Carbon dioxide: A reagent for the protection of nucleophilic centres and the simultaneous activation of alternative locations to electrophilic attack. : Part I. A new synthetic method for the 2-substitution of 1-unsubstituted indoles.

Indole was converted into several 2-substituted derivatives by using carbon dioxide both for $\text{N}$-protection and to give an intermediate carbanion stabilizing group. $\text{t}$-Butyllithium was used as a lithiating agent at the $\text{alpha}$-carbon atom of the indole enamino group. The resulting 2-substituted indole-1-carboxylic acids underwent smooth thermal decarboxylation under mild conditions. Alternatively, with longer reaction times the protecting group is lost during the reaction.