大位阻烯烃不对称环氧化合成手性环氧化合物

采用大位阻的有机锂试剂或格氏试剂与卤代烯烃偶联合成了7种大位阻取代烯烃. 以Oxone(KHSO5)作为氧化剂, 分别在D-果糖衍生酮和(2S,5R)-2-异丙基-5-甲基环己酮为催化剂的催化下, 将合成的7种大位阻取代烯烃转变成了7个大位阻的手性环氧化合物. 其中以D-果糖衍生酮的对映选择性最好, 当双键碳上含有3个取代基时, 对映选择性最高, e.e.值为96.8%~99.5%. (2S, 5R)-2-异丙基-5-甲基环己酮的对映选择性较差, 无论是一取代的烯烃还是三取代的烯烃, 其e.e.值均介于25.6%~34.1%之间.

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 oxideor 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%).