Visible-Light Photocatalytic Nucleophilic Additionof 4‑Pyridylphosphonium Salts to CO₂ and CarbonylCompounds

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.