Dihydrobenzimidazole chemistry. Part IV. Acid-catalysed reactions of anils and dihydrobenzimidazoles

Abstract

Aldehyde anils of o-dialkylamino-o-piperidino-, o-morpholino-, and o-perhydroazepino-aniline are shown to yield equal proportions of the corresponding N-alkylanilines and benzimidazolium salts when treated with acid in cold ethanol solution. These products are shown to arise by cyclisation of the anil to a dihydrobenzimidazole followed by a bimolecular disproportionation involving hydride-transfer. The difference in behaviour of the pyrrolidino- and other anils towards acid is discussed. The formation of stable dihydrobenzimidazoles bearing an NH group is demonstrated.