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Piperidinium tetrathiotungstate has been found to react with a number of 1,n-dihalo compounds to afford the corresponding cyclic disulfides in good yields, under mild reaction conditions. This new methodology has been used as a key step in the synthesis of (+/-)-lipoic acid (35) and asparagusic acid (37).

The diazirine 1, upon thermolysis or photolysis in either acetone or cyclohexanone, at different concentrations, yield the spiro epoxides 2 and 3, and 4 and 5, respectively (Scheme 1). Yield of 2 and 3 depended both on the temperature and the concentration, and correlated inversely with the yield of the major by-product, the enol-derived glycoside 6. Other by-product were the benzyloxglycal7 and the lactone azines 8. ZnCl2-Promoted methanolysis of 2 under mild condition yielded mixture of the uloside 9 and 10 (1.2:1); similarly, 4 yielded 11 and 12 (1.8:1; Scheme 2). More strongly acidic conditions converted 11 into 12, evidencing that ZnCl2-promoted methanolysis proceeds under kinetic control, which is rationalized. The diazirine 13, upon thermolysis of Photolysis in either acetone of cyclohexanone, yielded the α-D-configurated spiro epoxides 14 and 16, and the α-D-configurated dihydrooxazoles 15 and 17, respectively (Scheme 3), which are either formed by ring-opening of s-D-epoxides, by competitive interception of the initially formed, hypothetical addition products of the intermediate carbene to the ketones. The glycosylidene carbenes, derived from 1 or 13 are not very reactive towards ketones, yields are good only when sterically unhindered ketones are used in large excess.

In an unusually novel reaction, piperidinium tetrathiotungstate has been found to induce reductive dimerization of a variety of sulfonyl derivatives to the corresponding disulfides under very mild conditions

L'alkylation de tetrathiotungstate et de tetrathiomolybdatede piperidinium permet la synthese, en conditions douces, de disulfures organiques