Chiral Cu(II) Complexes as Recyclable Catalysts for Asymmetric Nitroaldol (Henry) Reaction in Ionic Liquids as Greener Reaction Media

摘要

Abstract Chiral Cu (II) complexes generated in situ from C₂-symmetric chiral secondary bis-amines 1′–4′ based on 1,2-diaminocyclohexane structure having H, t-Bu and Cl substituents at 3, 3′, 4, 4′ and 5, 5′ with copper acetate. They were used as catalysts for an environmentally benign protocol for highly enantioselective nitroaldol reaction of various aldehydes with nitromethane in the presence of different ionic liquids as a greener reaction medium at 0 °C. Excellent yields (up to 90% with respect to aldehyde) of β-nitroalcohols with high enantioselectivity (ee, up to 94%) was achieved when [emim]BF₄ was used as ionic liquid. The present ionic liquid mediated nitroaldol protocol is recyclable (up to five cycles) with no significant loss in its performance.