Stereospecific Synthesis of (Z)-1,3-Oxazolobenzimidazoles from Imidazole- and Benzene-Ring-Substituted Benzimidazoles and α,β-Acetylenic γ-Hydroxynitriles

A stereospecific, facile synthesis of (Z)-1,3-oxazolobenzimidazoles from imidazole- and benzene-ring-substituted benzimidazoles and α,β-acetylenic γ-hydroxynitriles has been elaborated. The reaction proceeds smoothly in acetonitrile without catalyst (room temperature, 3-5 days or 35-40 °C, 20-72 h) to afford the target compounds in 33-90% yields. The annulation involves an intermediate vinyl carbanion with zwitterionic character, which, after transformation into an O-centered zwitterion, is further inserted into the aromatic system of the imidazole ring. The synthesis contributes to the basic benzimidazole and acetylene chemistry and drug design.