Since C—H bond is the basic unit of organic compounds, it’s considered to be a concise synthesis method to implement direct functionalization of C—H bond. As carboxylic acids are widely found in nature, carboxyl group can act as both directing group and leaving group to drive transition metal-catalyzed controllable transformation of ortho-C—H bond functionalization of carboxylic acid that not only avoids the extra introduction and removal of the directing group in the process of C—H bond activation, but also highlights the simplicity of C—H bond activation and green of decarboxylation with “one stone and two birds” strategy of the carboxyl group. Therefore, basing on the strategy of “two birds with one stone”, ortho-C—H bond functionalization of carboxylic acid using carboxyl as a traceless directing group can provide a new strategy and method for controllable and directional synthesis, which has considerable significance in synthetic chemistry. According to the types of coupling partners involved in the transformations, transition metal-catalyzed ortho-C—H bond activations of carboxylic acids with multiple-bond-containing reagents, arylating compounds and heteroatom-containing chemicals are reviewed respectively based on the strategy of “two birds with one stone”, and the relevant reaction mechanisms are discussed.

Key words: carboxylic acid, traceless directing group, C—H bond activation, decarboxylation, functionalization