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901.
Tamura O Mitsuya T Huang X Tsutsumi Y Hattori S Ishibashi H 《The Journal of organic chemistry》2005,70(26):10720-10725
[reaction: see text] Intramolecular cycloaddition of novel 1,3-dipoles, N-boranonitrones, was examined. Treatment of O-tert-butyldimethylsilyloximes 9-12 having olefin moieties with 2 equiv of BF3 x OEt2 generated N-boranonitrones, which underwent intramolecular cycloaddition to afford N-nonsubstituted cycloadducts 16 (and/or 18) after extractive workup. Despite the Lewis-acidic conditions, the olefin geometry of the substrates was retained in the cycloadducts in the present cycloaddition. The electronic nature of the N-boranonitrones appeared to be electrophilic. In the case of substrate 11c, having an electron-donating methyl group at an internal position of the olefin moiety, the cycloaddition gave the bridged cycloadduct 18b. The cycloaddition proceeded at relatively low temperature, and the diastereoselectivity was high. 相似文献
902.
Yutaka Sawada Junji Yamaguchi Osamu Sakurai Keizo Uematsu Nobuyasu Mizutani Masanori Kato 《Thermochimica Acta》1979
Isothermal and non-isothermal decomposition of hydromagnesite 4 MgCO3 · Mg(OH)2 · 4 H2O was studied thermogravimetrically. Decarbonation was strongly influenced by the partial pressure of carbon dioxide. Decarbonation in an argon atmosphere proceeded via an amorphous lower carbonate to MgO. Decarbonation in a carbon dioxide atmosphere was interrupted at ~460–480°C. This interruption was explained by the formation of a metastable intermediate and the subsequent crystallization of MgCO3, both from the amorphous lower carbonate. This explanation was supported by DTA and power X-ray diffraction analysis of the quenched specimens. 相似文献
903.
Osamu Tamura Naka Mita Yasuharu Imai Takuya Nishimura Tamiko Kiyotani Mikio Yamasaki Motoo Shiro Nobuyoshi Morita Iwao Okamoto Tetsuya Takeya Hiroyuki Ishibashi Masanori Sakamoto 《Tetrahedron》2006,62(52):12227-12236
Uncatalyzed cycloaddition of α-alkoxycarbonylnitrones 1 with vinyl ethers 7 gave mixtures of cis- and trans-cycloadducts 8, whereas Eu(fod)3-catalyzed cycloaddition of 1 with 7 gave the trans-cycloadducts trans-8 in a highly stereoselective manner. NMR studies indicated that Eu(fod)3 selectively activated (Z)-nitrones (Z)-1 in E,Z-equilibrium mixtures of nitrones 1. In contrast, the reaction of 1 with allyl alcohols 12 in the presence of Eu(fod)3 resulted in sequential transesterification and intramolecular cycloaddition to give intramolecular cycloadducts 13. 相似文献
904.
Inaba T Tahara S Nisikawa N Kashiwagi H Sato F 《Journal of computational chemistry》2005,26(10):987-993
An all-electron density functional (DF) calculation on insulin was performed by the Gaussian-based DF program, ProteinDF. Quasi-canonical localized orbitals (QCLOs) were used to improve the initial guess for the self-consistent field (SCF) calculation. All calculations were carried out by parallel computing on eight processors of an Itanium2 cluster (SGI Altix3700) with a theoretical peak performance of 41.6 GFlops. It took 35 h for the whole calculation. Insulin is a protein hormone consisting of two peptide chains linked by three disulfide bonds. The numbers of residues, atoms, electrons, orbitals, and auxiliary functions are 51, 790, 3078, 4439, and 8060, respectively. An all-electron DF calculation on insulin was successfully carried out, starting from connected QCLOs. Regardless of a large molecule with complicated topology, the differences in the total energy and the Mulliken atomic charge between initial and converged wavefunctions were very small. The calculation proceeded smoothly without any trial and error, suggesting that this is a promising method to obtain SCF convergence on large molecules such as proteins. 相似文献
905.
The S1S0 non-adiabtic coupling constants were calculated for the disrotatory and conrotatory paths of the isomerization reaction between butadiene and cyclobutene. The calculated non-adiabatic coupling terms showed clearly the difference between the non-adiabatic interactions of the two reaction processes, and they correlate well with the Woodward-Hoffman rule. 相似文献
906.
A new photoresponsive crown ether (2) in which the poly)oxyethylene) chain is linked to 4? and 4′-position of azobenzene was synthesized. Trans-(2) completely lacked the affinity to alkali metal cations, while photoisomerized cis-(2) was capable of binding K+, Rb+, and Cs+. 相似文献
907.
Sandanayaka AS Zhang H Takaguchi Y Sako Y Tamura M Araki Y Ito O 《Chemical communications (Cambridge, England)》2005,(41):5160-5162
Photoinduced charge separation of fullerodendrimers with carboxylates at terminal sites (C60 approximately COO-) has been found in aqueous media. Time-resolved transient absorption and fluorescence measurements of the fullerodendrimers demonstrated that charge separation takes place from the terminal carboxylate anion to the central excited singlet state of C60, generating C60*- approximately COO* with high quantum efficiency in aqueous solution. In the presence of viologen dication and a sacrificial donor, the persistent viologen radical cation was generated. 相似文献
908.
Seiji Shinkai Hisatake Hamada Akihiko Dohyama Osamu Manabe 《Tetrahedron letters》1980,21(17):1661-1664
Protonated α-imino acids, RC(=NH2+)COOH, were easily reduced to α-amino acids by an acid-stable NADH analogue, 1-benzyl-3-carbamoyl-1,4-dihydroquinoline. This is the first model reaction of NADH-mediated α-amino acid synthesis from α-keto acids. 相似文献
909.
Dr.Sc. Shoichi Igarashi Osamu Yamamoto Hirotaro Kambe 《Colloid and polymer science》1964,199(2):97-104
Summary The changes of crystalline and amorphous phases in a linear polyethylene by thermal oxidation were studied by differential thermal and infrared analyses. In the differential thermal analysis curve for polyethylene in a stream of oxygen an exothermic peak was obtained in the 180 °C region. It was confirmed by infrared method that the exothermic peak is due to oxidation of vinyl type double bond in the polymer molecule. This oxidation caused to decrease the crystallinity of polyethylene.The differential thermal and infrared analyses of polyethylenes oxidized in the solid state are compared with the above results. Further, it was observed that the differential thermal analyses for crystallization of unoxidized and oxidized polyethylenes show two peaks depending on the condition of melt annealing of the samples.
Zusammenfassung Die Änderungen der kristallinen und amorphen Phasen in einem linearen Polyäthylen bei thermischer Oxydation wurden mit Thermodifferentialanalyse, mit Infrarot untersucht. In der DTA-Kurve für Polyäthylen in einem Strom von Sauerstoff wurde ein exothermer Pik bei etwa 180 °C erhalten. Es wurde durch Infrarot festgestellt, daß dies einer Oxydation von Vinyldoppelbindungen im Polymermolekül entspricht. Diese Oxydation verursacht die Verminderung der Kristallinität des Polyäthylens.Die differential-thermo-analytischen und Ultrarot-Werte von oxydiertem Polyäthylen in festem Zustand wurden mit den obigen Versuchen verglichen und so weiter beobachtet, daß die DTA-Kurven von unoxydierten und oxydierten Polyäthylenen 2 Piks zeigten, die von den Bedingungen der Schmelz-Temperung der Proben abhängen.相似文献
910.
2,2,2-Trifluoroethyldiphenylphosphine oxide [Ph2P(O)CH2CF3] (2) is known to give no Horner reaction product with enolizable aldehydes. We found, however, that some enolizable aldehydes such as N-Boc-pyrrolidine-2-aldehyde (9) gave the expected 3,3,3-trifluoroprop-1-enyl compounds by reaction with 2. The products could be further transformed to some 2,2,2-trifluoroethyl-substituted nitrogen-containing heterocycles by using radical cyclization or Heck reaction. 相似文献