Intramolecular cyclization of (allylthio)sulfines via their vinylsulfenic acid tautomers

Intramolecular cyclization of enethiolizable (allylthio)sulfines afford 2-alkylidene-1,3-dithiolane-1-oxides in good yields. The formation of these compounds can be explained by an initial tautomerization of the sulfine to vinyl sulfenic acid, followed by an intramolecular addition of the sulfenic acid to the allylic double bond. The stractures of the products were elucidated by means of 1H-and 13C-NMR spectroscopy as well as LIS effects, deuteriation experiments and an X-ray analysis.