General and efficient I2/DMSO mediated synthesis of chalcogenated indolo[1,2-a]quinoxalines through direct and indirect methodologies

A versatile protocol for the regioselective Csp2–H chalcogenation of indolo[1,2-a]quinoxaline derivatives through I2/DMSO-catalyzed cross-dehydrogenative coupling (CDC) utilizing arylthiols/arylselenols at 80 °C has been established. This C–H functionalization proceeds selectively at the C3-position of indole fragment embedded in indolo[1,2-a]quinoxaline hybrids integrated with various pharmacologically active units, namely aryl, benzoyl, benzoyl ester and phthalazinones. This robust iodine-catalyzed metal-free technique where DMSO acts as oxidant as well as solvent exhibited broad functional group tolerance and enabled the synthesis of diversely decorated sulfenylated/selenylated indolo[1,2-a]quinoxalines under mild reaction conditions within a short reaction time. Interestingly, these chalcogenated indoloquinoxaline hybrids can be achieved via a regioselective cascade C-H activation through two possible reaction pathways, one involving C-insertion followed by chalcogenation (direct) and the other one involving chalcogenation followed by C-insertion (indirect).