The generation and synthetic applications of episulfone α-anions

Abstract

Treatment of the episulfone, 8,8-dimethyl-2,3-epithio-6,10-dioxaspiro[4.5]decane S,S-dioxide 1, with lithium diisopropylamide to generate the corresponding α-sulfonyl anion, and anion trapping with trimethylsilyl chloride or trimethylstannyl chloride in situ, produced the corresponding monosilyl, disilyl, monostannyl and distannyl episulfones as relatively stable, fully characterised crystalline solids. The structure of the disilylated episulfone 3a was also confirmed by X-ray crystallography: this is the first reported X-ray structure of a tetrasubstituted episulfone and the long carbon–carbon episulfone bond length (1.686 Å) is particularly noteworthy. With similar procedures the monotriethylsilyl, monotributylstannyl, and the triethyl, trimethyl disilyl adducts were prepared in reasonable to good yields. On treatment with potassium tert-butoxide or thermolysis the functionalized episulfones lost sulfur dioxide to produce the corresponding vinyl-silanes and -stannanes. Attempts to use carbon electrophiles for α-sulfonyl anion trapping are also reported. The monobenzoylated adducts 9 and 10 were obtained by in situ trapping with benzoyl chloride. In addition, it was found that treatment of the disilylated episulfone 3a with caesium fluoride–benzaldehyde gave the monoalkylated adduct 11, albeit in low yield. Other reactions of the silylated/stannylated episulfones are also reported.