Halides, vinyl from organometallic compounds

One requirement is diat the pKa of die new organometallic compound is lower than die pKa of die starting organometallic. This in essence means that the equilibrium is driven to products by die formation of a more stable anion. This metiiod is commonly used to make vinyl lithiums from vinyl halides and alkyl lithiums and aryl lithiums from aryl halides and alkyl litiiiums because the electron pair in an sp2 orbital of a vinyl or aryl litiiium compound is more stable than the electron pah in an sp3 orbital of an alkyl lithium. 

These problems may be avoided by making an organometallic compound [often of Cu(I) or Mg(II)] from the halide intended to become the palladium a-complex and to use another vinyl halide as the electrophile. Palladium prefers to take out a halide rather than a hydrogen atom in the P-elimination step and all three problems disappear. In the synthesis of this T, Z-dicnc 134, we prefer to use a Pd a-complex for the Z-alkene part 136 and a vinyl iodide 135 for the E-alkene. 

Organosodium compounds are prepared from sodium and other organometallic compounds or active methylene compounds by reaction with organic halides, cleavage of ethers, or addition to unsaturated compounds. Some aromatic vinyl compounds and allyhc compounds also give sodium derivatives. 

Oxidative addition of aryl (or vinyl) halide to Pd(0) precursor forms the monoarylpalladium complex that is the common intermediate in the catalytic cross-coupling reactions of haloarene with organometallic compounds of main group elements such as Mg, Si, and Sn. Alkynylcopper, formed from alkyne, Cu(I) salt and base in the reaction mixture, transfers the ligand to the above Pd complex, giving an intermediate complex with aryl (or vinyl) and alkynyl ligands bonded to Pd. Reductive elimination of arylacetylene (or enyne) occurs... 

As described above, the initial [Pd]—R complex can be formed by the transfer of R from another organometallic RM. Compounds of mercury, boron or tin have often been used. Alternatively an aryl, heteroaromatic or vinyl halide is added to PdL, generated in situ from PdL or by reduction of L PdX. In the second method a base such as a tertiary amine is also required to react with the hydrogen halide which is produced. 

Our initial strategy was to utilize F-vinyl halides as precursors. Many of these compounds are re ily available or easily prepared. Also, we anticipated that the formation of the organometallic reagent from the vinyl hdide would occur stereospecifically, thus permitting preparation of the appropriate E- or Z-organometallic by proper choice of the E- orZ-vinyl halide. 

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