Selective one-pot synthesis of 11-arylmethylidene-11H-isoindolo-[2,1-a]benzimidazoles and 6-arylbenzimidazo[2,1-a]isoquinolines from o-alkynylbenzaldehydes and o-diaminobenzenes

Cyclization of o-alkynylbenzaldehydes with o-diaminobenzenes in DMSO under the sequential action of NH4Br and K2CO3 affords 11-arylmethylidene-11H-isoindolo[2,1-a]-benzimidazoles as a result of 5-exo-dig ring closure; whereas replacement of treating with K2CO3 by heating at 110–115°C results in 6-endo-dig cyclization with formation of 6-arylbenzimidazo[2,1-a]isoquinolines.