Catalytic Asymmetric Epoxidation of Chalcones

Significance

The authors reported the catalytic asymmetric epoxidation of chalcones using poly(ethylene glycol)-supported Cinchona ammonium salts. Thus, for example, the PEG-supported quinine 1 was prepared by reaction of quinine and bis(chloroacetamide)-PEG₂₀₀₀ in refluxing chloroform for 100 h. Asymmetric epoxidation of chalcone was carried out with 1, t-BtOOH (CH₂Cl₂ solution) and aqueous alkaline under biphasic conditions to give epoxide 2 in 96% yield with 86% ee. The polymer-supported catalyst was recovered and readily reused three times with slightly reduced catalytic activity (93% yield for third use). Ten substrates were examined (19-86% ee).