Carbon dioxide: A reagent for the protection of nucleophilic centres and the simultaneous activation of alternative locations to electrophilic attack.

Indole was converted into several 2-substituted derivatives by using carbon dioxide both for N-protection and to give an intermediate carbanion stabilizing group. t-Butyllithium was used as a lithiating agent at the 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.