Synthesis of Propiolic Acids via Copper-Catalyzed Insertion of Carbon Dioxide into the C-H Bond of Terminal Alkynes

A highly effective copper catalyst has been developed that promotes the insertion of carbon dioxide into the C-H bond of terminal alkynes under unprecedentedly mild conditions. For the first time, propiolic acids can thus be synthesized in excellent yields from alkynes and carbon dioxide in the presence of the mild base cesium carbonate. The catalyst, (4,7-diphenyl-1,10-phenanthroline) bis[tris(4-fluorophenyl)phosphine]-copper(I) nitrate, is easy accessible and relatively stable against air and water.