Asymmetric C-H oxidation of vic-diols to alpha-hydroxy ketones by a fructose-derived dioxirane: Electronic effects on the enantioselectivity of oxygen transfer

A mechanistic study on the enantioselective C-H oxidation of vic-diols with the in-situ-generated dioxirane from the fructose-derived ketone 1 is pres ented. The asymmetrization of meso-configured and the kinetic resolution of racemic vie-diols 2 afforded the optically active alpha-hydroxy ketones 3 in opposite configurations with moderate to good ee values. Significant ele ctronic effects on the enantioselectivity of C-H insertion have been observ ed, which are explained in terms of the hydrogen-bonded transition-state st ructures for the concerted C-H oxygen insertion.