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.