A Highly Diastereoselective and Enantioselective Phase-Transfer Catalyzed Epoxidation of β-Trifluoromethyl-β,β-disubstituted Enones with H۲O۲

Trifluoromethylated organic compounds, especially chiral quaternary alcohols bearing trifluoromethyl group are of important intermediates in drugs, agrochemicals and etc.An efficient epoxidation of β-CF۳-β,β-disubstituted unsaturated ketones (۶) has been developed with environmental benign hydrogen peroxide as the oxidant and F۵-substituted chiral quaternary ammonium salt (۱g or ۵) derived from cinchona-alkaloid as the catalyst. Using ۳ mol% of the catalyst, both enantiomers of(R,R) and (S,S) β-trifluoromethyl-α,β-epoxy ketones (۷, ۸) were obtained in excellent diastereoselectivities (up to ۱۰۰:۱ d.r.) and enantioselectivities (up to ۹۹.۷% ee). The effects of catalyst structure, catalyst loading, substrate structure, the nature of oxidant, and reaction conditions on the catalyst capacities have been discussed in full length. The reaction mechanism was proposed to explain the origin of chiral induction. By subsequent reduction with zinc the epoxides are exhibited to be converted into trifluoromethylated quaternary alcohols without any loss in enantioselectivities. All new compounds are fully characterized by IR, NMR, elemental analysis and or high resolution mass spectrum.

کلیدواژه ها:

Asymmetric catalysis ، Epoxidation ، Hydrogen peroxide ، Phase transfer catalyst ، Trifluoromethyl