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41.
Although quaternary onium salt-catalyzed phase-transfer reactions are generally believed to require base additives, we discovered even without any base additives conjugate additions of 3-substituted oxindoles proceeded smoothly in the presence of lipophilic quaternary onium bromide under water-organic biphasic conditions. The mechanism of this novel base-free neutral phase-transfer reaction system was investigated, and the assumed catalytic cycle was presented together with interesting effects of water and lipophilicity of the phase-transfer catalyst. The base-free neutral phase-transfer reaction system could be applied to highly enantioselective conjugate additions, aldol reaction, sulfenylation, and chlorination under the influence of chiral bifunctional onium bromides as key catalysts. 相似文献
42.
[reaction: see text] The carboxylic acid catalyzed three-component aza-Friedel-Crafts reactions of aldehydes, primary amines, and indoles in water have been developed. The aza-Friedel-Crafts products could be easily transformed to various 3-substituted indoles including biologically active compounds. This system offers a novel efficient method for the synthesis of 3-substituted indoles. 相似文献
43.
Dr. Seiji Shirakawa Dr. Lijia Wang Dr. Rongjun He Dr. Satoru Arimitsu Prof. Dr. Keiji Maruoka 《化学:亚洲杂志》2014,9(6):1586-1593
Although phase‐transfer reactions catalyzed by using quaternary ammonium salts are generally believed to require base additives, we discovered that, even without any base additives, conjugate additions of 3‐substituted oxindoles to nitroolefins proceeded smoothly in the presence of lipophilic quaternary ammonium bromide under water–organic biphasic conditions. The mechanism of this novel base‐free neutral phase‐transfer reaction system is investigated and the assumed catalytic cycle is presented together with interesting effects of water and lipophilicity of the phase‐transfer catalyst. The base‐free neutral phase‐transfer reaction system can be applied to highly enantioselective conjugate addition and aldol reactions under the influence of chiral bifunctional ammonium bromides as key catalysts. The structure of the chiral ammonium enolate intermediate is discussed based on the single‐crystal X‐ray structures of relevant ammonium salts and the importance of bifunctional design of catalyst is clearly explained in the model of intermediate. 相似文献
44.
Shirakawa E Ikeda D Yamaguchi S Hayashi T 《Chemical communications (Cambridge, England)》2008,(10):1214-1216
Alkyl Grignard reagents were found to be isomerized to more stable ones in high isomerization ratios (>99%) under cooperative catalysis by iron and copper, which promote isomerization of alkyl groups and transmetalation between Fe-Mg, respectively. 相似文献
45.
46.
Shirakawa S Lombardi PJ Leighton JL 《Journal of the American Chemical Society》2005,127(28):9974-9975
A highly diastereo- and enantioselective [3 + 2] acylhydrazone-enol ether cycloaddition mediated by a simple chiral silane Lewis acid is described. The reactions are highly practical, as demonstrated by a larger scale (5 g of the hydrazone) reaction in which the product was obtained after recrystallization in 93% yield and 99% ee. Evidence for a stepwise mechanism and a model for the asymmetric induction are presented, as well. 相似文献
47.
K. Nishiyama K. Ishida K. Nagamine T. Matsuzaki Y. Kuno H. Shirakawa R. Kiefl J. H. Brewer 《Hyperfine Interactions》1986,32(1-4):551-556
The state of the muon in cis-polyacetylene was studied by muon spin rotation method under high transverse magnetic field.
The most of the muons are found to be in muonium substituted radical state. The hyperfine coupling constant was determined
to be 91 MHz with a line width of 10 MHz. 相似文献
48.
Shirakawa E Itoh K Higashino T Hayashi T 《Journal of the American Chemical Society》2010,132(44):15537-15539
Sodium tert-butoxide mediates the coupling of aryl halides with benzene derivatives without the aid of transition metal catalysts but with a catalytic 1,10-phenanthroline derivative. 相似文献
49.
Prof. Dr. K. Mizoguchi Dr. K. Shirakawa 《Archive of Applied Mechanics (Ingenieur Archiv)》1980,49(2):107-117
Summary The analytical method is presented for a cylindrical shell with spiral groove. The governing equations of cylindrical shell
derived by one of the authors are introduced and Kirchhoff's boundary conditions along any smooth path are deduced from the
principle of energy. The analysis is carried out for a cylindrical shell under a uniform bending moment by considering the
equilibrium conditions of a shell element. Numerical results are given for various geometrical parameters of cylindrical shell
and the angle of the spiral groove, some of which are confirmed by an experiment.
übersicht Die analytische Methode wird für eine Kreiszylinderschale mit spiraler Fuge entwickelt. Die von einem der Verfasser eingeführten Differentialgleichungen der Kreiszylinderschale und die Kirchhoffschen Randbedingungen l?ngs des beliebig geneigten Randes, die vom Prinzip der Energie hergeleitet wurden, werden angegeben. Das Problem der Kreiszylinderschale mit spiraler Fuge unter einem uniformen Biegemoment wird unter Berücksichtigung der komplizierten Gleichgewichtsbedingungen der Schalenelemente analysiert. Die numerischen Ergebnisse zeigen gute übereinstimmung mit experimentellen Ergebnissen.相似文献
50.
It has been experimentally shown that an O(-c)-polar ZnO surface is more stable than a Zn(+c)-polar surface in H(2) ambient. We applied first-principles calculations to investigating the polarity dependence on the stability at the electronic level. The calculations revealed that the -c surface terminated with H atom was stable maintaining a wurtzite structure, whereas the +c surface was unstable due to the change of coordination numbers of Zn at the topmost surface from four (wurtzite) to six (rock salt). This causes the generation of O(2) molecules, resulting in instability at the +c surface. 相似文献