Direct C-2 Carboxylation of 3-Substituted Indoles Using a Combined Brønsted Base Consisting of LiO-tBu/CsF/18-crown-6

Abstract

Herein, we report that a combination of LiO-tBu, CsF, and 18-crown-6 can be used to carry out the carboxylation of indole derivatives at the C-2 position under an ambient CO2 atmosphere. Substrates bearing an electrophilic substituent (i.e., cyano, formyl, benzoyl, phenylsulfonyl, phenylsulfinyl, and chloride) at the C-3 position are smoothly converted into their corresponding carboxylated products with high functional group compatibility.