Heterocycles lateral lithiation

Electron-rich heterocycles, snch as pyrrole and furan, bear more resemblance to car-bocyclic rings their side chains are mnch less acidic, and undergo lateral lithiation mnch less readily. Without a second directing group, methyl groups only at the 2-position of fnran, pyrrole or thiophene may be deprotonated. 

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). 

The —CONHNR2 group of aromatic and heterocyclic 2,2-dialkyl hydrazides is a powerful director of ortho and lateral lithiation. Lithiation at C(7) of l-(2,2-diethylbutenoyl)indoles is directed kinetically by a complex-induced proximity effect of the nitrogen substituent which can be removed readily. ... 

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