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951.
PyBidine–Cu(OTf)2‐Catalyzed Asymmetric [3+2] Cycloaddition with Imino Esters: Harmony of Cu–Lewis Acid and Imidazolidine‐NH Hydrogen Bonding in Concerto Catalysis
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Prof. Dr. Takayoshi Arai Hiroki Ogawa Dr. Atsuko Awata Dr. Makoto Sato Megumi Watabe Prof. Dr. Masahiro Yamanaka 《Angewandte Chemie (International ed. in English)》2015,54(5):1595-1599
A bis(imidazolidine)pyridine (PyBidine)–Cu(OTf)2 complex catalyzing the endo‐selective [3+2] cycloaddition of nitroalkenes with imino esters was applied to the reaction of methyleneindolinones with imino esters to afford spiro[pyrrolidin‐3,3′‐oxindole]s in up to 98 % ee. X‐ray crystallographic analysis of the PyBidine–Cu(OTf)2 complex and DFT calculations suggested that an intermediate Cu enolate of the imino ester reacts with nitroalkenes or methyleneindolinones, which are activated by NH‐hydrogen bonding with the PyBidine–Cu(OTf)2 catalyst. 相似文献
952.
Keiji Yoshimura Ryoei Kikuchi Takashi Kimoto Toru Ozeki Kazuhiko Imano Masahiro Kajikawa Nobuaki Ogawa 《Analytical sciences》2006,22(6):845-848
Fog droplets in the atmosphere are first produced by the activation of cloud condensation nuclei (CCN), which are originally some ionic compound. Subsequently, the nuclei grow by vapor diffusion. Fog droplets are polluted through the activation process and successive diffusion growth and residence (post activation). We cannot distinguish the effects of the two pollution processes of natural fog water samples. We found that fog droplets can be produced artificially without CCN using an ultrasonic humidifier. Because the artificial fog droplets are not polluted by CCN, the movement of the fog droplets in natural air will take up some pollutants in the air. Consequently, the two pollution processes of fog (the activation of CCN and the post activation process) can be discriminated using data from field experiments. This sampling analytical method is extremely important for further research regarding fog, clouds and environmental chemistry. 相似文献
953.
The extraction behaviors of bismuth(III) with carboxylic acid (HL), which have not yet been clearly elucidated, because of the precipitation of hydroxide, were studied using the 2-bromoalkanoic acid in benzene and in hexane systems under aqueous conditions of high acidity at I = 1.0 M ((H,Li)NO3). The extraction equilibria were analyzed based on the-initial concentration of nitric acid and the concentration of bismuth(III) extracted in the organic phase. The extracted species and the logarithmic values of the extraction constant (log Kex) were found to be a single species of BiL3(HL)3 for the systems of 2-bromooctanoic acid/benzene (log Kex = -1.66) and 2-bromohexadecanoic acid/benzene (-1.58), and to be two species of BiL3(HL)4 (-1.01) and Bi3L9HL (-1.62) for the system of 2-bromooctanoic acid/hexane, where the monomer was dominant at a higher reagent concentration. 相似文献
954.
The hydrogen content in a-Si1−xGex:H thin films is an important factor deciding the density and the optical band gap. We measured the elemental depth profiles of hydrogen together with Si and Ge by elastic recoil detection analysis (ERDA) combined with Rutherford backscattering (RBS) using MeV He2+ ions. In order to determine the hydrogen depth profiles precisely, the energy- and angle-dependent recoil cross-sections were measured in advance for the standard sample of a CH3+-implanted Si substrate. The cross-sections obtained here are reproduced well by a simple expression based on the partial wave analysis assuming a square well potential (width: r0 = 2.67 × 10−13 cm, depth: V0 = −36.9 MeV) within 1%. For the a-Si1−xGex:H films whose elemental compositions were determined by ERDA/RBS, we measured the secondary ions yields of HCs2+, SiCs2+, H−, Si− and Ge− as a function of Ge concentration x. As a result, it is found that the useful yield ratios of HCs2+/SiCs2+, H−/Si− and Ge−/Si− are almost constant and thus the elemental depth profiles of the a-Si1−xGex:H films can be also determined by secondary ion mass spectrometry (SIMS) within 10% free from a matrix effect. 相似文献
955.
In the field of materials science, π-conjugated molecules bearing a group 16 heteroatom are of great importance. Sulfur or selenium containing porphyrins were successfully synthesized using the transition-metal-catalyzed reaction with diphenyl dichalcogenides. NMR studies indicated the preferential formation of the (Z)-isomer. 相似文献
956.
Received: 20 September 1998 相似文献
957.
Hideaki Ichiba Tomoko Ogawa Takehiko Yajima Takeshi Fukushima 《Biomedical chromatography : BMC》2009,23(10):1051-1058
Structural modification of a polypeptide hormone, glucagon, by a hydroxyl radical in vitro was investigated by reversed‐phase high‐performance liquid chromatography (RP‐HPLC), and the oxidized site of glucagon was detected by electrospray ionization tandem mass spectrometry (ESI‐MS/MS). It was shown that 27methionine (Met) was oxidized to 27Met sulfoxide by hydroxyl radical, and the production rate of 27Met sulfoxide was faster than that by hydrogen peroxide. In addition, production of 27Met sulfoxide enantiomer was confirmed by RP‐HPLC analysis. cAMP production in a HepG2 cell induced by 27Met sulfoxide glucagon was reduced to approximately 75% as compared with that induced by the native form of glucagon. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
958.
959.
Masao Ogawa 《Mathematische Annalen》2006,335(1):47-77
We consider the free boundary problem for an incompressible ideal fluid in the two-dimensional space. We show the unique existence
of the solution, locally in time, even if the initial surface and the bottom are uneven. 相似文献