Vinyllithium reagents

Vinyllithium [917-57-7] can be formed direcdy from vinyl chloride by means of a lithium [7439-93-2] dispersion containing 2 wt % sodium [7440-23-5] at 0—10°C. This compound is a reactive intermediate for the formation of vinyl alcohols from aldehydes, vinyl ketones from organic acids, vinyl sulfides from disulfides, and monosubstituted alkenes from organic halides. It can also be converted to vinylcopper [37616-22-1] or divinylcopper lithium [22903-99-7], which can then be used to introduce a vinyl group stereoselectively into a variety of a, P-unsaturated systems (26), or simply add a vinyl group to other a, P-unsaturated compounds to give y, 5-unsaturated compounds. Vinyllithium reagents can also be converted to secondary alcohols with trialkylb o r ane s. 

Vinyl fluorinated zinc reagents can be prepared by two different methods (1) capture of the corresponding vinyllithium reagent at low temperatures with a zinc salt and (2) direct insertion of zinc into a carbon-halogen bond. 

C F[3CF=CFHgCgH5 (30%) [16. Vinyllithium reagents behave similarly [I81 (equation 128). 

It is unlikely that a (8-chelate analogous to 2 is responsible for the very high syn diastereoselectivity which is observed with the chiral vinyllithium reagent (7 )-3 upon addition to (/t)-3-(benzyl oxy)butanal (Table 13)11 °. 

Ketone p-toluenesulfonylhydrazones are converted to alkenes on treatment with strong bases such as an alkyllithium or lithium dialkylamide.286 Known as the Shapiro reaction,2 7 this proceeds through the anion of a vinyldiimide, which decomposes to a vinyllithium reagent. Treatment of this intermediate with a proton source gives the alkene. 

A variation of this strategy involves conjugate addition of the reagent formed from a 1 1 mixture of dimethylzinc and a vinyllithium reagent. The presence of dimethylzinc suppresses... 

B. Method (2) In Situ Capture of Vinyllithium Reagents at Ambient... 

The checkers used a 61-cm, 16-gauge cannula with a single loop ca. 6 cm in diameter Immersed in an isopropyl alcohol-dry ice bath. The submitters report that lower yields were obtained when the vinyllithium reagent was a llowed to warm above -78°C briefly during the transfer. 

Dienes and trienes.2 Alkyl- or vinyllithium reagents react with 1 to form a 1,2-adduct (a) that rearranges to a (2Z,4E)-5-substituted pentadienal (2) in 50-65% yield. The aldehyde can be used for a Wittig reaction or allowed to react with... 

Chamberlin and coworkers38 showed that vinyllithium reagents derived from ketone (2,4,6-triiso-propylphenyl)sulfonylhydrazones undergo intramolecular carbolithiadon reactions with high dia-stereoselectivity (Scheme 13). 

The synthesis of 3 was initiated by reaction of wBuLi with the protected cyclopentenone 2 generating the corresponding vinyllithium reagent by halogen-metal exchange. Subsequent condensation with (S)-(-)-menthyl para-toluenesulfinate (13) provides the enantiodefined sulfoxide substituent in 3.5 Since thermal equilibration of chiral sulfoxides at room temperature is slow, the large sulfur atom is a preferred reaction site in synthetic intermediates to introduce chirality into carbon compounds. 

Generation and functionalization of a fluorovinylzinc reagent prepared by capture of a vinyllithium reagent preparation of 1,1-difluoro-2-trifluoromethylpenta-1,4-diene13... 

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