Transmetalation of Functionalized Organolithium and Organomagnesium Reagents

Many functional groups are incompatible with organolithium reagents. Execution of transmetalations at very low temperatures, however, enables functionalized 

CuCN 2LiCl. Tbis can then be selectively allylated with allyl bromide to provide the dibromoimidazole 36, which can now be magnesiated by treatment with a further equivalent of iPrMgBr, providing the ester-substituted imidazole 37 in 55% yield after carboxylation with ethyl cyanoformate [25]. 

Direct transmetalation of organoboranes to organocopper reagents is not a general reaction. Because of their similar bond energies and electronegativitieSj this transmetalation is limited to the preparation of alkenylcopper and unfunctionalized 

In the presence of a polar cosolvent such as hexamethylphosphoric triamide (HMPA)j it is possible to generate the fluorine-substituted copper compound 57, 

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