Light Promoted Synthesis of Quinoxalines and Imidazo[1,2-a]pyridines via Oxybromination from Alkynes and Alkenes

Light promoted two-step one-pot syntheses of quinoxalines and imidazo[1,2-a]pyridines from alkynes and alkenes, respectively under mild conditions are described. The conversions occur via the formation of alpha,alpha '-dibromo ketones or alpha-bromo ketones on irradiation with UV LED fluorescent black light (380-390 nm) in acetonitrile/water mixture. This protocol does not require sensitizer or catalyst or additives. This two-step protocol is a new entry of synthetic methods available for quinoxaline and imidazopyridine derivatives and offers wide functional group tolerance.