Iron-catalyzed [3 + 2 + 1] annulation of 2-aminobenzimidazoles/3-aminopyrazoles and aromatic alkynes using N , N -dimethylaminoethanol as a one carbon synthon for the synthesis of pyrimido[1,2- a ]benzimidazoles and pyrimido[1,2- b ]indazoles

A simple and efficient method for the synthesis of pyrimido[1,2- a ]benzimidazoles and pyrimido[1,2- b ]indazoles from 2-aminobenzimidazoles/3-aminoindazoles, alkynes and N , N -dimethylaminoethanol by a three-component [3 + 2 + 1] annulation catalyzed by FeCl 3 has been established, where N , N -dimethylaminoethanol was applied as a methine source. Good tolerance of the reaction makes this method applicable to construct biologically active pyrimido[1,2- a ]benzimidazoles and pyrimido[1,2- b ]indazoles. In addition, regioselective aryl substituted pyrimido[1,2- a ]benzimidazoles were synthesized in the presence of TfOH. Replacement of alkynes with acetaldehydes gave the same pyrimido[1,2- a ]benzimidazoles and pyrimido[1,2- b ]indazoles.