A Versatile Method for the Synthesis of Benzimidazoles from o-Nitroanilines and Aldehydes in One Step via a Reductive Cyclization

ABSTRACT A highly efficient and versatile method for the synthesis of benzimidazoles was achieved in one step via the Na 2 S 2 O 4 reduction of O-nitroanilines in the presence of aldehydes. Heating a solution of O-nitroaniline (1C) and an aldehyde in EtOH or another appropriate solvent, in the presence of aqueous or solid Na 2 S 2 O 4 , provided facile access to a series of 2-substituted N-H benzimidazoles 5A-M containing a wide range of functional groups not always compatible with the existing synthetic methods. This methodology has also been applied to the regioselective synthesis of N-alkyl and N-aryl benzimidazoles 6A-F via the cyclization of the corresponding N-substituted nitroanilines 13A-E, respectively. In addition, the method was applied successfully to the synthesis of other imidazole containing heterocyclic ring systems such as 1H-imidazo[4,5-b]pyridines 14A,B and 1H-imidazo[4,5-f]quinoline 15.