Base-free catalytic systems achieved via the design of copper complexes: synthesis of 2-oxazolidinones from propargylic amines and CO2

Five N-heterocyclic carbene–copper complexes were synthesized and used as catalysts to prepare 2-oxazolidinones via the carboxylation cyclization of CO₂ and propargylic amines. This catalytic system could perform broad substrates with a low catalyst loading of 0.75 mol% under no-solvent and base-free conditions and afforded 2-oxazolidinones as the target products in high yields under mild conditions (30–70 °C). The intermediate in the carboxylation cyclization of CO₂ and propargylic amines was monitored by in situ FT-IR spectroscopy and HRMS methods, and the reaction mechanism was elucidated, in which the coordinated Cu atom acted as the Lewis acidic center to activate propargylic amines and the uncoordinated nitrogen atom of pyridine acted as the Lewis basic center to activate CO₂.