Enantioselective synthesis and stereoselective rearrangements of enol ester epoxides

Enol eaters can be epoxdized with high enantioselectivities using the fruct ose-derived chiral ketone I as catalyst and Oxone as oxidant. A detailed st udy of enantiomerically enriched enol ester epoxides has revealed that the acid-catalyzed rearrangement can proceed through two distinct pathways, one with retention of configuration and the other with inversion. The competit ion between the two pathways is highly dependent upon the nature of the aci d catalyst. A strong acid favors retention of configuration and a weak acid favors inversion of configuration. Under thermal conditions, these epoxide s rearrange highly stereoselectively with inversion of configuration. Eithe r enantiomer of an alpha -acyloxy ketone can be formed from one enantiomer of an enol eater epoxide by judicious choice of reaction conditions.