Formation of N-Heterocycles from 1,1-Diethoxy-5-hydroxyalk-3-yn-2-ones

Abstract

When treated with hydrazine, guanidine, and hydroxylamine, 1,1-diethoxy-5-hydroxyalk-3-yn-2-ones undergo Michael addition and give the corresponding β,β-disubstituted α,β-unsaturated olefinic ketones, which are unstable and undergo secondary reactions to form heterocyclic compounds. Hydrazine affords 3,5-disubstituted pyrazoles and hydroxylamine 5-hydroxy-4,5-dihydroisoxazoles in very good yields. Guanidine, however, furnishes complex reaction mixtures, which include the corresponding 2-aminopyrimidines. These results show that cyclization involves attack of the ketone moiety by the bisnucleophile reactive terminal group and not the hydroxyl group present in the starting material.

Key words

α,β-unsaturated alkynones - hydrazine - guanidine - hydroxylamine - Michael addition - pyrazole - dihydroisoxazole - pyrimidine

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