Metal-free insertion of sulfur dioxide with aryl iodides under ultraviolet irradiation: direct access to sulfonated cyclic compounds

Metal-free insertion of sulfur dioxide with aryl iodides and silyl enolates or allylic bromide under ultraviolet irradiation at room temperature is accomplished. This protocol provides a convenient route to sulfonated cyclic compounds under mild conditions. Not only N-(2-iodophenyl)-N-methylmethacrylamides but also 1-iodo-2-allenoxybenzene is workable. A plausible mechanism is proposed, which shows that during the reaction process, aryl radicals formed in situ from aryl iodides under ultraviolet irradiation undergo intramolecular 5-exo-cyclization, with subsequent sulfonylation via insertion of sulfur dioxide. The resulting sulfonyl radicals are further trapped by silyl enolates or allylic bromide giving rise to sulfonated cyclic compounds.