Epoxidation of p-methoxycinnamates using chiral dioxiranes derived from new trisubstituted halogenated cyclohexanones: enhanced efficiency of ketones having an axial halogen
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).
Solladie-Cavallo
A
Laboratoire de Stereochimie Organometallique associe au CNRS, ECPM/Universite Louis Pasteur, 25 rue Becquerel, 67087 - Strasbourg Cedex 2, France.
Bouerat
L