Stereoselective one-pot synthesis of (1Z)- and (1E)-1-arylmethylidene-2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazoles by cyclization of alk-4-ynals with o-diaminobenzene

Cyclization of alk-4-ynals with o-diaminobenzene in DMSO under the sequential action of NH4Br and base (KOH or K2CO3) affords l-arylmethylidene-2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazoles, which are formed selectively as E- or Z-isomers depending on the base used.