Sulfines, a unique class of sulfur-centered heterocumulenes†

The chemistry of sulfines (thione S-oxides) is briefly reviewed with focus on highlights and milestones. Sulfines can conveniently be prepared by oxidation of a large variety of thiocarbonyl-containing compounds. Alkylidenation of sulfur dioxide with alpha-silyl carbanions is an attractive method of preparation as it allows access to sulfines that cannot be obtained by the oxidation method. The reaction of activated methylene compounds with thionyl chloride is a highly versatile method of preparation. The scope of the reaction with thionyl chloride is extended by using silyl enol ethers and silyl ketene acetals as starting materials. The cycloaddition reaction of sulfines with 1,3-dienes is widely used for trapping purposes. The DielsAlder type cycloadducts are useful compounds in synthesis. Dipolar cycloaddition reactions are of interest as well as the addition reaction of alkyllithium regents. O-Alkylation of aminosulfines gives iminosulfenates which are of interest for further synthetic elaboration.