The synthesis and properties of pyrrolo [1,2-a]pyrazines are reviewed. Some derivatives of pyrrolo[1,2-a]pyrazine possess neuroleptic, cardiovascular [1], and antidepressant [2] activity. Alkylated pyrrolo[1,2-a]pyrazines have been identified as ingredients of the smell of roasted meat [3]. Interest for this class of compounds is determined mainly by the wide range of their physiological activities. Also, they are of interest in food chemistry. The aim of this review article is to give an overview and summary of the existing methods for the preparation of pyrrolo[ 1,2-a]pyrazines that should be useful in the development of new synthetic approaches. Two short reviews on the synthesis and properties of pyrrolo[1,2-a]pyrazines have been published earlier [4,5], but a number of new original papers have appeared since then.
In the pyrrolo[ 1,2-a]pyrazine system, the condensed pyrrole and pyrazine rings share one nitrogen atom. The syntbetie approaches to these compounds can be divided into three groups:
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Construction of a pyrrole ring onto an existing pyrazine one.
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Construction of a pyrazine ring onto an existing pyrrole one.
3. Consecutive formation of the pyrrole and pyrazine rings.
A number of derivatives of pyrrolo[1,2-a]pyrazine can also be prepared by dehydrogenation of the corresponding polyhydrogenated compounds. In this review, only a few methods for the preparation of polyhydrogenated derivatives of this class of compounds are presented, since their synthesis is itself an interesting and important topic of organic chemistry [5].
METHODS FOR THE SYNTHESIS OF PYRROLO[1,2-a]PYRAZINES
- Construction of a Pyrrole Ring onto an Existing Pyrazine One 9 This is the most general group of synthetic approaches. The starting compounds used here are usually Nand 2-substituted pyrazines. A pyrrole ring can be formed by a number of different routes: J J Z 3 4 5 1.1. Unsubstituted pyrazine or its 2-methy! and 2,6-dimethyl derivatives react with diphenylcyclopropenone [6] and diphenylcyclopropenethione [7], producing a number of derivatives of pyrrolo[1,2-a]pyrazine. Compound Me Ph Ph !