Visible-Light Photocatalytic Nucleophilic Addition of 4-Pyridylphosphonium Salts to CO2 and Carbonyl Compounds

A visible-light photocatalytic nucleophilic addition of 4-pyridylphosphonium salts to CO₂ and carbonyl compounds is reported. The reaction has mild reaction conditions, good functional group tolerance, and a wide range of substrates. Mechanistic studies show that the reaction may occur through the pyridylphosphonium salt radical anion, pyridyl radical, and pyridyl anion intermediates. By combination with C4-H phosphination, this method can be applied to the late-stage C-H functionalization of drugs containing a pyridine unit.