Vicinal Difunctionalization of Alkenes through a Multicomponent Reaction with the Insertion of Sulfur Dioxide

A four-component reaction of aryldiazonium tetrafluoroborates, sulfur dioxide, alkenes, and hydroxylamines under mild conditions is accomplished. No catalyst or additive is needed for the vicinal difunctionalization of alkenes with the insertion of sulfur dioxide. Not only DABCO⋅(SO₂ )₂ (DABCO=1,4-diazabicyclo[2.2.2]octane) but also potassium metabisulfite (K₂ S₂ O₅ ) is effective in this transformation. The multicomponent reaction proceeds efficiently at room temperature with broad substrate scope, leading to the corresponding products in good yields.