Salt‐Free Strategy for the Insertion of CO2 into C−H Bonds: Catalytic Hydroxymethylation of Alkynes

A copper(I) catalyst enables the insertion of carbon dioxide into alkyne C−H bonds by using a suitable organic base with which hydrogenation of the resulting carboxylate salt with regeneration of the base becomes thermodynamically feasible. In the presence of catalytic copper(I) chloride/4,7‐diphenyl‐1,10‐phenanthroline, polymer‐bound triphenylphosphine, and 2,2,6,6‐tetramethylpiperidine as the base, terminal alkynes undergo carboxylation at 15 bar CO2 and room temperature. After filtration, the ammonium alkynecarboxylate can be hydrogenated to the primary alcohol and water at a rhodium/molybdenum catalyst, regenerating the amine base. This demonstrates the feasibility of a salt‐free overall process, in which carbon dioxide serves as a C1 building block in a C−H functionalization. A catalytic system consisting of CuI/BPhen allows the carboxylation of terminal alkynes with CO2 with such a mild amine base that it becomes thermodynamically feasible to hydrogenate the resulting ammonium carboxylates to the corresponding alcohols under regeneration of the amine base. This provides proof of concept for salt‐free processes utilizing CO2 as a C1 building block in C−C bond formation (see scheme).