Asymmetric epoxidation of cis-alkenes with arabinose-derived ketones: enantioselective synthesis of the side chain of Taxol

The ee values of asymmetric epoxidation of cis-ethyl cinnamate 15 with arabinose-derived ketones as catalyst and Oxone^® as the terminal oxidant were found to increase inversely with the size of the catalyst acetal blocking group. Ketone catalyst 2, with the least bulky methoxy acetal group, displayed the best enantioselectivity and afforded ethyl (2R,3R)-3-phenylglycidate 16 in 68% ee. Epoxide 16 was readily converted into a protected side chain of Taxol^® in five steps with an overall yield of 89%. The enantioselectivity of the epoxidation of other cis-alkenes was moderate to poor.