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71.
Dr. Daisuke Uraguchi Fumito Ueoka Dr. Naoya Tanaka Dr. Tomohito Kizu Wakana Takahashi Prof. Dr. Takashi Ooi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(28):11553-11558
Catalysis by chiral weakly-coordinating anions (WCAs) remains underdeveloped due to the lack of a molecular design strategy for exploiting their characteristics, such as the non-nucleophilic nature. Here, we report the development of a chiral borate ion comprising an O,N,N,O-tetradentate backbone, which ensures hitherto unattainable structural robustness. Upon pairing with a proton, the hydrogen borate acts as an effective catalyst for the asymmetric Prins-type cyclization of vinyl ethers, providing access to structurally and stereochemically defined dihydropyrans. The key to selectivity control is the distinct ability of the borate ion to discriminate the prochiral faces of the acyclic oxonium ion intermediate and dictate the regiochemical outcome. We anticipate that this study paves the way for exploring the untapped potential of WCA catalysis for selective chemical synthesis. 相似文献
72.
Tomohito Tanaka Taishi Fujishiro Genichi Shigesato Shun‐ichi Hayashi 《Surface and interface analysis : SIA》2014,46(5):297-300
Ga‐focused ion beam time‐of‐flight secondary ion mass spectrometry (FIB‐TOF‐SIMS) analysis was performed to investigate the grain boundary segregation/precipitation of boron in steel. To overcome the low secondary ion yield from the primary Ga+ source and the sensitivity using a high‐resolution Ga‐FIB source, a low energy oxygen ion beam was used prior to the Ga‐FIB‐TOF‐SIMS analysis. As a result, it was found that Ga‐FIB‐TOF‐SIMS is a very powerful tool for mapping boron segregation and/or precipitation in steel with a spatial resolution of ~200 nm. In addition, the results were strongly dependent on the surface composition. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
73.
A photoreaction between benzoyl compounds, such as benzoylformate derivatives, and 2-(p-anisyl)-1,3-dimethylbenzimidazoline in the presence of allyl bromide was found to give various allylated alcohols. In the reaction of benzoylformates, α-hydroxy ester enolates, for which the negative charge occurs on the carbonyl carbon of benzoyl (umpolung reactivity), are proposed to be generated as intermediates by electron-transfer from benzimidazolines to the photoexcited benzoylformates; these species react with allyl bromide to produce α-allyl-α-hydroxy esters. 相似文献
74.
Tomohito Morosaki Tsubasa Suzuki Dr. Wei‐Wei Wang Prof. Shigeru Nagase Prof. Takayoshi Fujii 《Angewandte Chemie (International ed. in English)》2014,53(36):9569-9571
Electronic effects on the central carbon atom of carbone, generated by the replacement of the SIV ligand of carbodisulfane (CDS) with other chalcogen ligands (Ph2E, E=S or Se), were investigated. The carbones Ph2E→C←SPh2(NMe) [E=S( 1 ) or Se( 2 )] were synthesized from the corresponding salts, and their molecular structures and electronic properties were characterized. The carbone 2 is the first carbone containing selenium as the coordinated atom. DFT calculations revealed the electronic structures of 1 and 2 , which have two lone pairs of electrons at the carbon center. The trend in HOMO energy levels, estimated by cyclic voltammetry measurements, for the carbones and CDS follows the order of 2 > 1 >CDS. Analysis of a doubly protonated dication and trication complex revealed that the central carbon atom of 2 behaves as a four‐electron donor. 相似文献
75.
Tomohito Ogura Tomoya Higashihara Mitsuru Ueda 《Journal of polymer science. Part A, Polymer chemistry》2010,48(6):1317-1323
A negative‐type photosensitive polyimide (PSPI) based on semialicyclic poly(amic acid) (PAA), poly(trans‐1,4‐cyclohexylenediphenylene amic acid), and {[(4,5‐dimethoxy‐2‐nitrobenzyl)oxy]carbonyl} 2,6‐dimethylpiperidine (DNCDP) as a photobase generator has been developed as a next‐generation buffer coat material. The semialicyclic PAA was synthesized from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride and trans‐1,4‐cyclohexyldiamine in the presence of acetic acid, and the PAA polymerization solution was directly used for PSPI formulation. This PSPI, consisting of PAA (80 wt %) and DNCDP (20 wt %), showed high sensitivity of 70 mJ/cm2 and high contrast of 10.3, when it was exposed to a 365‐nm line (i‐line), postexposure baked at 190 °C for 5 min, and developed with 2.38 wt % tetramethylammonium hydroxide aqueous solution containing 20 wt % isopropanol at 25 °C. A clear negative image of 6‐μm line and space pattern was printed on a film, which was exposed to 500 mJ/cm2 of i‐line by a contact printing mode and fully converted to poly(trans‐1,4‐cyclohexylenebiphenylene imide) pattern upon heating at 250 °C for 1 h. The PSPI film had a low coefficient of thermal expansion of 16 ppm/K compared to typical PIs, such as prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride and 4,4′‐oxydianiline. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1317–1323, 2010 相似文献
76.
Akiyama E Kashimoto A Hotta H Kitsuki T 《Journal of colloid and interface science》2006,300(1):141-148
A new O/W (oil-in-water) emulsification system was developed using the amphiphilic polymer HHM-HEC (hydrophobically-hydrophilically modified hydroxyethylcellulose) and a lipophilic surfactant. HHM-HEC was used as a thickener and polymeric surfactant, and the addition of small quantities of various types of nonionic lipophilic surfactant (hydrophilic-lipophilic balance <5) decreased the droplet size of several types of oil due to a lowering of the tension at the water/oil interface. The oil droplets were held by the strong network structure of the aqueous HHM-HEC solution, preserving the O/W phase without inversion. These stable O/W emulsions were prepared without the addition of hydrophilic surfactants and thus show improved water repellency. 相似文献
77.
[Structure: see text] A powerful Ti-crossed Claisen condensation between ketene silyl acetals (KSAs) and acid chlorides was successfully performed to give alpha-monoalkylated esters and thermodynamically unfavorable (less accessible) alpha,alpha-dialkylated beta-keto esters in good yield (46 examples; 41-98% yield). A closely related reaction between ketene silyl thioacetals (KSTAs) and acid chlorides also proceeded smoothly to give alpha-monoalkylated and alpha,alpha-dialkylated beta-keto thioesters (21 examples; 61-97% yield). The present protocol was extended to the direct condensation of KSAs with carboxylic acids (14 examples; 71-97% yield). 相似文献
78.
Kye-Sung Park Wakao Sato Guido Grause Tomohito Kameda Toshiaki Yoshioka 《Thermochimica Acta》2009,493(1-2):105-108
Indium (In) was recovered from indium oxide (In2O3) and liquid crystal display (LCD) powder via a chloride volatilization process using polyvinyl chloride (PVC) as the chlorination agent. The recovery of In from In2O3 increased with an increasing molar Cl/In ratio in N2 and air atmospheres. The degree of In recovery at a Cl/In molar ratio of 11 and a temperature of 350 °C was 98.7% and 96.6%, for N2 and air, respectively. The In recovery also increased notably with increasing temperature in N2 atmosphere. In both atmospheres, the In recovery increased with an increasing degradation temperature of PVC. However, the In recovery from LCD powder was lower than that from In2O3. For LCD powder, the degree of In recovery at a Cl/In molar ratio of 11 and a temperature of 350 °C was 66.7% and 54.1%, for N2 and air, respectively. 相似文献
79.
Nakatsuji S Machida Y Maeno Y Tayama T Sakakibara T Duijn Jv Balicas L Millican JN Macaluso RT Chan JY 《Physical review letters》2006,96(8):087204
Strongly frustrated magnetism of the metallic pyrochlore oxide Pr2Ir2O7 has been revealed by single crystal study. While Pr 4f moments have an antiferromagnetic RKKY interaction energy scale of /T*/ = 20 K mediated by Ir 5d-conduction electrons, no magnetic long-range order is found except for partial spin freezing at 120 mK. Instead, the Kondo effect, including a lnT dependence in the resistivity, emerges and leads to a partial screening of the moments below /T*/. Our results indicate that the underscreened moments show spin-liquid behavior below a renormalized correlation scale of 1.7 K. 相似文献
80.
In a planar lens made of left-handed material (LHM), the rays converge to a focal point in the material and once again in
free space. The problems exhibited by the planar lens are its great thickness, the long optical path length, and energy concentration
in the LHM. We examine a bowl-shaped LHM lens with an index n = −1. In this lens, the back is a concave hemispherical surface and the rays never converge in the LHM, but in free space
only. We also designed a quantized bowl-shaped LHM lens composed of multiple layers of thin LHM plates of uniform thickness.
A bowl-shaped LHM lens quantized with more than 4 bits has a lens function similar to that of a smooth curved lens. The bowl-shaped
lens is characterized by its thinness, its short optical path length, and the absence of energy concentration in the LHM.
Furthermore, the quantized bowl-shaped LHM lens can be fabricated. Wave propagation through these lenses is numerically simulated
using the finite difference time domain (FDTD) method. 相似文献