ENANTIOSELECTIVE OXIDATION OF CHIRAL TITANIUM ENOLATES DERIVED FROM PROPIOPHENONE BY DIMETHYLDIOXIRANE OR 3-PHENYL-2-PHENYLSULFONYLOXAZIRIDINE

The stereoselective oxidation of the optically active titanium enolate complexes 2 of propiophenone by dimethyldioxirane (3) (as acetone solution) and 3-phenyl-2-phenylsulfonyloxaziridine (4) has been investigated. The chiral titanium enolates 2 were synthesized by the reaction of the lithium enolate of propiophenone and the respective optically active chlorotitanate complexes 1. For 3 as oxidant, the stereoselectivity of the alpha hydroxylation strongly depends on the substitution pattern at the central titanium atom and reached for the best case, namely 2 e, an enantiomeric excess (ee) of 63 %. Solvent and temperature exhibited only small effects on the stereoselectivity. Compound 4 as oxidant gave lower enantiomeric excesses than 3.