Carboxylates lateral lithiation

Methylbenzoic acid 513 can be laterally lithiated with two equivalents of lithium amide base (LDA" or L1TMP °) or alkyllithium provided the temperature is kept low to avoid addition to the carbonyl group (Scheme 201). It is usually preferable to carry out the lithiation using aUcyllithiums", since with lithium amides the subsequent reaction of 514 with electrophiles is disrupted by the presence of the amine by-product (diisopropylamine, for example) . The dilithio species 514 is stable in THF even at room temperature, and (as with the amide 483) since LDA will also dilithiate 515 stabilization presumably comes principally from conjugation with the carboxylate. 

The reduced electrophUicity of indole-3-carboxylic esters (they are vinylogous carbamates) means that they are much more versatile directors of lateral lithiation than the comparable benzoates, as illustrated by the synthesis of 564 (Scheme 221... 

Dimethylfurazan also undergoes lateral lithiation with butyllithium and affords (methyl-furazanyl)acetic acid after carboxylation. The scope this process presents for achieving transformations involving pendant groups without disruption of the heterocycle is illustrated by the synthesis (Scheme 15) of methylvinylfurazan (81JHC1247). 

Knight explored the C2-lithiation of indole-3-carboxylic acids [326, 327]. Similar to the reaction with alcohol 100, two equivalents of LDA were used to generate dianion intermediates which upon quenching with electrophiles gave 2-(substituted)indole-3-carboxylic acids. This strategy was later used by Fisher... 

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