VCD configuration of enantiopure/-enriched tetrasubstituted alpha-fluoro cyclohexanones and their use for epoxidation of trans-olefins.

The configurations of three enantiopure tetrasubstituted alpha-fluoro cyclohexanones (-)-5Ia, (-)-5IIa and (-)-6a were determined by VCD and proved to be (-)-(2S,5R)-5Ia, (-)-(2R,5R)-5IIa, and (-)-(2R,5R)-6a. The VCD study also identified the conformers populated in CDCl3 solution, including higher-energy gas-phase conformers with equatorial fluorine for 5Ia and 5IIa that are stabilized in CDCl3 solution. Used as catalysts for epoxidation of trans olefins (beta-methylstyrene, stilbene, methyl p-methoxy cinnamate) by oxone, it was found that (-)-5Ia is the most efficient for all trans olefins (providing, respectively, 62%, 90% and 66% ee) but that all three ketones provide high ee% with stilbene (78-90% ee). Moreover, the configurations predicted from the stereo outcome of the epoxidation reaction are identical to those determined by VCD.

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).