Thermal vs. Visible-Light Photoredox-Catalyzed Cascade Radical Cyclization Involving SO2 Fixation to Access 6-Alkylsulfonylmethyl Phenanthridines

Convenient access to 6-alkylsulfonylmethyl phenanthridines has been demonstrated both under thermal and visible-light photoredox-catalyzed conditions. A cascade of radical cyclization is triggered on exposure of biphenyl vinyl azides to the in-situ generated alkyl sulfonyl radicals from 4-substituted Hanztsch esters in the presence of an SO2 surrogate. Transition metal-free, mild reaction conditions, and broad substrate scope constitute some of the highlights of the approach. Also, the synthetic utility of the accessed 6-alkylsulfonylmethyl phenanthridines has been demonstrated.