Surface Confinement Effects on Enantioselective Cyclopropanation. Reactions with Supported Chiral 8-Oxazolinylquinoline−Copper Complexes

Abstract

Chiral quinolinoxazoline ligands, a class of C1-symmetric chiral ligands, are tested in the enantioselective supported catalysis of a cyclopropanation reaction, trying to improve surface confinement effects of the clay support on the reaction stereoselectivity. In the case of trans/cis diastereoselectivity, these surface effects lead to a complete reversal of selectivity, with cis selectivity values superior to those previously found using C2-symmetryic bisoxazoline ligands. On the other hand, the enantioselectivities do not display important variations in the supported catalysts. A theoretical (DFT) mechanistic study is carried out to explain the origin of the enantioselectivity in homogeneous phase at a molecular level