Vinyllithium reagents involving

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... 

The conditions originally employed for the Shapiro reaction involved treatment of the sulfonylhydrazone derivative with an alkyllithium reagent in hexane or ether solvent. Although these conditions are quite effective for the conversion of sulfonylhydrazones to alkenes (e.g., 1—>2), efforts to capture the intermediate vinyllithium reagent with electrophiles other than H+ are often met with limited success due to competing deprotonation of the solvent or the sulfonyl aryl group by the basic vinyllithium species. For example, treatment of 15a with >2 equiv of n-BuLi in hexane followed by quenching with D2O provided 16 in quantitative yield but with only -10% deuterium incorporation. A solution to this problem was developed independently by Shapiro and Bond that employs TMEDA (tetramethylethylenediamine) as an additive for Shapiro reactions.7,10 As shown below, use of TMEDA (4.0 equiv) as a cosolvent led to the conversion of 15b to 16 in quantitative yield with 95% deuterium incorporation. 

In both cases, sulfur stabilized the lithium derivative and reaction with alkyl halides proceeded in a manner analogous to other vinyllithium reagents. Hydrolysis required mercuric salts or another Lewis acid to give the ketone, as in the preparation of Ph2CHCOMe from 367. Another preparation involves direct treatment of an... 

The first method involves generation of an unstable vinyllithium denvative at low temperatures from the corresponding vinyl halide or 1-hydroalkene Addition of zinc chloride and warming to room temperature gives the stable vinyl zinc reagent [100, lOI, 102, 103] (equations 69-72)... 

The first method involves the generation of the vinyllithium at low temperature from the corresponding fluorinated vinyl halide or hydroalkene as described in Section 2.1.1.3.2.1. Addition of zinc halides to the lithium reagent solution gives the stable vinylzinc halides in excellent yields. 

The reactions of sulfonium salts with organometallic reagents probably involve five-coordinate sulfur species. For example, dephenylation of triphenyl-sulfonium tetrafluoroborate (37) with vinyllithium and the stereospecific... 

Preparative Methods attempts to produce synthetically useful quantities of ( )-2-(trimethylsilyl)vinyllithium (1) by reaction of lithium metal with (2-bromovinyl)trimethylsilane (2) failed because of concomitant metalation-elimination processes involving (1) and ) However, the transmetalation process between (2) and excess f-butyllithium has been effectively used to provide (1) (eq 1). An alternative route to (1) employs the transmetalation of a l-(trimethylsilyl)-2-stannylethylene with organolithium reagents (eqs 2 and 3). ... 

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