Fine tuning the outcome of 1,3-dipolar cycloaddition reactions of benzimidazolium ylides to activated alkynes

Abstract 1,3-Dipolar cycloaddition reactions of benzimidazolium ylides, generated from 3-phenacylbenzimidazolium bromides, to non-symmetrical activated dipolarophiles in various reaction conditions led to complex mixtures of pyrrolo[1,2- a ]benzimidazole and pyrrolo[1,2- a ]quinoxaline derivatives. In order to explain all experimental results, the influence of reaction conditions on the reaction products was investigated. For the first time, 4-hydroxy-4,5-dihydropyrrolo[1,2- a ]quinoxaline derivatives 6 , pyrrolo[1,2- a ]quinoxalinium quaternary salts 8 , as well as 4-methoxy-4,5-dihydropyrrolo[1,2- a ]quinoxalines 9 , were separated, fully characterized and their interconversions are presented, together with a proposed reaction mechanism.