Recent advances in the photocatalytic synthesis of aldehydes

The synthesis of aldehyde compounds under mild conditions enabled by visible light-induced organic reactions is highly attractive in modern chemistry. Reagents including glyoxylic acid (or its derivatives), vinylene carbonate, methylamines, 1,3-dioxolane, and α-chloro N-methoxyphthalimide (PhthOCH₂Cl), are found to be sources of the aldehyde group in photocatalytic reactions. This review summarizes the recently developed photocatalytic strategies for the installation of the formyl group into various scaffolds, mainly through the key steps of photocatalytic decarboxylation, oxidation coupling with methylamines/hydrolysis, hydrogen atom transfer of 1,3-dioxolane, and direct generation of formyl radicals.