the preparation of substituted pyrazines.
The substituted pyrazines, and in particular alkylpyrazines, are very important flavoring ingredients, mostly of natural origin. Namely, they are present in a great many fermented products or in products which undergo a thermal treatment.
On the other hand, these alkylpyrazines are also useful as starting products for the preparation of other pyrazine derivatives and thus play an important role in organic synthesis.


PRIOR ART

Processes for the preparation of alkylpyrazines are already known, which are particularly adapted to the synthesis of natural products. For example, G. P. Rizzi, in J. Agr. Food Chem 36, 349 (1988), describes a process for the preparation of alkylpyrazines via the reaction of acyloins with ammonium acetate, under so-called "soft" reaction conditions. This process requires a complex procedure, with a long reaction time.
On the other hand, in European patent application n.sup.o 505 891, there is disclosed a process which makes use of the same reaction, but wherein the latter is carried out at reflux in water, if need be with simultaneous sublimation of the reaction mixture.
These two processes enable the preparation of symmetrical alkylpyrazines, but do not provide a satisfactory solution to the problem of the preparation of asymmetrical substituted pyrazines, which preparation is known to be far more difficult.


DESCRIPTION OF THE INVENTION

The aim of the present invention is precisely to provide a novel solution to this problem, by realizing a process of very general application which makes it possible to obtain substituted pyrazines, of natural or synthetic origin, and in particular asymmetrical alkylpyrazines. Thus, the invention relates to a process for the preparation of a pyrazine of formula ##STR3## wherein A=B=C=D=R.sup.1 =R.sup.2, or wherein A=C=R.sup.1, B=D=R.sup.2, and R.sup.1 .noteq.R.sup.2, or A=D=R.sup.1, B=C=R.sup.2 and R.sup.1 .noteq.R.sup.2, symbols R.sup.1 and R.sup.2 representing each a hydrogen atom, a saturated or unsaturated, linear or branched, hydrocarbon radical having 1 to 6 carbon atoms or a --CH.sub.2 OH group; or respectively of formula ##STR4## wherein A'=R.sup.3, B'=R.sup.4 or vice versa and C'=R.sup.1, D'=R.sup.2, R.sup.1 and R.sup.2 being identical or different and having the above-mentioned meaning and R.sup.3 and R.sup.4 being identical or different and representing each a C.sub.1 to C.sub.6, saturated or unsaturated, hydrocarbon radical, or a saturated or unsaturated cyclic radical, substituted or unsubstituted, having 5 or 6 carbon atoms in the ring, or being identical and representing a CH or CH.sub.2 group belonging to a ring such as indicated by the dotted line, containing 5 or 6 carbon atoms, substituted or unsubstituted, the process being characterized by the reaction, in an inert organic solvent, of a compound of formula ##STR5## wherein R.sup.1 and R.sup.2 are identical or different and have the meaning indicated above, with an ammonium salt, or respectively with an ammonium salt and an acyloin of formula ##STR6## wherein R.sup.3 and R.sup.4 have the meaning indicated in formula (IV) and, if need be, by the separation of said pyrazine from the reaction product.
The process of the invention is based on the principle of the use of formula (I) dihydroxyketone as a substrate which reacts with the ammonium salt. Without wanting to prejudge on the mechanism of the reaction, it is possible that this dihydroxyketone self-reacts or reacts with the acyloin of formula (III) to form the (di)-hydroxymethyl-dihydropyrazines, the latter undergoing spontaneous dehydration to yield the desired substituted pyrazines. Thus, in the particular case of 1,3-dihydroxy-2-propanone, its self-reaction yields the hydroxypyrazine represented in the following scheme: ##STR7##
Furthermore, formation of 6-methyl-2-pyrazinemethanol, albeit in a less

REFERENCES:
patent: 3544682 (1970-12-01), Taylor et al.
patent: 3928352 (1975-12-01), Taylor
Chemical Abstracts, vol. 88, No. 15, 1978, Abstract No. 88: 105411e, p. 582; column 2.
Rizzi, George P., "Formation of Pyrazines from Acyloin Precursors under Mild Conditions", J. Agric. Food Chem. 11988, 36, pp. 349-352.

Affiliated with

Also associated with

Rating

Process for the preparation of substituted pyrazines does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Process for the preparation of substituted pyrazines, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the preparation of substituted pyrazines will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1007727