Organolithium reagents alkenyllithium

Alkenyllithium compounds can also be prepared by metallation of alkenes, particularly when alkenyl hydrogens are rendered acidic by an a-substituent (equation 22). Transmetallation of alkenyl stannanes with organolithium reagents gives alkenyllithium compounds with retention of alkene stereochemistry (equation 23). Tin-lithium transmetallation has been used to prepare 1,4-dilithio-l,3-butadiene. Monosubstituted alkenyllithium compounds RHC=CHLi, can also be prepared from the corresponding diorganotel-luride, RHC=CHTeBu, by reaction with butyllithium in... 

If the alkenyllithium 43 is used as organolithium compound with 39, siloxyallyllithium reagents 44 are formed ". As example, the isomerization of the silyl(allyl)alkoxides 44 gives the corresponding lithio-(Z)-silyl enol ethers 45 which react with various electrophiles to give 46 (equation 17) . ... 

This reaction proceeds in the forward direction when the new lithium reagent RLi formed is a weaker base (more stable carbanion) than the starting organolithium R Li. The method is best suited for exchanges between Csp3-Li (stronger base) and C pa-X to give alkenyllithiums, C pz-Li (weaker base). ... 

Addition of a number of alkyUithium and alkenyllithium reagents and phenyl-lithium to 558 was successful. However, efforts to introduce functionality at C(4) in 561 via organolithiums 562-566 was unsuccessful, despite considerable experimentation. The authors reported that FVP of 560 usually afforded better yields of 561 and cleaner material. Cyclization of 560 with TMSOTf was favored for higher molecular weight substrates. A limitation of the methodology concerned preparation of 558, which was not available by alkylation using LDA. 

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