Chiral bis(oxazoline)–copper complex catalyzed Diels–Alder reaction in ionic liquids: remarkable reactivity and selectivity enhancement, and efficient recycling of the catalyst

Ionic liquid was found to be an excellent medium for asymmetric Diels–Alder reaction catalyzed by chiral bis(oxazoline)–copper complex. The reactivity and selectivity of reactions were highly dependent upon the property of the ionic liquids. Reactions of β-substituted acryloyl dienophiles in [Bmim]SbF6 at ambient temperature provided remarkably enhanced reactivity and stereoselectivity compared to homogeneous reactions in non-ionic liquid solvent at −78 °C. Due to the increased reactivity, the amount of metal catalyst could be reduced down to 0.6 mol % without any significant selectivity compromise. Additionally, recycling of the ligand–metal complex was achieved efficiently up to 18 times.