Subsequently (since 1992), asymmetric version of the reaction has been explored with excellent enantioselectivity (Scheme 9).
Scheme 9
Examples
3.2. 3 Transmetallation
Organozinc reagents proceed transmetallation thereby making them suitable candidates to be used in conjunction with transition metal salts. For example, RZnI reacts with CuCN·LiCl in THF to form new copper-zinc reagents that are generally formulated as RCu(CN)ZnI. The reactivity of this reagent is summarized in Scheme 10.
Scheme 10
Organozinc reagents when treated with CoBr2 generate organocobalt reagents that are stable for several hours at low temperature. Carbonylation is now possible by simply bubbling CO through such a solution (Scheme 11).
Scheme 11
The coupling allyl halide with organozinc reagents can be accomplished using cobalt(II) bromide at negative temperature (Scheme 12). The reaction occurs in a SN2 fashion thereby leading to a complete retention of double bond geometry.
Scheme 12
The reaction between organozinc reagent and an organic halide in the presence of Pd(0) or Ni(0) species is known as Negishi cross-coupling reaction which is one of the most widely used cross-coupling reactions for carbon-carbon bond formation (Scheme 11).
Scheme 11