Photoinduced synthesis of alkylalkynyl sulfones through a reaction of potassium alkyltrifluoroborates, sulfur dioxide, and alkynyl bromides†
A photoinduced reaction of potassium alkyltrifluoroborates, sulfur dioxide, and alkynyl bromides under visible light irradiation at room temperature is developed, giving rise to alkylalkynyl sulfones in moderate to good yields. This transformation works well under photocatalysis with broad substrate scope by using sodium metabisulfite as the source of sulfur dioxide. Mechanistic studies show that the reaction is initiated by an alkyl radical generated in situ from potassium alkyltrifluoroborate in the presence of a photocatalyst. Then sulfonylation occurs through the insertion of sulfur dioxide to provide an alkylsulfonyl radical intermediate, which reacts with alkynyl bromide, leading to the corresponding alkylalkynyl sulfone.