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261.
Shobu Hiraoka Tsutomu Matsumoto Koki Matsuzaka Takaaki Sato Noritaka Chida 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(13):4425-4429
An approach to cyclic nitrones from N‐hydroxylactam derivatives is documented. The nucleophilic addition of an organolithium reagent to an N‐OSEM [SEM=2‐(trimethylsilyl)ethoxymethyl] lactam forms a five‐membered chelated intermediate, which undergoes both elimination and deprotection to give a fully substituted nitrone in a one‐pot process. When combined with the N‐oxidation of easily available chiral lactams, this method becomes especially useful for the quick synthesis of chiral nitrones in enantio‐pure form, enabling the concise total synthesis of cylindricine C. 相似文献
262.
Koki Watanabe Kiyotoshi Yasumoto 《International Journal of Infrared and Millimeter Waves》1999,20(12):2163-2174
A coupled-mode formulation for an NRD-guide coupler is presented using the singular perturbation technique. The first-order and second-order perturbations are taken into account in the analysis and the coupled-mode equations based on the eigenmodes of each waveguide in isolation are derived. The propagation constants obtained by these equations are compared with those by the exact theory, conventional coupled-mode theory, and improved coupled-mode theory. The numerical results of present formulation are in good agreement with the exact theory and superior to those of the other formulations. 相似文献
263.
Haraguchi K Takahashi H Shiina N Horii C Yoshimura Y Nishikawa A Sasakura E Nakamura KT Tanaka H 《The Journal of organic chemistry》2002,67(17):5919-5927
Three types of 4-thiofuranoid glycal with different 3,5-O-silyl protecting groups were prepared and their electrophilic glycosidation was investigated. The 3,5-bis-O-(tert-butyldimethylsilyl)-4-thiofuranoid glycal (5) was obtained through mesylation of 2-deoxy-4-thio-D-erythro-pentofuranose (4) and subsequent base-promoted elimination, while thermal elimination of sulfoxide derivatives was suitable for the preparation of 3,5-O-(tetraisopropyldisiloxane-1,3-diyl) (9) and 3,5-O-(di-tert-butylsilylene) (11) 4-thioglycals. The glycosidation reactions of these 4-thioglycals were carried out, in the presence of either PhSeCl or NIS, by using silylated derivatives of uracil, thymine, cytosine, and N(6)-benzoyladenine. Among the three 4-thioglycals, 11 was found to be an excellent glycosyl donor, forming the desired beta-anomer exclusively irrespective of the nucleobase employed. 相似文献
264.
Gas chromatography of aromatic acids 总被引:1,自引:0,他引:1
265.
266.
Nuclear magnetic resonance (NMR) spectroscopy reveals that solution-grown polyethylene samples have a unique phase structure independent of molecular weight. The lamellar crystallites are composed of about 85% crystalline material with the noncrystalline overlayer as large as 15%. The molecular motion in the overlayer is comparatively hindered and the liquid-like component, which is generally recognized in melt-grown crystals, cannot be produced appreciably, even at 60°C. Such hindered molecular mobility can be understood in terms of a rather restricted conformation of the molecular chains in the noncrystalline overlayer, arising from the special mode of crystallization from dilute solution. 相似文献
267.
268.
Takenaka K Nakada K Osuka A Horii S Ikuta H Hirabayashi I Sugai S Mizutani U 《Physical review letters》2000,85(25):5428-5431
The optical spectra of PrBa2Cu4O8 show large in-plane anisotropy. For the a polarization (E perpendicular chain), the spectrum is characterized by a gap of 1.4 eV, indicating the charge-transfer insulating nature of the CuO2 planes. For the metallic chain direction (E // b), the spectrum deviates from a simple Drude response; reflectivity R(b)(omega) shows a sharp edge at approximately 1 eV but it also shows a dip at approximately 15 meV, which splits the conductivity spectrum into two parts--a zero-energy mode with small weight and a pronounced 40 meV mode. These features are discussed in terms of a Tomonaga-Luttinger liquid in a doped 1D Mott insulator and compared with 1D Bechgaard salts. 相似文献
269.
Yuui Yokota Jun-ichi Shimoyama Tetsuro Ogata Shigeru Horii Kohji Kishio 《Solid State Communications》2007,142(8):429-433
We have examined the effects of excess oxygen on the magnetization, electrical transport properties and crystal structure of La0.95Sr0.05MnOy. An antiferromagnetic insulator phase confirmed in the as-grown crystal at low temperatures changed to a ferromagnetic insulator phase after the introduction of excess oxygen. The ferromagnetic transition temperature, TC, systematically increased with increasing oxygen content, y, due to an increase in the mean valence of manganese. However, the TC of crystals with excess oxygen was lower than that of the La1−xSrxMnO3.00 having identical manganese valence. This is considered to be a result of the competition among the mean valence of manganese, the concentration of cation vacancies, and the mean ionic radius of cations at the A-site. 相似文献
270.
This article describes the formal synthesis of quebrachamine based on regio- and stereoselective hydrocyanation of 1,3-disubstituted allenes. Allenyl CC double bonds are effectively discriminated through Ni-catalyzed hydrocyanation and a CN group is utilized as a synthon of piperidine ring. Several steps from HCN adduct afforded known intermediates to quebrachamine. 相似文献