SYNTHESIS OF OPTICALLY-ACTIVE ALPHA-HYDROXY KETONES BY ENANTIOSELECTIVE OXIDATION OF SILYL ENOL ETHERS WITH A FRUCTOSE-DERIVED DIOXIRANE

Optically active alpha-hydroxy ketones 3 have been prepared in moderat e to high enantioselectivities by the asymmetric oxidation of the sily l enol ethers 2 with in situ generated dioxirane from the fructose-der ived ketone 1. Best results (ee values up to 82%) for this novel non-t ransition metal mediated asymmetric alpha-hydroxylation may be obtaine d, when an excess of the fructose-derived ketone 1 is employed at pH c a. 8 and short reaction times, Valuable mechanistic information on the spiro versus planar transition states for the oxygen-transfer process has been aquired through the absolute configuration of the resulting alpha-hydroxy ketone 3 products. (C) 1998 Elsevier Science Ltd. All ri ghts reserved.