Carboxylic Acid Salts as Dual-Function Reagents for Carboxylation and Carbon Isotope Labeling.

The potassium salts of carboxylic acids are developed as efficient carboxylating agents through CO 2 exchange. We describe these carboxylates as dual-function reagents because they function as a combined source of CO 2 and base/metalating agent. By using the salt of a commercially available carboxylic acid, this protocol overcomes difficulties when using CO 2 gas or organometallic reagents, such as pressurized containers or strictly inert conditions. The reaction proceeds under mild conditions, does not require transition metals or other additives, and shows broad substrate scope. Through the preparation of several biologically important molecules, we show how this strategy provides an opportunity for isotope labeling with low equivalents of labeled CO 2 .