Photoinduced Decarboxylative Radical Coupling Reaction of Multiply Oxygenated Structures by Catalysis of Pt-Doped TiO₂

A new reaction system was devised for decarboxylative radical coupling reactions by heterogeneous semiconductor photoredox catalysis. When an α-alkoxy carboxylic acid and Pt-doped TiO₂ in EtOAc were irradiated with a violet light-emitting diode at room temperature, the photogenerated electron hole of TiO₂ oxidatively induced the ejection of CO₂ via the formation of a carboxyl radical to produce the corresponding α-alkoxy radical. C(sp³)-C(sp³) bond formation between the radicals led to dimers with reductive conversion of protons to H₂ by the photogenerated electron. Alternatively, in the presence of an electron-deficient olefin, an intermolecular radical addition reaction occurred, resulting in the formation of a 1,4-adduct via single-electron reduction and subsequent protonation. These operationally simple and mild transformations are amenable to the one-step assembly of densely oxygenated linear and branched carbon chains.