Visible-Light Photoredox-Catalyzed Radical Addition/Cyclization of Imidazoles with Alkenes: Access to Polycyclic Imidazoles Bearing Alkylsulfonyl or Exocyclic Olefin Units

A metal-free visible-light photoredox-catalyzed one-pot tandem synthesis of alkylsulfonyl-containing polycyclic imidazoles from easily accessible <i>N</i>-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.