Design of task-specific ionic liquids for catalytic conversion of CO ₂ with aziridines under mild conditions

A series of polyethylene glycol (PEG)-functionalized ionic liquids (ILs) were developed as recyclable and efficient catalysts for selective synthesis of 5-aryl-2-oxazolidinones from aziridines and CO₂ without addition of any organic solvents or additives. In particular, high yields, chemo- and regio-selectivities of oxazolidinones were attained when BrDBNPEG ₁₅₀DBNBr (DBN: 1,5-diazabicyclo[4.3.0]non-5-ene) was used as the catalyst, presumably due to activation of CO₂ by the ether linkage in the PEG backbone, and stabilization of the ring-opened species of aziridine by the delocalized cation BrDBNPEG₁₅₀DBN⁺. Furthermore, the catalyst could be reused for over four consecutive cycles without appreciable loss of catalytic activity and selectivity. The effects of catalyst structure and various reaction parameters on the catalytic performance were also investigated in detail. It was demonstrated that the catalyst worked well for a variety of aziridines producing the corresponding oxazolidinones in good yields and excellent regio-selectivities. Therefore, this solvent-free process could thus represent an environmentally friendly approach for ILs-catalyzed conversion of CO₂ into value-added chemicals.