Copper- and copper-N-heterocyclic carbene-catalyzed C[horizontal line]H activating carboxylation of terminal alkynes with CO₂ at ambient conditions

The use of carbon dioxide as a renewable and environmentally friendly source of carbon in organic synthesis is a highly attractive approach, but its real world applications remain a great challenge. The major obstacles for commercialization of most current protocols are their low catalytic performances, harsh reaction conditions, and limited substrate scope. It is important to develop new reactions and new protocols for CO₂ transformations at mild conditions and in cost-efficient ways. Herein, a copper-catalyzed and copper-N-heterocyclic carbene-cocatalyzed transformation of CO₂ to carboxylic acids via C[horizontal line]H bond activation of terminal alkynes with or without base additives is reported. Various propiolic acids were synthesized in good to excellent yields under ambient conditions without consumption of any organometallic or organic reagent additives. This system has a wide scope of substrates and functional group tolerances and provides a powerful tool for the synthesis of highly functionalized propiolic acids. This catalytic system is a simple and economically viable protocol with great potential in practical applications.