Coumarin-3-carboxylic acid: C3/C4-functionalizations and cyclization reactions

Due to the presence of a carboxyl group, coumarin-3-carboxylic acid can easily participate in C3-, and C4-functionalization, as well as cyclization reactions. The carboxyl moiety as a directing group enhances the reactivity of coumarins as dienophiles, which facilitates the participation of these scaffolds in the synthesis of various heterocycles. Hence, this review highlights the reports since 2010 on the contribution of coumarin-3-carboxylic acids in decarboxylative and cyclization reactions and discusses interesting reaction mechanisms.

Coumarins are privileged O-heterocycles and appear in biologically active natural and medicinal products. The presence of carboxyl as a directing group allowed coumarin-3-carboxylic acid to participate in C3-, or C4-functionalization, and annulations. This compound has attracted extensive attention from chemists in the field of cross-coupling methodologies to provide functionalized structures.