Iodine-zinc exchange reactions

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. 

Numerous modifications of the direct zinc insertion procedure can be found in the hterature. For example, simple diaUcylzincs can be used as reagents instead of metallic Zn, bnt in this case the reaction is accelerated by catalytic qnantities of zinc salts or transition metal see Transition Metals) salts. Whereas the Cu -catalyzed iodine-zinc exchange reaction provides diorganozincs, the Pd, Mn and nF catalyzed iodine- or bromine-zinc exchange leads to organozinc halides. 

Finally some transition-metal (Ni, Mn)-catalyzed iodine- or bromide-zinc exchange reactions using Et2Zn constitute a convenient approach to organozinc halides under mild reaction conditions [32,33] (Scheme 9-8). 

Recently, Knochel and co-workers [51] have reported that primary organic iodides undergo an iodine-zinc exchange reaction when treated with an excess of Et2Zn (5 equiv, neat, 50-55 °C, 10-14 h) and that several functional groups can be present in the organic iodides. In order to obtain further insight into the carbocyclization of dialkylzinc instead of... 

Knochel et al. comprehensively studied the preparation of functionahzed or-ganozinc species [32] and their application for an enantioselective alkylation of various aldehydes. An iodine-zinc exchange reaction in the presence of a cata-... 

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