Proposed Mechanism

Scheme 11 shows the proposed catalytic cycle and the most favored transition state for the chiral ketone based epoxidations in the presence of oxone as terminal oxidant.

Scheme 11

The chiral ketone-catalyzed epoxidation has been subsequently found to be effective using the combination of hydrogen peroxide and acetonitrile as an alternative oxidant. For example, chiral ketone 8 has been used for the epoxidation of a variety of alkenes with comparable yields and enantioselectivity (Scheme 12).

Proposed Mechanism

In this protocol, acetonitrile reacts with hydrogen peroxide to generate peroxyimidic acid and then reacts with the ketone to give the active dioxirane. Under these conditions, a stoichiometric amount of the amide is generated as a product.

Scheme 12