Photocatalytic Reaction of Potassium Alkyltrifluoroborates and Sulfur Dioxide with Alkenes.

A three-component reaction of potassium alkyltrifluoroborates, the sulfur dioxide surrogate of DABCO·(SO2)2, and alkenes under photocatalysis in the presence of visible light is developed. This reaction works efficiently at room temperature with the insertion of sulfur dioxide under mild conditions, affording diverse sulfones in good to excellent yields. The alkyl radical and alkylsulfonyl radical are generated as key intermediates, and a reductive single-electron transfer is involved in the reaction process.