Organozincs carbanion reactions

The Reformatsky reaction is a classical reaction in which metallic zinc, an a-haloester, and a carbonyl compound react to give a (i-hydroxyester.162 The zinc and a-haloester react to form an organozinc reagent. Because the carboxylate group can stabilize the carbanionic center, the product is essentially the zinc enolate of the dehalogenated ester.163 The enolate effects nucleophilic attack on the carbonyl group. 

It is the carbanion character of the organozinc compound that allows this reaction to proceed. The formation and reaction of the organozinc compound is similar to that of a Grignard reagent. Zinc is used in place of magnesium because organozinc compounds do not react with the ester function, but only with the aldehyde or ketone. Hydrolysis of the ester yields the corresponding acid. 

Organozinc compounds in which the ester group is farther removed from the carbanion center can also be prepared. This would not be possible for the more reactive lithium or magnesium reagents. The y-, and 5-esters can be made by reaction of the corresponding iodo esters with zinc-copper couple ... 

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