In Situ Generated Zinc(II) Catalyst for Incorporation of CO₂ into 2-Oxazolidinones with Propargylic Amines at Atmospheric Pressure

Incorporation of CO₂ into heterocyclic compounds (i.e., 2-oxazolidinones) under mild conditions, especially at atmospheric pressure still remains challenging. The mononuclear Zn^II complex ZnCl₂ (TBD)₂ , where TBD=1,5,7-triazabicyclo[4.4.0]dec-5-ene, in this study was demonstrated as a robust catalyst for the carboxylative cyclization of propargylic amines with CO₂ to exclusively afford various 2-oxazolidinones in excellent yields. Notably, the Zn^II catalytic species is readily generated in situ from ZnCl₂ and TBD without pre-preparation and further isolation. Such a CO₂ fixation protocol could proceed smoothly under atmospheric pressure at mild temperature in an atom economic and environmentally benign manner. ¹³ C NMR and control experiments were performed to explore the possible interaction between Zn^II and the carbon-carbon triple bond of propargylic amine. The dual catalytic role of the Zn catalyst to enhance O-nucleophilicity of the carbamate anion intermediate and activate the carbon-carbon triple bond is proposed based on mechanistic investigations.