Unusual cleavage of phenacyl-substituted benzimidazolium salts. Synthesis of 1,4-diarylimidazoles

The action of ammonium acetate in acetic acid on 1-alkyl(aralkyl)-3-phenacylbenzimidazolium bromides leads, in addition to the formation of a new imidazole ring, to cleavage of the benzimidazole fragment of the molecule at the 1,2 bond to give 1-alkyl(aralkyl)aminoaryl-4-arylimidazoles. 1,2-Dimethyl-3-(p-nitrophenacyl)benzimidazolium bromide is converted under similar conditions to the corresponding 2-methylimidazole. 4,4-Dimethyl-2,2-bis(p-nitrophenyl)-1,1-dipyrrolo[1,2-a]benzimidazole was isolated as a side product of this reaction.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 388–392, March, 1982.