Hydrogenation of 1-phenyl-1,2-propanedione over Pt catalysts modified by cinchona alkaloid O -ethers and the kinetic resolution of the 1-hydroxyketones generated

摘要

Nine cinchona alkaloid O -ethers together with cinchonidine and cinchonine were studied as chiral modifiers in the enantioselective hydrogenation of 1-phenyl-1,2-propanedione over Pt/Al2O3.The influence of the O-substituent on the reaction rate,selectivity and product distribution was investigated.Apparent rate constants for all hydrogenation steps were calculated using a first-order kinetic approach resulting in a good agreement between the experimentally recorded and predicted concentrations.The experimentally observed structure-selectivity effects indicate that the mechanisms of enantiodifferentiation over the catalyst modified by parent cinchona alkaloids and their ether derivatives differ from each other.Moreover,the modifier structure-selectivity dependence and the solvent effect were different for enantio- and diastereoselection in the 1-phenyl-1,2-propanedione and 1-hydroxyketone hydrogenations.Correlation between the modifier substituent bulkiness and diastereoselectivity of the 1-hydroxyketone hydrogenation was observed.Data on the inversion of enantioselectivity of 1-phenyl-1,2-propanedione hydrogenation,diastereoselectivity and the sense of kinetic resolution of the 1-hydroxyketones were presented.Due to the complexity of the reaction network,several competing mechanistic pathways may be present in a single reaction system.