Synthesis of 9-Substituted Imidazo[1,2-a]benzimidazoles Containing a 5-Nitrofuran-2-yl Fragment

9-Substituted 2-(5-nitrofuran-2-yl)-9H-imidazo[1,2-a]benzimidazoles were synthesized for the first time by cyclization of quaternary salts obtained from 1-substituted benzimidazol-2-amines and 2-bromo-1-(5-nitrofuran-2-yl)ethan-1-one. 9-R-2-Methyl(aryl)-9H-imidazo[1,2-a]benzimidazoles reacted with 5-nitrofuran-2-carbaldehyde and 4-nitrobenzaldehyde to give the corresponding secondary alcohols as a result of aldehyde addition to the 3-position of the tricyclic system. The Witting olefination of ethyl 2-(bromomethyl)-9-methyl-9H-imidazo[1,2-a]benzimidazole-3-carboxylate afforded 2-ethenylimidazo[1,2-a]benzimidazoles.