Organo-zinc reagents

The zinc organo-lialide is prepared for use by heating together the zinc-copper couple, the alkyl or aiyl halide, ethyl acetate, and toluene for about an hour, the reaction being started if necessary with a ciystal of iodine. All the reagents must be well dried, and the colomdess viscous liquid which results is ntilised by adding to it the acid chloride dissolved in toluene, and when the required amount has been added the intermediate zinc complex is decomposed by the addition of dilute sulphuric acid.1... 

Recently an example of a virtually complete diastereofacial selectivity in the 5n allylation of organo-copper/zinc reagents was reported. The best results were achieved with a new zinc cuprate reagent, the structure of which has not yet been elucidated (equation 33). This reagent was developed as a catalytic system for zinc alkyl reagents. 

As recent examples of copper-catalyzed asymmetric conjugate addition of organo-zinc reagents (a) Mizutani, H. ... 

See Reformatskv Reaction for further comments on the organo-zinc reagent. 

For the Knochel reaction an added Lewis acid is needed to enhance the 1,4-addition otherwise 1,2-addition would take place. A major advantage of the Knochel reagent is that other functional groups (ester, carbonyl, nitrile, Cl, sulfoxide and terminal alkyne) are possible with the organo-zinc starting material. 

Support-bound transition metal complexes have mainly been prepared as insoluble catalysts. Table 4.1 lists representative examples of such polymer-bound complexes. Polystyrene-bound molybdenum carbonyl complexes have been prepared for the study of ligand substitution reactions and oxidative eliminations [51], Moreover, well-defined molybdenum, rhodium, and iridium phosphine complexes have been prepared on copolymers of PEG and silica [52]. Several reviews have covered the preparation and application of support-bound reagents, including transition metal complexes [53-59]. Examples of the preparation and uses of organomercury and organo-zinc compounds are discussed in Section 4.1. 

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