Lithium vinyllithium

C. Cyclization Reaction of Acetylenic Allenyl Lithiums, Vinyllithiums and... 

Related syntheses using a variety of oiganolithium compounds have also been developed. Alkyl-lithiums, vinyllithiums or phenyllithiums in the presence of BF3-OEt2 give the oxirane and oxetane opening products in high yields (equation 39). ° Enolate-type nucleophiles can also be employed for this purpose (Scheme 18)." " ... 

Anionic polymerization of vinyl monomers can be effected with a variety of organometaUic compounds alkyllithium compounds are the most useful class (1,33—35). A variety of simple alkyllithium compounds are available commercially. Most simple alkyllithium compounds are soluble in hydrocarbon solvents such as hexane and cyclohexane and they can be prepared by reaction of the corresponding alkyl chlorides with lithium metal. Methyllithium [917-54-4] and phenyllithium [591-51-5] are available in diethyl ether and cyclohexane—ether solutions, respectively, because they are not soluble in hydrocarbon solvents vinyllithium [917-57-7] and allyllithium [3052-45-7] are also insoluble in hydrocarbon solutions and can only be prepared in ether solutions (38,39). Hydrocarbon-soluble alkyllithium initiators are used directiy to initiate polymerization of styrene and diene monomers quantitatively one unique aspect of hthium-based initiators in hydrocarbon solution is that elastomeric polydienes with high 1,4-microstmcture are obtained (1,24,33—37). Certain alkyllithium compounds can be purified by recrystallization (ethyllithium), sublimation (ethyllithium, /-butyUithium [594-19-4] isopropyllithium [2417-93-8] or distillation (j -butyUithium) (40,41). Unfortunately, / -butyUithium is noncrystaUine and too high boiling to be purified by distiUation (38). Since methyllithium and phenyllithium are crystalline soUds which are insoluble in hydrocarbon solution, they can be precipitated into these solutions and then redissolved in appropriate polar solvents (42,43). OrganometaUic compounds of other alkaU metals are insoluble in hydrocarbon solution and possess negligible vapor pressures as expected for salt-like compounds. 

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. 

Removal of the carbonate ring from 7 (Scheme 1) and further functional group manipulations lead to allylic alcohol 8 which can be dissected, as shown, via a retro-Shapiro reaction to give vinyl-lithium 9 and aldehyde 10 as precursors. Vinyllithium 9 can be derived from sulfonyl hydrazone 11, which in turn can be traced back to unsaturated compounds 13 and 14 via a retro-Diels-Alder reaction. In keeping with the Diels-Alder theme, the cyclohexene aldehyde 10 can be traced to compounds 16 and 17 via sequential retrosynthetic manipulations which defined compounds 12 and 15 as possible key intermediates. In both Diels-Alder reactions, the regiochemical outcome is important, and special considerations had to be taken into account for the desired outcome to. prevail. These and other regio- and stereochemical issues will be discussed in more detail in the following section. 

This type of metallic exchange is used much less often than 12-32 and 12-33. It is an equilibrium reaction and is useful only if the equilibrium lies in the desired direction. Usually the goal is to prepare a lithium compound that is not prepared easily in other ways, for example, a vinylic or an allylic lithium, most commonly from an organotin substrate. Examples are the preparation of vinyllithium from phenyl-lithium and tetravinyltin and the formation of a-dialkylamino organolithium compounds from the corresponding organotin compounds ... 

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. 

Triphenyl- [1] and trimethylvinylsilane [2] as well as l,l-bis(trimethylsilyl)ethylene [3] are known to react with lithium metal in THF yielding 1,4-dilithiobutane derivatives by a dimerizing Schlenk addition. Interestingly, by using hexane as the solvent trimethylvinylsilane 1 does not yield the dimer product 2 but a 1 1 -mixture of the corresponding vinyllithium compound 3 and the lithioalkyne 4... 

Starting with l,l-bis(trimethylsilyl)ethylene (5) in hexane or diethyl ether as the solvent we obtained another dimeric product, a monolithiumorganic compound 8 which was shown not to be formed by lithium hydride elimination from the 1,4-dilithiobutane derivative 6, the only product in THF as the solvent. Obviously the vinyllithium derivative 7, primarily formed in the same manner as vinyllithium from ethylene [4], in contrast to vinyllithium [4] does not add further lithium atoms but adds itself to the starting material 5 yielding 8 ... 

A fascinating reaction takes place starting with 9c (R = PhCMe2) and lithium powder in THF as the solvent. From the primarily formed 1,2-dilithioethane derivative 10c cumyllithium 12 is split off and the 2,2-bis(trimethylsilyl)vinyllithium 11 quantitatively dimerizes to yield the deep red dili-thiobutene derivative 13 ... 

Vinyllithium cyclizations. The vinyl lithiums formed from trisylhydrazones (9, 486) can participate in intramolecular cyclizations. This anionic cyclization is presently limited to formation of five-membered rings. It has the advantage of greater stereoselectivity than a corresponding radical cyclization. 

A tanden anh-vicinal difunctionalization of alkynes, involving the addition of a lithium organotellurolate to an activated alkyne, with subsequent trapping of the vinyllithium intermediate with electrophiles, was recently reported and named electrotelluration. ... 

Transmetallations of vinylic tellurides deserve particular attention. These tellurides (prepared by anti-addition of tellurols to acetylenes, see Section 3.16.1.2) exhibit the Z configuration and therefore generate (Z)-vinyUithiums. These results are in sharp contrast to the earlier tin-lithium exchange performed with vinylstannanes (characterized by the E configuration), giving (ii)-vinyllithiums. ... 

Lithium-tellurium exchange generation of vinyllithium (typical procedure). Method A. To a solution of butyl vinyl telluride (0.211 g, 1 mmol) in THF (4 mL) at -78°C under N2 is added dropwise a solution of n-BuLi (1.5 M in hexane, 0.67 mL, 1 mmol). After stirring for 40 min at -78°C, benzaldehyde (0.016 g, 1 mmol) is added. The mixture is allowed to react at room temperature for 30 min, diluted with EtOAc (40 mL) and washed with brine. 

The dilithiated vinyllithium compound 1,2-dilithioethylene (132) was synthesized by Maercker and coworkers, using the mercury-lithium exchange reaction . Bis(chloromercurio)ethylene (131) was reacted with four equivalents of f-butyllithium... 

The present synthesis of 4,6-dimethyl-l-hepten-4-ol is an example of the preparation and use of allyllithium, hitherto unknown as a pure reagent. The same general procedure may be used to prepare vinyllithium from ether solutions of any of the compounds (CH2=CH) Sn(CeH,5)4 ( = 1-4), and benzyl-lithium from any of the (CeH6CH2)nSn(C6H5)4 n(w = 1-4) compounds.10... 

SPIR0ANNELAT10N Lithium chloride-Hexamethylphosphoric triamide. N-Methyl-N-phenylaminoacetylene. (EE a(Trimethylsilyl)vinyllithium. 

Imines of acylsilanes are excellent precursors of SMA (See Section III.B.l.m). Insertion of an isonitrile into the C-Li bond of a lithium reagent, followed by the silylation of the resulting vinyllithium derivative affords such imines.160... 

Vinyllithium, LiHC=CH2, has a similar tetrameric structure in the crystalline state with a THF ligand attached to each lithium atom [Fig. 12.3.1(b)], In THF solution vinyllithium is tetrameric as well. The internuclear Li-H distances are in agreement with those calculated from the two-dimensional NMR 6Li, XH HOSEY spectra. 

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