Salt‐Free Strategy for the Insertion of CO 2 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 CO 2 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.