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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.

Several analogues of GR24 with modifications in the ABC part of the molecule were prepared from simple esters and lactones by α-formylation followed by coupling with a bromofuranone. The α-formyl derivative of 2-coumaranone was prepared in good yield via the corresponding α-ethorymethylene compound. Evaluation of the biological activity of the new analogues lacking ring B and/or C revealed that the ABC part of the GR24 molecule is not essential for germination stimulation of Striga and Orobanche seeds []

Thermal Intramolecular cyclisation of enethiolisable (allylsulfanyl)sulfines affords 2-alkylidene-1, 3-dithiolane 1-oxides in good yields. The formation of these compounds is explained by an initial tautomerisation of the sulfine to vinylsulfenic acid, followed by an Intramolecular addition of the sulfenic acid to the allylic double bond. Also, sulfines having an S-(prop-2-ynyl) substituent have been investigated and they similarly give 2-alkylidene-5-methylene-1, 3-dithiolane 1-oxides. The results obtained by using thionyl chloride to promote the reaction turned out to be highly dependent upon the structure of the starting sulfine.