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Redox-neutral Photocatalytic C-H Carboxylation of Arenes and Styrenes with CO2
preprintsubmitted on 16.06.2020, 05:55 and posted on 17.06.2020, 10:06 by Matthias Schmalzbauer, Thomas D. Svejstrup, Florian Fricke, Peter Brandt, Magnus J. Johansson, Giulia Bergonzini, Burkhard Koenig
Carbon dioxide (CO2) is an attractive one-carbon (C1) building block in terms of sustainability and abundance. However, its low reactivity limits applications in organic synthesis as typically high-energy reagents are required to drive transformations. Here, we present a redox-neutral C−H carboxylation of arenes and styrenes using a photocatalytic approach. Upon blue-light excitation, the anthrolate anion photocatalyst is able to reduce many aromatic compounds to their corresponding radical anions, which react with CO2 to afford carboxylic acids. High-throughput screening and computational analysis suggest that a correct balance between electron affinity and nucleophilicity of substrates is essential. This novel methodology enables the carboxylation of numerous aromatic compounds, including many that are not tolerated in classical carboxylation chemistry. Over 50 examples of C−H functionalizations using CO2 or ketones illustrate a broad applicability. The method opens new opportunities for late-stage C−H carboxylation and valorization of common arenes.