Asymmetric epoxidation of olefins presents a powerful strategy for the synthesis of enantiomerically enriched epoxides. [1][2][3] For the epoxidation of unfunctionalized cis-olefins, chiral salen and porphyrin complexes give very high enantioselectivities. Jacobsen's Mn salen catalyst is particularly successful and practical. Dioxiranes generated in situ from chiral ketones have been shown to be highly enantioselective for the asymmetric epoxidation of trans-olefins and trisubstituted olefins. 4-6 However, highly enantioselective epoxidation of cis-olefins using chiral dioxiranes still remains a challenging problem. Herein we wish to report our preliminary efforts on this subject.Recently, we reported that the fructose-derived ketone 1 is an effective epoxidation catalyst and gives high ee values for a variety of trans-olefins and trisubstituted olefins (eq 1). 6 However, epoxidation of cis-olefins using this ketone led to rather poor enantioselectivity. 6c For example, a 39% ee was obtained for cisβ-methylstyrene, giving the (1R,2S) epoxide as the major enan-

This paper describes a new class of chiral oxazolidinone ketone catalyst for asymmetric epoxidation. High ee values have been obtained for a number of cyclic and acyclic cis-olefins. The epoxidation was stereospecific with no isomerization observed in the epoxidation of acyclic systems. Encouragingly high ee values have also been obtained for a number of terminal olefins. Mechanistic studies show that electronic interactions play an important role in stereodifferentiation.

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