Unexpected formation of pyrrolo[1,2-a]quinoxaline derivatives during the multicomponent synthesis of pyrrolo[1,2-a]benzimidazoles

New pyrrolo[1,2-a]benzimidazole and pyrrolo[1,2-a]quinoxaline derivatives are obtained via one-pot, three-component reactions from 1-benzylbenzimidazoles, α-bromocarbonyl compounds, and non-symmetrical activated acetylenic dipolarophiles in propylene oxide as both the reaction medium and acid scavenger, at room temperature. When the same reaction is performed in 1,2-epoxybutane at reflux temperature only the pyrrolo[1,2-a]benzimidazole derivative is obtained.