Chiral bis(oxazoline) copper(II) complexes: Versatile catalysts for enantioselective cycloaddition, aldol, Michael, and carbonyl ene reactions

A bis(oxazoline) (box) copper(II) complex and its hydrated counterpart (1 a nd 2) function as enantioselective Lewis acid catalysts for carbocyclic and hetero Diels-Alder, aldol, Michael, ene, and amination reactions with subs trates capable of chelation through six- and five-membered rings. X-ray cry stallography of the chiral complexes reveals a propensity for the formation of distorted square planar or square pyramidal geometries. The sense of as ymmetric induction is identical for all the processes catalyzed by [Cu((S,S )-t-Bu-box)](X)(2) complexes 1 and 2 (X = OTf and SbF) resulting from the i ntervention of a distorted square planar catalyst-substrate binary complex. These catalyzed processes exhibit excellent temperature-selectivity profil es. Reactions catalyzed by [Cu(S,S-Ph-pybox)](SbF6)(2) and their derived ch elation complexes are also discussed.