Epoxidation of p-Methoxycinnamates Using Chiral Dioxiranes Derived from New Trisubstituted Halogenated Cyclohexanones: Enhanced Efficiency of Ketones Having an Axial Halogen

Abstract

Epoxidation of p-methoxycinnamates using substoichiometric amounts of chiral and enantiopure dioxiranes generated in situ from chiral trisubstituted chloro and fluoro cyclohexanones showed that ketones with an axial Cl or F were more efficient than ketones with an equatorial Cl or F, that increasing the steric hindrance in the alpha-position (isopropyl instead of methyl) decreased the efficiency, and that the alpha-fluoro ketone 5a (axial fluorine) was the most efficient (82% conversion and 46% ee in (-)-epoxide).