DBU and copper(I) mediated carboxylation of terminal alkynes using supercritical CO2 as a reactant and solvent

An organic solvent free, DBU (1,8-Diazabicyclo[5.4.0]undec-7-ene)-mediated and copper(I)-catalyzed CH activating carboxylation of terminal alkynes in supercritical CO2 (ScCO2) was developed in this work. Terminal alkynes react with ScCO2 in the presence of CuI/DBU and produce the corresponding functionalized propiolic acids in excellent yields. Under the optimized conditions, carbon dioxide can act as both reactant and solvent for the reaction. DBU serves as a ligand of copper catalyst, nucleophile, and base during the reaction. DBU alone can also mediate the direct CH carboxylation in the absence of transit metal catalyst. But the reaction requires a higher reaction temperature and pressure to obtain desired yields.