Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet-Spengler reaction

An efficient tandem approach for the selective synthesis of dihydroimidazo[1,5-a]quinoxalines 6a-g and imidazo[1,5-a]quinoxalines 7a-h by the reaction of 2-imidazolyl anilines 4a-c with aryl aldehydes 5a-k under mild reaction condition is described. Introduction of electron-releasing alkyl groups in substrate 4a-b was found instrumental for the success of the reaction.