Entry to Sulfonylated Phenanthridines via Strained Cyclic Alcohol/Thianthrenium Salt‐Derived Radicals and SO ₂ ‐Capture under Visible‐Light Photoredox Catalysis

An efficient access to 6‐( γ ‐ketoalkylsulfonyl)methyl phenanthridines and 6‐(arylsulfonyl)methyl phenanthridines has been demonstrated under visible‐light photoredox‐catalyzed conditions. Exposure of biphenyl vinyl azides to strained 3°‐cyclopropanols in the presence of Ru(bpy) 3 Cl 2 and SO 2 surrogate DABSO under blue‐LED irradiation triggers a cascade radical cyclization to provide entry to the γ ‐ketosulfones–tethered phenanthridines in moderate to good yields. On the other hand, entry to the 6‐(arylsulfonyl)methyl phenanthridines is demonstrated via a complementary cascade radical cyclization event involving biphenyl vinyl azides and thianthrenium salts in the presence of Na 2 S 2 O 5 and fac ‐Ir(ppy) 3 catalyst under blue‐LED irradiation. The efficiency of the developed reactions has been established through broad substrate‐scope studies, and the mechanistic proposal is backed by incisive mechanistic probing studies.