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submitted on 16.06.2020 and posted on 17.06.2020by Matthias Schmalzbauer, Thomas D. Svejstrup, Florian Fricke, Peter Brandt, Magnus J. Johansson, Giulia Bergonzini, Burkhard Koenig
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.