Recyclable copper catalysts based on ionic-tagged C2-symmetric Indabox ligands and their application in asymmetric Henry reactions Original Research Article

New imidazolium/pyrrolidinium-tagged Indabox ligands were designed and prepared. Catalysts based on these ligands with Cu(OAc)2·H2O were applied to the asymmetric Henry reaction using various aldehydes and CH3NO2, the products were obtained in high enantioselectivity. Specifically, (R)-1-(2-methoxylphenyl)-2-nitroethanol was obtained in 94% ee in MeOH. Furthermore, the catalyst based on 7 could be recycled at least 12 times by simple wash without an obvious loss of activity or enantioselectivity. This catalytic procedure demonstrated the potential for catalyst recyclability in the asymmetric Henry reaction. Additionally, a theoretical mechanistic study was conducted to explain the origin of the enantioselectivity.