Organometallics species Organozincs

More attractive copper-catalyzed (mediated) transformations of allenes into alkynes were reported by Caporusso and co-workers [27f, 73-75], Allenes 142 were converted into alkynes 143 by treatment with stoichiometric amounts of a cuprate species, as exemplified in Scheme 14.35. The problem of regioselective formation of either alkyne 143 or allene 144 was solved by the proper choice of the organometallic species. Preferential formation of alkynes 143 could be achieved employing cuprates such as R3Cu(CN)ZnCl-LiCl, which are prepared from organozinc compounds. On the other hand, reactions of organomagnesium derived cuprates (R3CuBr)Mg-LiBr mostly provided allenes 144 as major components. 

Due to the low reactivity of alkyl and arylorganozinc reagents towards alkenes and alkynes, it appears clear that the carbozincation chemistry for this class of reagents is intimately associated with transition metal catalysts. Some of the metal-catalyzed/promoted reactions do indeed produce organozinc reagents as the final organometallic species that can further react with an appropriate electrophile, whereas other processes lead to highly functionalized products by an entirely different pathway. 

Organozinc, organomagnesium or other organometallic species can be effective partners in palladium-catalysed coupling reactions. Metals other than palladium(O), such as nickel(0) or copper(I) (see Section 1.2.1), can alternatively be used to promote cross-coupling of unsaturated halides and organometallic species. ... 

Oxidative cross-coupling reactions may start from two organometallic species to yield a new C-C single bond (for the oxidative C-X formation, see 10.4). A prototypical example is stated in Scheme 5-143. In this procedure, palladium is first oxidized by the haloketone 2-chloro-2-phenylacetophenone, and the resulting palladium OPdCl complex then accepts both organozinc and organotin compounds in a double transmetalation to yield an oxidative cross-coupling. ... 

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