Pd/C-Catalyzed Hydrocarboxylation and Carbonylative Esterification of Indoles to Indole-3-carboxylic Acids and Esters.

An unprecedented and robust Pd/C catalytic platform has been introduced for regioselective hydrocarboxylation as well as carbonylative esterification of indoles with aliphatic alcohols employing oxalic acid as the CO precursor. The developed strategy efficiently enables the synthesis of diverse classes of indole-3-carboxylic acids and esters with excellent regioselectivity and good yields under mild reaction conditions. Notably, phosphine ligand-free conditions, utilization of economical and bench-stable oxalic acid as the C1 source, commercially accessible and reusable Pd/C as a catalyst, and gram scale applicability are the additional benefits of the established methodology.