Regiodivergent Ligand-Controlled Cobalt-Catalyzed Reductive Hydroxymethylation of Alkynes with Aqueous Formaldehyde.

Allylic alcohols are versatile and essential building blocks in synthetic chemistry, widely used for the preparation of complex molecules, pharmaceuticals, and materials. We report here a regiodivergent reductive hydroxymethylation of terminal alkynes with aqueous formaldehyde to prepare allylic alcohols enabled by visible light photoredox and cobalt dual catalysis. Using readily available, bulk, and cheap aqueous formaldehyde as a simple C1 source, this method allows for the selective production of both linear and branched allylic alcohols in one-step manner. The excellent regioselectivity of the reaction is effectively controlled by adjusting the electronic and steric properties of the ligands. Moreover, regioselective reductive hydroxymethylation of internal alkynes with aqueous formaldehyde has also been achieved by careful selection of ligands. Mechanistic studies reveal a pathway involving ligand-controlled regioselective oxidative cyclometallation of the alkyne and formaldehyde, followed by a protonolysis process, offering new insights into the catalyst design and reaction mechanism.