Reaktivit�t und Selektivit�t bei der Oxidation von Styrolderivaten, II. Untersuchungen zur Oxidation vonp-substituierten ?-Methylstyrolen
摘要:
The liquid phase oxidation of p-substituted (Br-, Cl-, t-Bu-, MeO-, CF3-) alpha-methylstyrenes and of alpha,p-dimethoxystyrene with pure oxygen was investigated in chlorobenzene solution and in presence of cumene and of cumene hydroperoxide in the temperature range 65-125 degrees C. The product yields were determined gaschromatographically. The differences of the activation energies of the epoxide formation and the parallel reactions amount to 19-48 kJ/mol. The epoxide selectivity increases with increasing temperature and concentration of olefine. The relative chain propagation constants k(p) (C=C) Were determined by competitive oxidation with cumene. The k(p)(C=C) values of p-substituted alpha-methylstyrenes can be correlated by the Hammett equation with both sigma and sigma(+) substituent constants.
Resolution of Diols via Catalytic Asymmetric Acetalization
作者:Ji Hye Kim、Ilija Čorić、Chiara Palumbo、Benjamin List
DOI:10.1021/ja512481d
日期:2015.2.11
A highly enantioselective kinetic resolution of diols via asymmetricacetalization has been achieved using a chiral confined imidodiphosphoric acid catalyst. The reaction is highly efficient for the resolution of tertiary alcohols, giving selectivity factors of up to >300. Remarkably, even in cases where the selectivity factors are only moderate, highly enantioenriched diols are obtained via a stereodivergent
Herein, we report the first alkylative kineticresolution of vicinal alcohols realized by cooperative use of a chiral quaternary ammonium salt and an achiral borinic acid. In addition, a catalytic regioselective alkylation of a secondary alcohol in the presence of an unprotected primary one is presented, emphasizing the unique selectivity and potential of this ammonium borinate catalysis.
Tiffeneau, Comptes Rendus Hebdomadaires des Seances de l'Academie des Sciences, 1910, vol. 150, p. 1183
作者:Tiffeneau
DOI:——
日期:——
A Simple Primary Amine Catalyst for Enantioselective α-Hydroxylations and α-Fluorinations of Branched Aldehydes
作者:Michael R. Witten、Eric N. Jacobsen
DOI:10.1021/acs.orglett.5b01193
日期:2015.6.5
A new primary amine catalyst for the asymmetric a-hydroxylation and a-fluorination of alpha-branched aldehydes is described. The products of the title transformations are generated in excellent yields with high enantioselectivities. Both processes can be performed within short reaction times and on gram scale. The similarity in results obtained in both reactions, combined with computational evidence, implies a common basis for stereoinduction and the possibility of a general catalytic mechanism for a-functionalizations. Promising initial results in alpha-amination and alpha-chlorination reactions support this hypothesis.