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261.
Hayashi Y Shoji M Yamaguchi S Mukaiyama T Yamaguchi J Kakeya H Osada H 《Organic letters》2003,5(13):2287-2290
The asymmetric total syntheses of pseurotin A and 8-O-demethylpseurotin A have been accomplished. Key reactions are a NaH-promoted intramolecular cyclization of an alkynylamide to form a gamma-lactam, an aldol reaction of a benzylidene-substituted ketone, and the late-stage introduction of the benzoyl group by a selective oxidation of a benzylidene moiety with dimethyldioxirane (DMD). [reaction: see text] 相似文献
262.
Tridentate PSiP pincer-type palladium complex-catalyzed hydrocarboxylation of allenes under carbon dioxide to give synthetically useful beta,gamma-unsaturated carboxylic acids was developed. This novel CO2-fixation reaction is thought to proceed through the catalytic generation of sigma-allyl palladium species via hydropalladation of allenes, followed by its regioselective nucleophilic addition to CO2 in the presence of an appropriate reducing agent. The reaction is successfully applied to various allenes bearing functional groups such as ester, carbamate, ketone, and alkene, showing high synthetic utility of this protocol. 相似文献
263.
We have developed a fundamentally new type of simple lattice Boltzmann (LB) model for the compressible Navier-Stokes equations based on the kinetic system proposed by Sone. The model uses the kinetic equation of free-molecular type in the streaming process and modifies the distribution function to its Chapman-Enskog type at each time step. Compared with the current LB models, the proposed model is superior in the following two points: (i) there are no inherent errors associated with the Knudsen number; (ii) any flow parameters, including three transport coefficients, can be chosen freely according to our convenience. Numerical tests and error estimates confirm the above statements. 相似文献
264.
Tatsuyoshi Ito Prof. Dr. Nobuharu Iwasawa Dr. Jun Takaya 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(29):12011-12015
An unprecedented photo-promoted skeletal rearrangement reaction of phosphine–borane frustrated Lewis pairs, o-(borylaryl)phosphines, involving cleavage of an unstrained sp2C–sp3C σ-bond is reported. The reaction realizes an efficient synthesis of cyclic phosphonium borate compounds. The reaction mechanism via a boranorcaradiene intermediate is proposed based on theoretical calculations. This work sheds light on the new photoreactivity of phosphine–borane FLPs. 相似文献
265.
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267.
Marc Steinmetz Kirika Ueda Prof. Dr. Stefan Grimme Dr. Junichiro Yamaguchi Dr. Sylvia Kirchberg Prof. Dr. Kenichiro Itami Prof. Dr. Armido Studer 《化学:亚洲杂志》2012,7(6):1256-1260
Direct C? H phenylation of 2‐ethylthiophene and 2‐chlorothiophene with PhPdI(bipy) complex to form either the corresponding 4‐phenyl or 5‐phenylthiophene derivative is studied under stoichiometric conditions using various Lewis acids as additives. It is shown that reactions occur via the corresponding cationic Pd complex (PhPdbipy+) and that the counteranion determines the regioselectivity. High‐level DFT calculations reveal that C? C bond formation occurs via a carbopalladation pathway and not via electrophilic palladation. These calculations give some indications regarding the regioselectivity of the thiophene arylation. 相似文献
268.
Iwamoto T Okita J Kabuto C Kira M 《Journal of the American Chemical Society》2002,124(39):11604-11605
The proton abstraction (sila-metalation) of trialkylsilyl-substituted dihydridosilanes with t-BuLi or LDA in THF was found to be a convenient route to the corresponding silyllithiums (RR'SiHLi; 1a, R, R' = t-BuMe(2)Si; 1b, R, R' = Me(3)Si; 1c, R, R' = i-Pr(2)MeSi; 1d, R = t-BuMe(2)Si, R' = 4-methylphenyl). Hydridosilylithium 1a was isolated as air- and moisture-sensitive, but thermally stable, colorless crystals. X-ray analysis has shown that 1a is dimeric in the solid state, where two lithium atoms bridge between anionic silicon atoms forming a parallelogram, each lithium atom is coordinated by one THF molecule, and the Si-H hydrogen atoms are in the plane of the parallelogram. X-ray analysis has shown that (t-BuMe(2)Si)(2)GeHLi (5) has a dimeric structure similar to that of 1a. 相似文献
269.
Nohta H Sonoda J Yoshida H Satozono H Ishida J Yamaguchi M 《Journal of chromatography. A》2003,1010(1):37-44
A highly sensitive and selective fluorimetric determination method for dicarboxylic acids (C5-C12) has been developed. This method is based on an intramolecular excimer-forming fluorescence derivatization with a pyrene reagent, 4-(1-pyrene)butyric acid hydrazide (PBH), followed by reversed-phase liquid chromatography (LC). The carboxylic acids were converted to the corresponding dipyrene-labeled derivatives by reaction with PBH in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. The derivatives afforded intramolecular excimer fluorescence (450-550 nm) which can clearly be discriminated from the normal fluorescence (370-420 nm) emitted from PBH and monopyrene-labeled derivatives of monocarboxylic acids. The structures of the derivatives and the emission of excimer fluorescence were studied by LC with mass spectrometry and with spectrofluorimetry, respectively. The PBH derivatives of the carboxylic acids could be separated by reversed-phase LC on an ODS column with isocratic elution. The detection limits (signal-to-noise ratio = 3) were 1.3 fmol to undetectable for a 20-microl injection. 相似文献
270.
Aleksandar Staykov Junichiro Yamabe Brian P. Somerday 《International journal of quantum chemistry》2014,114(10):626-635
A small addition of oxygen to hydrogen gas is known to mitigate the hydrogen embrittlement (HE) of steels. As atomic hydrogen dissolution in steels is responsible for embrittlement, catalysis of molecular hydrogen dissociation by the steel surface is an essential step in the embrittlement process. The most probable role of oxygen in mitigating HE is to inhibit the reactions between molecular hydrogen and the steel surface. To elucidate the mechanism of such surface reaction of hydrogen with the steel in the presence of oxygen, hydrogen, and oxygen adsorption, dissociation, and coadsorption on the Fe(100) surface were investigated using density functional theory. The results show that traces of O2 would successfully compete with H2 for surface adsorption sites due to the grater attractive force acting on the O2 molecule compared to H2. The H2 dissociation would be hindered on iron surfaces with predissociated oxygen. Prompted by the notable results for H2 + O2, other practical systems were considered, that is, H2 + CO and CH4. Calculations were performed for the CO chemisorption and H2 dissociation on iron surface with predissociated CO, as well as, CH4 surface dissociation. The results indicate that CO inhibition of H2 dissociation proceeds via similar mechanism to O2 induced inhibition, whereas CH4 traces in the H2 gas have no effect on H2 dissociation. © 2014 Wiley Periodicals, Inc. 相似文献