Organolithium reagents, reaction with alkenes

The products obtained from the reaction of (chloromethyl)trimethylsilane with organolithium reagents depend very much on the structure of the lithium compound. While lithium 2,2,6,6-tetramethylpiperidide initiates an a-elimination as described above, the treatment with sec-butyllithium leads to the formation of chloro(trimethylsilyl)methyllithium (11). This reagent cyclopropanates an electron-deficient alkene through sequential Michael addition and intramolecular ring closure (MIRC reaction), for example, the formation of cyclopropane 12. 

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... 

G.ii. Intramolecular Addition to Alkenes and Alkynes. Organolithium reagents can react with alkenes or alkynes in an intramolecular reaction, although both are relatively inert to the analogous intermolecular reaction. Ward treated alkynyl bromide 263 with n-butyllithium and observed a 60% yield of... 

Reaeting nickelocene with organolithium reagents in the presence of alkenes or alkynes generates a number of unusual species. For instance, the reaction of nickelocene with LiPh in the presence of 1-decene in THF gave... 

Reactions with other aldehydes produce secondary alcohols. Although the presence of most other functional groups (OH, NH, carbonyl groups, and so on) must be avoided because they react with Grignard or organolithium reagents, ether and alkene groups can be present ... 

Taylor and Wei have also developed a versatile method for the synthesis of cyclopentanes employing readily available organolithium compounds as difunctional, conjunctive reagents. This strategy represents an anionic [3 + 2] approach to substituted cyclopentanes. The reactions of lithiated alkenes 149 with activated alkenes 150 afford cyclopentane derivatives 151 in reasonable yield and, in some cases, with excehent stereocontrol. The alkenes 150 must be added over extended times to minimize polymerization processes. The... 

The reaction of alkyllithium reagents with acyclic and cyclic tosylhydrazones can lead to mixtures of elimination (route A) and addition (route B) products (Scheme 22). The predominant formation of the less-substituted alkene product in the former reaction (Shapiro Reaction) is a result of the strong preference for deprotonation syn to the N-tosyl group. Nucleophilic addition to the carbon-nitrogen tosyl-hydrazone double bond competes effectively wiA a-deprotonation (and alkene formation) if abstraction of the a-hydrogens is slow and excess organolithium reagent is employed. Nucleophilic substitution is consistent with an Su2 addition of alkyllithium followed by electrophilic capture of the resultant carbanion. 

Evidence for a radical coupling mechanism (as opposed to a carbanionic carbonyl addition mechanism) in the intramolecular Smh-promoted Barbier reactions has come from studies on appropriately functionalized substrates in the 3-keto ester series. It is well known that heterosubstituents are rapidly eliminated when they are adjacent to a carbanionic center. Indeed, treatment of a 3-methoxy organic halide (suitably functionalized for cyclization ) with an organolithium reagent leads only to alkene (equation 48). No cyclized material can be detected. On the other hand, treatment of the same substrate with Sml2 provides cyclized product and a small amount of reduced alcohol, with none of the alkene detected by gas chromatographic analysis (equation 49). ... 

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