ABSTRACT
Centrally chiral bisoxazolines connected directly to a planar chiral [2.2]paracyclophane backbone were synthesized and evaluated as asymmetric ligands in Cu-catalyzed intermolecular ethanolic O-H insertion reactions of α-diazo esters. The reactivities and enantioselectivities of Cu complexes of the synthesized bisoxazoline ligands were lower than those of ligands without central chirality. However, planar chiral [2.2]paracyclophane-based bisoxazoline ligands with an inserted benzene spacer that had a sterically demanding isopropyl substituent showed good enantioselectivities in inter- and intramolecular aromatic O-H insertion reactions, without the aid of central chirality.
Subject(s)
Copper/chemistry , Drug Design , Hydroxides/chemistry , Polycyclic Compounds/chemistry , Polycyclic Compounds/chemical synthesis , Catalysis , Ligands , Molecular Structure , StereoisomerismABSTRACT
C2-symmetric planar chiral [2.2]paracyclophane-based bisoxazoline ligands, characterized by the inserted benzene spacer, which has a sterically demanding substituent, were synthesized and it was shown that up to 80% ee was obtained for the Cu-catalyzed O-H insertion reaction of α-diazo esters without the aid of the central chirality.