Visible-light-induced decarboxylative cyclization.

The application of visible light as an energy source provides a new avenue in organic transformation due to its mildness, efficiency and selectivity. In fact, recent years have witnessed remarkable advances in photoinduced decarboxylative coupling reactions involving carboxylic acids and their derivatives. Under appropriate photoredox conditions they undergo single electron transfer (SET), resulting in reactive radicals which can assemble with suitable reaction partners. Many types of carboxylic acid derivatives, such as amino acids, N-hydroxy phthalimide (NHPI) esters, α-keto acids, aliphatic/aromatic carboxylic acids, and [bis(difluoroacetoxy)iodo]benzene, can couple with a wide variety of substrates to build structurally complex molecules. The present review summarizes the last five years of progress (2020-2024) in the decarboxylative cyclization of carboxylic acids for constructing carbo-/heterocycles under visible-light irradiation. Annulation could be attained via organophotocatalysis (4CzIPN, g-C3N4, Eosin Y, methylene blue, etc.), metallaphotocatalysis or photocatalyst-free approaches. With an emphasis on the mechanistic rationales and scope of the reactions, this review focuses on recent trends in this emerging area.