Transition‐metal‐free Photo‐induced Cascade Sulfonylation/Addition/Cyclization of 3‐Arylethynyl‐[1,1′‐biphenyl]‐2‐carbonitriles with Aryldiazonium Tetrafluoroborates via the Insertion of Sulfur Dioxide

Abstract A transition‐metal‐free photo‐induced cascade sulfonylation/addition/cyclization of 3‐arylethynyl‐[1,1′‐biphenyl]‐2‐carbonitriles with Na 2 S 2 O 5 and aryldiazonium tetrafluoroborates for the construction of 4‐sulfonated cyclopenta[ gh ]phenanthridines is developed. This reaction involves a radical pathway and goes through a sequence of phenyl radical formation, sulfur dioxide insertion, sulfonyl radical addition, iminyl radical formation, and cyclization. The methodology displays mild conditions, a broad substrate scope and does not require any external oxidants. magnified image