| Abstract
| - (E)- and(Z)-1-(phenylsulfonyl)-4-(trimethylsilyl)-2-butenes(7 and 8) are converted by n-BuLito(E)- and(Z)-1-lithio-1-(phenylsulfonyl)-4-(trimethylsilyl)-2-butenes(15 and 16) with retention ofinitial stereochemistries. Reactions of 15 and16 with electrophiles (protio and deuterioacids,primary, secondary, and benzyl halides, chloroformates,chlorothioformates, acid chlorides, epoxides,trialkylsilyl chlorides, and triethylgermanyl chloride) in THF orTHF/HMPA give the corresponding(E)- and(Z)-1-(phenylsulfonyl)-1-substituted-4-(trimethylsilyl)-2-butenes(32) with stereochemicalretention. That β,γ-unsaturated silyl sulfones 32are formed instead of their α,β-unsaturated(conjugated) isomers are attributed to stabilizing multiple anionic andcationic hyperconjugationand to steric effects as in 29−31. Ofimportance in synthesis is that 32 are eliminated byTBAFat −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 andvariousalkylating agents to (unconjugated)1-(phenylsulfonyl)-1,1-disubstituted-4-(trimethylsilyl)-2-butenes(46) with retention of stereochemistry. Eliminations of46 by fluoride ion, acid catalysis, or heatyield 1,1-disubstituted-1,3-butadienes (53). Silylsulfones 7 and 8 are thus syntheticequivalentsfor the (E)-1-(1,3-butadienyl) anion (44) and the1,1-(1,3-butadienyl) dianion (57). Silyl sulfones7and 8 also undergo efficient stereospecific intramolecularconversions by n-BuLi and α,ω-dihalidesto 1,1-cycloalka-1-(phenylsulfonyl)-4-(trimethysilyl)-2-butenes(62 and 71) that are eliminated byfluoride ion, heat, or adsorption chromatography to1,1-cycloalka-1,3-butadienes (72).
|
