Boron-zinc exchange reaction

Remarkably, by utilizing /-Pr2Zn for the boron-zinc exchange reaction, configurational well defined secondary dialkylzinc reagents, like 34, have been prepared for the first time (Scheme l.ll).37... 

Besides the iodine-zinc exchange reaction, the boron-zinc exchange reaction proves to be an excellent method for preparing a broad range of polyfunctional diorganozincs (Scheme 5.8). The exchange reaction for primary diethylalkyl boranes proceeds at room temperature and is complete within a few minutes. 

An example for the use of the boron-zinc exchange reaction for copper-mediated SN2 -substitutions of allylic electrophiles is the hydroboration of nitroolefin 130 with diethylborane, followed by successive transmetallation of the borane 131 with diethylzinc and CuCN-2LiCl, and final trapping with allyl bromide to give the product 133 with 83% yield over four steps (Scheme 34).34,34a This transformation again demonstrates the tolerance of the method towards functional groups and acidic hydrogen atoms. 

The boron-zinc exchange reaction as a source of polyfunctional... 

Pd(0)-catalyzed reactions also occur with retention of configuration. Thus, the hydroboration of 3-methylindene 10, followed by a boron-zinc exchange reaction with /-PraZn, gives the secondary dialkylzinc reagent 11 which undergoes a Pd(0)-catalyzed reaction with alkenyl iodides, such as 12, providing only the trans-indene 13 (Scheme 5) (10). 

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