Preparation of trans-β-trimethylsilylvinyllithium
Clayton, Frederick J.
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This investigation was concerned with the synthesis of stereochemically pure cis- and trans-β-trimethylsilylvinyllithium. Although synthesis of the cis isomer was never realized, the trans isomer was prepared in 99+% isomeric purity, as adjudged by derivatization. Various preparations of trans-β-trimethylsilylvinyllithium are described. The low temperature reaction of cis-(β-chlorovinyl)trimethylsilane with lithium metal produced cis-trans organolithium mixtures in low yield. Room temperature transmetalation of trans-(β-trimethy1- silylvinyl)tri-n-butyltin with n-butyllithium afforded pure trans-β-trimethylsilylvinyllithium in moderate yields (53% of chlorotrimethylsilane derivatized product), while at low temperature, pure trans-β-trimethylsilylvinyllithium was formed in high yield (81-90%) as evidenced by derivatization with 1,2-dibromoethane, carbon dioxide, chlorotrimethylsilane, and n-butyl bromide. Nearly as high yields were realized from the transmetalation of trans-(β-trimethylsilylvinyl)triphenyltin with phenyllithium, but here an equilibrium situation seemed to be encountered. Attempted syntheses of a cis-stannane precursor to transmetalation are also described.