Asymmetric oxidation of silyl enol ethers using chiral dioxiranes derived from a-fluoro cyclohexanones

Asymmetric oxidation of silyl enolethers derived from tetralone, 2-methyl-tetralone, propiophenone and deoxybenzoin using chiral dioxiranes generated in situ from oxone and new chiral a-fluorinated cyclohexanones or fructose-derived ketone have been studied. It was observed that tetrasubstituted silyl enolethers are poor substrates, that substitution at C8 of the fluoro-ketones has a significant effect on the enantioselectivities obtained and that the fructose-derived-ketone provides higher enantioselectivities. The absolute configuration of the major hydroxy ketones obtained can be rationalized using a spiro model proposed for epoxidation of olefins.