New method for in situ generation of enolate-iminium 1,4-dipoles for [4 + 2] and [4 + 1] dipolar heterocycloaddition reactionsElectronic supplementary information (ESI) available: Experimental procedures, physico-chemical and spectral data. CCDC 1457141-1457145. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6ra21981k

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. Thermolysis of N -(diphenylenamino)pyrrolediones proceeds with formation of dihydropyrazolone 1,4-dipoles. [4 + 4] Homodimerizations and a series of [4 + 2] and [4 + 1] cycloadditions of these species with various dipolarophiles were investigated.