Metal-Free Synthesis of (E)-Vinyl Sulfones via An Insertion of Sulfur Dioxide/1,5-Hydrogen Atom Transfer Sequence

A metal-free three-component reaction of propargyl alcohols, sodium metabisulfite, and aryldiazonium tetrafluoroborates under mild conditions is described. The reaction proceeds efficiently at room temperature without the need of any catalysts, affording the corresponding (E)-vinyl sulfones in moderate to good yields with excellent functional group tolerance. Preliminary mechanistic studies show that a vinyl radical-induced 1,5-hydrogen atom transfer process and functional group migration are involved, resulting in the cleavage of inert C-H and C-C bonds in sequence.