New method for in situ generation of enolate-iminium 1,4-dipoles for [4 + 2] and [4 + 1] dipolar heterocycloaddition reactions

Abstract

Generation of hydrazoylketenes by thermal decomposition of N-(diphenylenamino)pyrrolediones is accompanied by 5-exo-trig ring closure to furnish a zwitterionic dihydropyrazolone species. In contrast to Lisowskaya's earlier report, we established that in most cycloaddition reactions such dihydropyrazolones react as 1,4-dipoles. This reactivity pattern was demonstrated in several [4 + 4]-homodimerizations and in a series of [4 + 2] and [4 + 1] cycloaddition reactions with various dipolarophiles.