Synthesis and Chemistry of 2,2,5,5-Tetramethylthiolane-3,4-dione. A Route to Bicyclopentyl-1-sulfonium Intermediates

Article abstract of DOI:10.1021/jo00144a008

The reaction of sodium sulfide with 2,5-dibromo-2,5-dimethylhexane-3,4-dione affords in good yield 2,2,5,5-tetramethylthiolane-3,4-dione (3a).This material has been converted to a variety of derivatives, including 2,2,5,5-tetramethyl-3-diazothiolane-4-one (3b) and the corresponding sulfone derivative.Compound 3b on treatment with electrophiles undergoes rapid substitution by the electrophile at the diazo carbon.The reaction of 3b with bromine was shown, however, to follow an indirect course involving the formation of a bicyclo<2.1.0>pentyl-1-sulfonium ion as probable intermediate; this is opened reversibly by attack of bromide at sulfur at lower temperature, whereas irreversible attack at carbon adjacent to carbonyl occurs at higher temperatures.Evidence for an ylidic variant of the 1-thiabicyclo<2.1.0>pentyl structure was obtained from the thermal decomposition of 3b.No trace of a Wolff rearrangement product was obtained.In contrast, the sulfone 18, derived from 3b by oxidation, on thermolysis afforded 3,3-dimethyl-4-(2-propenyl)oxathiolan-5-one 2-oxide (47).This product was shown, by means of trapping experiments, to arise from the ketene derived by normal Wolff rearrangement of 18 without participation of sulfur.Various other transformations, including 1,3-dipolar cycloadditions, of 3b and other derivatives, were investigated.