A metal-free visible-light photoredox-catalyzed one-pot tandem synthesis of alkylsulfonyl-containing polycyclic imidazoles from easily accessible N-alkenyl imidazoles, DABCO(SO2)2 and 4-alkyl Hantzsch esters, has been developed. Operating under mild conditions, this method affords high yields for a wide range of substrates, exhibits remarkable functional group tolerance, and can be readily scaled up. The observed catalytic efficiency stems from employing cheap and readily available organic dye Eosin Y as a photocatalyst and economical (NH4)2S2O8 as an oxidant. Moreover, the synthetic utility of this protocol is further showcased by its application in the efficient synthesis of exocyclic alkenes.
Wang et al. (Wed,) studied this question.