Photocatalyzed Insertion of CO2 into Benzylic C–H Bonds

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  • Published: 22 July 2019
  • Copyright: Wiley-VCH Verlag GmbH & Co. KGaA
  • Source / Publisher: Journal of the American Chemical Society/ACS Publications
  • Associated Societies: American Chemical Society (ACS), USA
thumbnail image: Photocatalyzed Insertion of CO<sub>2</sub> into Benzylic C–H Bonds

The greenhouse gas CO2 could be used as a sustainable chemical feedstock. It can, for example, be used to convert organic compounds into carboxylic acid derivatives. However, the direct carboxylation of C(sp3)–H bonds is still challenging.

Burkhard König, University of Regensburg, Germany, and colleagues have developed a visible-light-mediated carboxylation of benzylic C–H bonds with CO2 to give 2-arylpropionic acids (pictured). The team used 2,4,5,6-tetra(carbazol-9-yl)isophthalonitrile (4CzIPN) as a photosensitizer, triisopropylsilanethiol as a hydrogen atom transfer catalyst, and N,N-dimethylformamid (DMF) as the solvent. They converted a variety of compounds with benzylic C–H bonds into the corresponding carboxylic acids under visible light in moderate to excellent yields.

The proposed mechanism involves a single-electron oxidation of triisopropylsilanethiol, which produces a radical. This radical abstracts hydrogen from the substrate, giving a benzyl radical. The benzyl radical can then be reduced to give a carbanion, which reacts with CO2. The overall reaction is metal-free, atom-economic, and can, e.g., be used to synthesize commonly used drugs.



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