Synthesis of 1,2-disubstituted benzimidazoles through DDQ-oxidized intramolecular dehydrogenative coupling of N,N′-dialkyl o-phenylenediamines

Abstract The synthetic methodology of 1,2-disubstituted benzimidazoles has been developed, which starts from N,N′-dialkyl o-phenylenediamines via intramolecular dehydrogenative coupling under the oxidation of DDQ with mild conditions. Through detailed optimization of reaction conditions, only DDQ was found essential without any additives to reach to the highest yield of 99%. In the cases of linear aliphatic substituents, the synthesis of 1-alkyl-2-phenylbenzimidazoles showed high selectivities and their structures were identified by 2D NMR COSY correlation analysis. A plausible mechanism was proposed to interpret the observed reactivities and selectivities.