Favorskii rearrangement carboxylic acid branching

This means that it can be used to build up heavily branched esters and carboxylic acids—the sort that are hard to make by alkylation because of the problems of hindered enolates and unreactive secondary alkyl halides. Heavily substituted acids, where CO2H is attached to a tertiary carbon atom, would be hard to make by any other method. And the Favorskii rearrangement is a key step in this synthesis of the powerful painkiller Pethidine. 

One of the most common early uses of the Favorskii rearrangement was for the preparation of highly branched carboxylic acids and esters. For instance, when 3-bromo-3-methyl-2-butanone is treated with sodium isopropoxide at room temperature, isopropyl trimethylacetate is generated in 64% yield. ... 

Favorskii rearrangement is the base-catalyzed transformation of a-haloketones into the corresponding carboxylic acid or carboxylic acid derivative. Alexey Favorskii described the rearrangement that has his name more than a century ago. Since then, this reaction has been used in a variety of different manners, particularly in the synthesis of highly branched systems. Herein, examples regarding the ring contraction will be discussed. 

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