Asymmetric Epoxidation of alpha,beta-Unsaturated Ketones Catalyzed by Chiral Polybinaphthyl Zinc Complexes: Greatly Enhanced Enantioselectivity by a Cooperation of the Catalytic Sites in a Polymer Chain.
Polybinaphthyl zinc catalysts have been developed for the asymmetric epoxidation of alpha,beta-unsaturated ketones in the presence of tert-butyl hydroperoxide. Up to 81% ee has been achieved for the epoxidation of alpha,beta-unsaturated ketones containing beta-aliphatic substituents by using a binaphthyl polymer combined with diethylzinc. A very interesting positive cooperative effect of the catalytic sites in the polymer chain is observed which leads to greatly increased enantioselectivity over the corresponding monomer ligands.
Yu
Hong-Bin
HB
Department of Chemistry, University of Virginia, Charlottesville, Virginia 22901.
Zheng
Xiao-Fan
XF
Lin
Zhi-Ming
ZM
Hu
Qiao-Sheng
QS
Huang
Wei-Sheng
WS
Pu
Lin
L