Photoredox-catalyzed hydrosulfonylation reaction of electron-deficient alkenes with substituted Hantzsch esters and sulfur dioxide

A sulfonylation reaction of 4-substituted Hantzsch esters, DABCO center dot(SO2)(2), and electron-deficient alkenes at room temperature in the presence of photoredox catalysis under visible light irradiation is described. Not only (E)-chalcones but also (vinylsulfonyl) benzene and 2-vinylpyridine are all suitable substrates in the transformation. This sulfonylation reaction under mild conditions shows a broad substrate scope with a good functional group compatibility. A plausible mechanism is proposed, which shows that the 4-substituted Hantzsch esters would be radical reservoirs under photoredox catalysis. The alkyl radical generated in situ from the 4-substituted Hantzsch ester would be trapped by sulfur dioxide to produce an alkylsulfonyl radical, which would then undergo further transformation leading to the final outcome.