Synthesis of optically active α-hydroxycarbonyl compounds by (salen)Mn(III)-catalyzed oxidation of silyl enol ethers and silyl ketene acetals

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Optically active α-hydroxy ketones and esters have been prepared by (salen)Mn(III)-catalyzed asymmetric oxidation of silyl enol ethers and silyl ketene acetals in high enantioselectivity, with ee values up to 81 % for the α-hydroxy ketones and up to 57% for α-hydroxy esters. The extent of conversion and the enantioselectivity depends strongly on the type of oxygen donor, the pH of the aqueous bleach medium, the additive, and the substitution pattern at the enol functionality.