ABSTRACT
Chemical Research Center, Hungarian Academy of Sciences, 1025 Budapest, Pusztaszeri út 59-67 Hungary; joemarg@chemres.hu
Abstract Enantioselective hydrogenation of 2,3-butanedione and 3,4-hexanedione has been studied over different type of supported Pt catalysts (Pt/Al2O3, Pt/SiO2, Pt/MCM-41) in the presence of cinchonidine (CD). Kinetic results confirmed that (i) 2,3-butanedione is more reactive than 3,4-hexanedione over all catalysts studied and (ii) both substrates have a strong poisoning effect. The kinetic results confirmed also that CD concentration close to 10-3 M is necessary to achieve both high reaction rate and enantioselectivity in the range of 55-65 %. NMR results confirmed that substrate-modifier interaction takes also place in the liquid phase. Introduction The asymmetric hydrogenation (AH) of prochiral compounds, in particular diketones (see Figure 1) and α-ketoesters, is of significant importance since they are convenient building blocks in the asymmetric synthesis of biologically active compounds. [1-4]. The most frequently studied reaction of this class is the hydrogenation of α-ketoesters to the corresponding α-hydroxy esters [1]. The best catalyst system of this reaction is Pt/Al2O3 modified with cinchonidine (see Figure 2). High performances have been reported for Pt-cinchona catalyst systems in which Pt has been supported on silica, alumina, and carbon [5] or deposited in zeolites [6] and in mesopores of MCM-41 [7].
