Asymmetric Epoxidation of α,β-Unsaturated Ketones Catalyzed by Chiral Polybinaphthyl Zinc Complexes: Greatly Enhanced Enantioselectivity by a Cooperation of the Catalytic Sites in a Polymer Chain

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Abstract
Polybinaphthyl zinc catalysts have been developed for the asymmetric epoxidation of α,β-unsaturated ketones in the presence of tert-butyl hydroperoxide. Up to 81% ee has been achieved for the epoxidation of α,β-unsaturated ketones containing β-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.