Photoredox-Catalyzed Radical Heterocyclization of Heteroatom-Tethered Alkenes with α-Iodonium Diazo Compounds.

A photoredox-catalyzed radical heterocyclization of alkenoic acids and sulfonamides with α-iodonium diazo compounds is reported. The reaction delivers diazomethyl-containing lactones and pyrrolidines in good yields with full retention of the diazo group. The synthetic utility is demonstrated by a gram-scale synthesis and downstream derivatizations under mild, redox-neutral conditions. A plausible radical-polar crossover mechanism is proposed for this transformation.