Photoinduced synthesis of (E)-vinyl sulfones through the insertion of sulfur dioxide

Under visible light irradiation, a three-component reaction of potassium alkyltrifluoroborates, sulfur dioxide and alkynes with the assistance of photocatalysis and in the presence of copper(II) triflate is described. This transformation affords (E)-vinyl sulfones efficiently with excellent regioselectivity and stereoselectivity under mild conditions. Various functional groups including acetyl and thiophenyl groups are tolerated. The photocatalysis facilitates the formation of an alkyl radical, which initiates the transformation with the insertion of sulfur dioxide. The presence of the copper catalyst assists the addition of an alkylsulfonyl radical to alkyne, thus leading to (E)-vinyl sulfones.