VCD configuration of enantiopure/‐enriched tetrasubstituted α‐fluoro cyclohexanones and their use for epoxidation of trans ‐olefins

The configurations of three enantiopure tetrasubstituted α‐fluoro cyclohexanones (–)‐ 5Ia, (–)‐ 5IIa and (–)‐ 6a were determined by VCD and proved to be (–)‐(2 S ,5 R )‐ 5Ia, (–)‐(2 R, 5 R )‐ 5IIa, and (–)‐(2 R ,5 R )‐ 6a. The VCD study also identified the conformers populated in CDCl 3 solution, including higher‐energy gas‐phase conformers with equatorial fluorine for 5Ia and 5IIa that are stabilized in CDCl 3 solution. Used as catalysts for epoxidation of trans olefins (β‐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. Chirality 16:467–474, 2004. © 2004 Wiley‐Liss, Inc.