Heterogeneous Organocatalytic Synthesis of Propargylic Esters Using a Polymer-Supported N-Heterocyclic Carbene.

The conversion of carbon dioxide into high-value chemical scaffolds is a central challenge in modern green chemistry. In this study, we report the first heterogeneous, metal-free organocatalytic protocol for the three-component synthesis of propargylic esters from terminal alkynes, CO2, and alkyl halides, employing a vinyl addition polynorbornene (VA-PNB)-supported N-Heterocyclic Carbene (NHC) precatalyst. Optimization studies revealed that the immobilized tert-butyl-substituted NHC outperforms other structural variants, promoting the carboxylative coupling under metal-free conditions. The catalyst can be recovered by filtration and regenerated through mild acid treatment. A gradual decrease in activity is observed upon reuse due to retained potassium carbonate used as a base in the reaction, but the catalyst activity can be recovered with further washing. The method demonstrates excellent chemoselectivity with cinnamyl-type electrophiles, offering a sustainable and operationally simple approach to valuable functionalized esters, without the need for transition metals.