Carboxyl group is one of the most widely used groups in organic synthesis. Herein, an efficient copper‐catalyzed carboxylation of aryl thianthrenium salts with carbon dioxide (CO2) at room temperature has been developed. The reaction employs low loading of cuprous chloride catalyst under 1 atm CO2 and exhibits good functional group tolerance. In combination with C−H thianthrenation of aromatic hydrocarbons, this work provides an efficient method for the site‐selective C−H carboxylation of aromatic hydrocarbons. It may serve as a significant late‐stage carboxylation tool for the modification of drug molecules in the future.

The Grignard-type nucleophilic addition of C(sp 2 )−H bonds to aldehydes catalyzed by high-oxidation-state transition metal complexes is limited to activated aldehydes. Herein, we report the first example of Grignard-type nucleophilic addition of C(sp 2 )−H bonds to unactivated aldehydes catalyzed by high-oxidation-state ruthenium(II). The reaction has mild reaction conditions and good functional group tolerance. The corresponding alcohol products are obtained in good to excellent yields.

Carboxyl group is one of the most widely used groups in organic synthesis. Herein, an efficient copper‐catalyzed carboxylation of aryl thianthrenium salts with carbon dioxide (CO2) at room temperature has been developed. The reaction employs low loading of cuprous chloride catalyst under 1 atm CO2 and exhibits good functional group tolerance. In combination with C−H thianthrenation of aromatic hydrocarbons, this work provides an efficient method for the site‐selective C−H carboxylation of aromatic hydrocarbons. It may serve as a significant late‐stage carboxylation tool for the modification of drug molecules in the future.