(E)- and (Z)-1-(Phenylsulfonyl)-4-(trimethylsilyl)-2-butenes:  Synthetic Equivalents for the 1-(1,3-Butadienyl) Anion and the 1,1-(1,3-Butadienyl) Dianion

(E)- and (Z)-1-(phenylsulfonyl)-4-(trimethylsilyl)-2-butenes (7 and 8) are converted by n-BuLi to (E)- and (Z)-1-lithio-1-(phenylsulfonyl)-4-(trimethylsilyl)-2-butenes (15 and 16) with retention of initial stereochemistries. Reactions of 15 and 16 with electrophiles (protio and deuterio acids, primary, secondary, and benzyl halides, chloroformates, chlorothioformates, acid chlorides, epoxides, trialkylsilyl chlorides, and triethylgermanyl chloride) in THF or THF/HMPA give the corresponding (E)- and (Z)-1-(phenylsulfonyl)-1-substituted-4-(trimethylsilyl)-2-butenes (32) with stereochemical retention. That β,γ-unsaturated silyl sulfones 32 are formed instead of their α,β-unsaturated (conjugated) isomers are attributed to stabilizing multiple anionic and cationic hyperconjugation and to steric effects as in 29−31. Of importance in synthesis is that 32 are eliminated by TBAF at −20 to 0 °C, thermally, or by column chromatography to (E)- (100 to > 93%) rather than (Z)-1-substituted-1,3-butadienes (38). Further, 32 undergo conversions by n-BuLi and various alkylating agents to (unconjugated) 1-(phenylsulfonyl)-1,1-disubstituted-4-(trimethylsilyl)-2-butenes (46) with retention of stereochemistry. Eliminations of 46 by fluoride ion, acid catalysis, or heat yield 1,1-disubstituted-1,3-butadienes (53). Silyl sulfones 7 and 8 are thus synthetic equivalents for the (E)-1-(1,3-butadienyl) anion (44) and the 1,1-(1,3-butadienyl) dianion (57). Silyl sulfones 7 and 8 also undergo efficient stereospecific intramolecular conversions by n-BuLi and α,ω-dihalides to 1,1-cycloalka-1-(phenylsulfonyl)-4-(trimethysilyl)-2-butenes (62 and 71) that are eliminated by fluoride ion, heat, or adsorption chromatography to 1,1-cycloalka-1,3-butadienes (72).