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