Decarboxylative Functionalization of Carboxylic Acids with Easily Oxidizable, Unstable, and Difficult Substituents under Visible Light Irradiation

Decarboxylative functionalization of carboxylic acids via carboxyl radical generation is an important strategy in organic synthesis. Carboxylic acids, widely found in nature as amino acids, peptides, fatty acids, and sugar acids, have the high abundance, accessibility, and stability. Decarboxylation of simple carboxylic acids such as acetic acid and fluoroalkyl carboxylic acids leads to the formation of synthetically useful methyl and fluoroalkyl radicals. The high stability of the carboxyl group toward air and moisture as well as the high functional group tolerance of radical reactions enable the application of aliphatic carboxylic acid functionalities in late‐stage transformations during the synthesis of complicated organic molecules, such as natural products and pharmaceuticals. This review focuses on recent advancements in decarboxylative functionalization under visible light irradiation, highlighting carboxylic acids with easily oxidizable, unstable, and difficult substituents. In addition to visible‐light‐induced transformations, this review summarizes electrochemical and thermal reactions as complementary methods for decarboxylative transformations.