Morifumi Fujita

An oxetane intermediate during a direct aldol reaction was trapped with an internal aryl group to yield trans-tetraline products. The contribution of the oxetane intermediate was confirmed by 18O-isotope labeling experiments.

<p>The substitutions at the 2′- and/or 6′-positions of the quinoline ring of cinchonidine reduce both the intrinsic enantioselectivity and adsorption strength for the enantioselective hydrogenation of α-phenylcinnamic acid over Pd/C.</p>

© 2020 The Chemical Society of Japan. Enantioselective hydrogenations of α,β-unsaturated carboxylic acids over cinchona alkaloid-modified Pd metal heterogeneous catalysts have received considerable attention because of scientific importance in molecular recognition catalysis as well as feasibility of industrial applications. In the present study, comprehensive kinetic analysis of the hydrogenation was conducted to disclose the crucial kinetic parameters controlling enantiodifferentiation and reaction rate with the combinations of four kinds of modifier and three kinds of substrate. Despite simplicity of the kinetic model, the present novel kinetic formulation allows us to describe the enantioselectivity as a function of modifier concentration, to estimate intrinsic enantioselectivity at the modified sites, to estimate respective reaction rates at the modified and unmodified sites, and to establish a correlation between the magnitude of ligand acceleration and kinetic parameters. The enantioselectivity is successfully correlated to the reaction rate. The adsorption strength of the modifier on Pd is suggested to decrease in the order, cinchonidine > cinchonine > quinine > quinidine. The roles played by benzylammine and the observed decrease in the selectivity at a high modifier concentration are also discussed. The kinetic model and formulation can be applied to analyze the catalytic behaviors and performance of Pt counterparts.

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. Abstract: The asymmetric hydrogenation of (E)-2,3-di(4-methoxyphenyl)propenoic acid was conducted over Pd/C chirally modified with cinchona alkaloids methyl-substituted at 2′-position of the quinoline ring. It is revealed that the adsorption strength of the modifiers and the intrinsic enantioselectivity at the modified sites are decreased by the methyl-substitution. The intrinsic enantioselectivity of the modifier is correlated to kinetic parameters. Graphic Abstract: [Figure not available: see fulltext.]

© 2019 The Chemical Society of Japan To ensure high enantiopurity of the product, enantio-differentiating hydrogenation of methyl acetoacetate over a (R,R)-tartaric acid-modified Raney nickel catalyst is normally performed under elevated H2-pressure (310 MPa). In this study, higher enantioselectivity than previously reported for methyl acetoacetate was achieved (92% ee) under low H2pressure of 0.42 MPa. Effects of reaction conditions on the enantioselectivity and hydrogenation rate were investigated using a low-pressure reaction system (<0.5 MPa of H2). It was found that impurities in the solvent greatly reduce the enantioselectivity of MAA. The low-pressure reaction system enabled a satisfactory kinetic approach. The reaction rate was well described by Langmuir-Hinshelwood formalism, verifying the previous assumption that the addition of adsorbed hydrogen to the substrate interacting with surface tartrate is a rate-determining step.