Catalysis

Benzonitrile

Photochemistry

Hydroperoxyl

Protonation

Electron acceptor

Molecule

Electron transfer

Substrate (aquarium)

Geology

Oceanography

Medicinal chemistry

Combinatorial chemistry

Organic chemistry

Carbanion

Radical

Chemistry

Carboxylation

Hydrogen bond

Journal of the American Chemical Society

The carboxylation of sp3-hybridized C-H bonds with CO2 is a challenging transformation. Herein, we report a visible-light-mediated carboxylation of benzylic C-H bonds with CO2 into 2-arylpropionic acids under metal-free conditions. Photo-oxidized triisopropylsilanethiol was used as the hydrogen atom transfer catalyst to afford a benzylic radical that accepts an electron from the reduced form of 2,3,4,6-tetra(9H-carbazol-9-yl)-5-(1-phenylethyl)benzonitrile generated in situ. The resulting benzylic carbanion reacts with CO2 to generate the corresponding carboxylic acid after protonation. The reaction proceeded without the addition of any sacrificial electron donor, electron acceptor or stoichiometric additives. Moderate to good yields of the desired products were obtained in a broad substrate scope. Several drugs were successfully synthesized using the novel strategy.

Photocarboxylation of Benzylic C–H Bonds