Dual Photoredox/Cobalt-Catalyzed Reductive Cyclization of Alkynals

Substituted cyclic alcohol is one of the pharmaceutically essential scaffolds. Here, we report photoredox/cobalt-catalyzed reductive cyclization of alkynals using H2O for the catalyst turnover. This method was applied to aliphatic and aromatic aldehydes for five-, six-, and seven-membered (heterocyclic) ring formation with various substitutions on alkyne units. This H2O-added protocol was further developed into a one-pot transformation from acetals through in situ generated aldehydes, which shortened the synthetic path of the reaction.