Pyrazine chemistry. Part V. Diels-Alder reactions of some 2,5-dihydroxypyrazines

Abstract

Certain 2,5-dihydroxypyrazines and related systems undergo 1,4-cycloaddition reactions. Dimethyl acetylenedicarboxylate reacts to give bicyclic adducts which readily undergo a retro-Diels-Alder reaction with elimination of cyanic acid and formation of substituted pyridones. 5-Ethoxy-1,3-dimethylpyrazin-2-one (16) has been synthesised and shown to undergo ready cycloaddition reactions even with non-activated double bonds. The implications of these reactions relative to the biosynthesis of the mould metabolite brevianamide A and related compounds are discussed.