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

Abstract

Convenient access to 6‐alkylsulfonylmethyl phenanthridines has been demonstrated both under non‐catalytic thermal and visible‐light photoredox‐catalyzed conditions. A cascade of radical cyclization is triggered by the 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.