Base-Mediated Carboxylation of Unprotected Indole Derivatives with Carbon Dioxide

A simple and straightforward method for the preparation of indole-3-carboxylic acids was discovered through the direct carboxylation of indoles with atmospheric pressure of carbon dioxide (CO2) under basic conditions. The key for the reaction was found to be the use of a large excess of LiO'Bu as a base to suppress the undesired decarboxylation side reaction.