Synthesis of Bulky Epoxides via Asymmetric Epoxidation of Bulky Olefins

It has been found that the optically active epoxide (S)-4,4,4-triphenyl-1-butene oxide [or its (R) isomer], which bears bulky pendant, can be polymerization to form helical polyether. To obtain the helical structure information of other polyethers bearing bulky pendant, the method for synthesis of optically active bulky epoxide with multifarious structure is necessary. The optically active bulky epoxide which contains a methene between the bulky group and epoxy group has been synthesized by coupling a bulky alkyllithium and optically active epichlorohydrin. However, this method is not suitable for the synthesis of other optically active bulky epoxides. In this article, seven chiral epoxides with high e. e. value were synthesized via synthesizing bulky olefins at first and then converting the olefins to the corresponding optical epoxides with oxone (KHSO5) as an oxidant and a chiral ketone as a catalyst. The D-fructose ketone derivant had high enantioselectivity to epoxidation of trisubstituted olefins (the e.e. values of epoxides were 96.8%-99.5%), but its enantioselectivity to the epoxidation of monosubstituted olefins was not good. (2S,5R)-2-Isopropyl-5-methylcyclohexanone also showed an enantioselectivity to the epxidation of olefins but the enantioselectivity was poor in spite of the cases of monosubstituted, disubstituted or trisubstituted olefins (the e. e. values of epoxides were 25.6%-34.1%).