Heterogeneous asymmetric epoxidation of cis-ethyl cinnamte over Jacobsen's catalyst immobilized in inorganic porous materials

摘要

(2R,3R)-cis-ethyl phenylglycidate obtained from cis-ethyl cinnamate enantioselective epoxidation is a very important intermediate for the synthesis of taxol and taxotère, drugs used for the treatment of breast, lung, and ovarian cancer. Among several catalytic methods, the homogeneous asymmetric epoxidation reported by Jacobsen and his colleagues is one of the most relevant methods. However the chiral catalyst, a Manganese(lll) salen complex coexists with the reaction products in one unique phase. This makes it difficult to separate the reaction products and catalyst reusability, two key features in the drive to develop an industrial process. Therefore many efforts have been made for the heterogenization of Jacobsen type catalysts either by using an inorganic or organic matrix as support material. Although, various heterogeneous systems have proved to be stable to leaching, catalyst degradation under prolonged oxidation conditions has limited the catalyst re-use. In this PhD work, the Jacobsen's catalyst has been immobilized on highly dealuminated zeolites X and Y, AI-MCM-41 and Si-MCM-41 using different methods. Mesopores completely surrounded by micropores were created inside the crystallites of zeolite X and Y. AI-MCM-41 and Si-MCM-41 were prepared by conventional methods. Using in situ generated DMD as oxygen source for the enantioselective epoxidation of olefins more reactive than c/s-ethyl cinnamate, the oxidative degradation of the catalyst could be prevented. Also, the un-immobilized catalyst proved to be partially recoverable. Here, the catalyst reuse gave an activity loss, although the initial enantioselectivity could be maintained through three cycles. The activity loss is associated with incomplete recovery of the catalyst rather than catalyst degradation. These results suggest that milder reaction conditions can be obtained with substrates easy to oxidize and with oxygen source prepared in situ. In this way, the reusability of the catalyst can be achieved powerfully.