Reaction Of Methyl (e)-2-phenyl-1-azirine-3-acrylates With Hydrazines And Amidines. Synthetic And Mechanistic Implications

1-Azirines 2a-b react with hydrazine in methanol to produce hexahydropyrrolo[3,2-c]pyrazol-5-ones 3a-b. The process is suggested to involve intramolecular interception of an unstable 4-aminopyrazoline intermediate resulting from C=N bond cleavage. Reaction of 2a with phenylhydrazine similarly affords 3c. In dimethyl sulfoxide, on the other hand, formamidine, guanidine, and hydrazine afford imidazole 4, pyrimidines 5a-b, amino-s-triazine 6, or triazole 9 as a consequence of C-C bond cleavage in aziridine intermediate 8. The intermediacy of tautomers is proposed to account for the diversity of products in this case. © 1991 American Chemical Society.5617