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Two novel soluble polymer-bound oligo-L-leucines 2 and 5, which can be retained by a membrane reactor system, have been prepared and used as catalysts for the continuously operated asymmetric epoxidation of chalcone. The optimized batch reaction conditions yield epoxychalcone in high enantioselectivities (up to 94%) and conversions (over 99%) after 15 minutes.Epoxides are widely used compounds in organic synthesis. 1 For this reason several approaches to effect enantioselective epoxidation have been made. 2 Among the welldeveloped methods, the Juliá-Colonna epoxidation, which utilizes chiral polyamino acids (in particular poly-L-leucine) as heterogeneous catalysts, has emerged as the first reliable method for the asymmetric epoxidation of electron-deficient olefins, exhibiting exceptionally high chiral induction for chalcone. 3Degussa and their partners from the University of Liverpool have worked intensively on the improvement of heterogeneous Juliá-Colonna oxidation. A noteworthy modification includes the introduction of percarbonate in dimethoxyethane as a cheap oxidant/solvent system for the use in some polyamino acid-catalysed epoxidations. 4The poly-L-leucine catalyst remained insoluble under all the reaction conditions applied. The first homogeneous version of the Juliá-Colonna epoxidation of trans-chalcone was reported recently. 5 However, the conversion observed was only 39% after 1 hour and 80% after 24 hours with an ee of 95-98%.Since the chiral information has to be transferred from the catalyst to the olefinic substrate, homogeneous asymmetric catalysis is a more attractive method for the synthesis of chiral epoxides. However, up to now, no process has made the step from an academically promising method to an application on larger scale.The interest of Degussa in developing methods for asymmetric synthesis in a chemzyme membrane reactor 6 promoted further investigation of the homogeneous enantioselective epoxidation of a,b-unsaturated ketones.We reasoned that the preparation of polymer enlarged oligo(L-leucine)s which were soluble in common organic solvents and large enough to be retained in a membrane reactor could allow us to develop a continuously operated asymmetric epoxidation of trans-chalcone.There are two major approaches to synthesize homogeneously soluble polymer-enlarged catalysts, that is using either linear polymers or dendrimers as carriers.We have focused our work on linear polymers, because they demand less synthetic effort. Thus, we prepared two types of soluble polymer enlarged oligo(L-leucine)s 2 and 5 (Scheme 1, Scheme 2). The approach to catalyst 2 involved the co-polycondensation of 1 equivalent of commercially available O,O-bis(2-aminoethyl)-polyethyleneglycol 20000 1 with 16 equivalents of L-leucine-N-carboxyanhydride in CHCl 3 . 7 Scheme 1 Synthesis of homogeneously soluble oligo(L-leucine) 2.We found that the resulting polyethyleneglycol-supported oligo(L-leucine) 2 can act as an efficient homogeneous chiral catalyst in the epoxidation of trans-chalcone 6 employing the urea ...

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