Vinyl lithium compounds

When the enamine is in conjugation with a carbonyl function, as in a-aminomethylene aldehydes (528,529), ketones (530), or esters (531), a Michael addition is found in vinylogous analogy to the reactions of amides. An application to syntheses in the vitamin A series employed a vinyl lithium compound (532). 

Vinylic copper reagents react with CICN to give vinyl cyanides, though BrCN and ICN give the vinylic halide instead." Vinylic cyanides have also been prepared by the reaction between vinylic lithium compounds and phenyl cyanate PhOCN." Alkyl cyanides (RCN) have been prepared, in varying yields, by treatment of sodium trialkylcyanoborates with NaCN and lead tetraacetate." Vinyl bromides reacted with KCN, in the presence of a nickel complex and zinc metal to give the vinyl nitrile. Vinyl triflates react with LiCN, in the presence of a palladium catalyst, to give the vinyl nitrile." ... 

Reaction betweeen vinylic lithium compounds and silyl peroxides... 

Generally, a-heteroatom-substituted alkyl and vinyl lithium compounds are generated in solution under inert conditions at appropriate low temperatures and allowed to react further without isolation. The acidity of monohalogen-substituted alkanes is usually not high enough to permit the generation of a-lithio-a-halogen alkanes by deprotonation. 

A similar type of substitution, which clearly shows the electrophilic character, occurs in vinylidene carbenoids. In an early example of this reaction, Kobrich and AnsarP observed that the aUcene 70 results when the fi-configurated vinyl lithium compound 68 is treated with an excess of butyllithium and the fithioafkene 69 formed thereby is protonated (equation 41). Obviously, the nucleophilic attack of the butyl residue on the carbenoid takes place with inversion of the configuration. 

Evidence for this mechanism is (1) two equivalents of RLi are required (2) the hydrogen in the product comes from the water and not from the adjacent carbon, as shown by deuterium labeling 209 and (3) the intermediates 31-33 have been trapped.210 This reaction, when performed in tetramethylenediamine, can be a synthetically useful method211 of generating vinylic lithium compounds (33), which can be trapped by various electrophiles such as D20 (to give deuterated alkenes), C02 (to give a, 3-unsaturated carboxylic acids—6-34), or DMF (to give a, 3-unsaturated aldehydes—0-105). 

Reaction betweeen vinylic lithium compounds and silyl peroxides 5-18 Michael-type reaction in the presence of MejSiCl... 

Normant, J.-F. Synthesis of selectively fluori-nated substrates via organometallic reagents derived from CF2=CFC1, CF2=CC12, CF2=CH2. J. Organomet. Chem. 1990, 400,19-34. Schmidt, R. R. Talbiersky, J. Russegger, P. Generation of functionally substituted vinyl-lithium compounds. Results and calculations. Tetrahedron Lett. 1979, 4273-4276. 

One example was also reported showing the formation of an (El-alkenyl sulfoxide in the reaction of a vinylic lithium compound on menthyl sulfinate (eq 4). ... 

In previous chapters the influence of the gegenion and the solvent on rearrangements of carbanions mostly concerned the rate of a certain reaction (and thus kinetic aspects), as, e.g., in the case of the cyclopropyl-allyl anion rearrangement (Sect. 2.1), the ally anion isomerization (Sect. 2.2), the cyclization of 5-hexenyl alkali metal compounds (Sect. 4) or the configurational isomerization of a-substituted vinyl-lithium compounds (Sect. 5). 

Just as anions of allyl derivatives can be homoenolate equivalents (chapter 13) so anions of vinyl derivatives can be acyl anion equivalents. Vinyl (or enol) ethers can be lithiated reasonably easily, especially when there is no possibility of forming an allyl derivative, as with the simplest compound 81. The most acidic proton is the one marked and the vinyl-lithium derivative 82 reacts with electrophiles to give the enol ether of the product17 84. However, tertiary butyl lithium is needed and compounds with y-CHs usually end up as the chelated allyl-lithium 85. These vinyl-lithium compounds add directly to conjugated systems but the cuprates will do conjugate addition.18... 

Whereas in the aromatic and hetero-aromatic series halogen-lithium exchange is a useful reaction, it is much less important for the generation of vinylic lithium compounds. The desired bromine-lithium exchange is often accompanied by dehydrohalogenation reactions [9], e.g. ... 

Vinyl-lithium Compounds. H. Neumann and D. Seebach, Chem. Ber., 1978, 111, 2785. CH2== CRLi from CH2=CRBr and two equivalents Bu Li. 

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