Epoxidation of olefins was carried with an excellent yield by dioxiranes generated in situ by reaction of ketone with H 2O 2 in the presence of NaHCO 3 in mixed solvent of acetonitrile and water. The catalytic activity of various ketones on epoxidation was studied for the first time. It is found that the ketone with electron withdrawing group has an excellent catalytic activity and trifluromethyl ketone has the highest catalytic activity. Some bulky ketones with electron withdrawing group show a very low catalytic activity. For olefins, the electron withdrawing group decreased the reactivity of the olefin and the electron donating group increased the reactivity, but the steric factor has little effect on the reactivity of olefins.
Asymmetric epoxidation of olefins with oxone was first catalyzed by chiral iminium salts generated in situ from chiral amines and aldehydes. With 2S,5S-2,5-dicyclohexylaminocarbonylpyrolidine and t-butylacetaldehyde, trans-stilbene were epoxdized in 80% conversion, 93% yield and 65% e.e. at 0 ℃.
The NMR spectra revealed that the calixarene frame of 1, 3-disubstituted calix[4]arenes bearing optically active groups is asymmetric, even without the formation of a sub-ring. This inherent chirality arises from the interaction of the two chiral groups, which hinder the substituents’ free rotation. Thus, these chiral calix[4]arenes display good chiral recognition ability.
