The selective synthesis of -arylbenzene-1,2-diamines or 1-arylbenzimidazoles by irradiating 4-methoxy-4'-substituted-azobenzenes in different solvents.

The solvent-controllable photoreaction of 4-methoxyazobenzenes to afford 1-aryl-1-benzimidazoles or -arylbenzene-1,2-diamines has been studied. The irradiation of 4-methoxyazobenzenes in DMF containing 0.5 M hydrochloric acid provided -aryl-4-methoxybenzene-1,2-diamines as the major product, while irradiation in acetal containing 0.16 M hydrochloric acid led to 1-aryl-6-methoxy-2-methyl-1-benzimidazoles as the major product. A possible reaction mechanism explaining the selectivity was also discussed.