催化量的氧化钙-硅胶对Sharpless烯丙醇不对称环氧化的影响

当在Sharpless试剂中加入催化量的金属氢化物和硅胶后, 烯丙醇的不对称环氧化反应时间大为缩短, 而化学和光学产率不受影响。着重讨论了氢化钙和硅胶对Sharpless烯丙醇不对称环氧化的作用。

The effect of catalytic amount of calcium hydride and silica gel on Sharpless asymmetric epoxidation

The reaction time of asym. epoxidn. of allylic al. was drastically reduced whereas the enantioselectivity increased when a catalytic amount of CaH2 and SiO2 was present in the Sharpless reagent. Transition state studies indicated a SN2 mechanism, in which the interaction between Ca2+ and O in the peroxide species accelerated the O-O bond cleavage and increased the reaction rate. The adsorbed Ca2+ on SiO2 prevented the decrease in enantioselectivity.