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61.
Masaya Nakajima Sho Nagasawa Koki Matsumoto Takahito Kuribara Atsuya Muranaka Masanobu Uchiyama Tetsuhiro Nemoto 《Angewandte Chemie (International ed. in English)》2020,59(17):6847-6852
According to the Grotthuss–Draper law, light must be absorbed by a substrate to initiate a photoreaction. There have been several reports, however, on the promotion of photoreactions using hypervalent iodine during irradiation with light from a non‐absorbing region. This contradiction gave rise to a mystery regarding photoreactions involving hypervalent iodine. We demonstrated that the photoactivation of hypervalent iodine with light from the apparently non‐absorbing region proceeds via a direct S0→Tn transition, which has been considered a forbidden process. Spectroscopic, computational, and synthetic experimental results support this conclusion. Moreover, the photoactivation mode could be extended to monovalent iodine and bromine, as well as bismuth(III)‐containing molecules, providing new possibilities for studying photoreactions that involve heavy‐atom‐containing molecules. 相似文献
62.
Dr. Shingo Harada Koki Tanikawa Haruka Homma Chigaya Sakai Tsubasa Ito Prof. Dr. Tetsuhiro Nemoto 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(52):12058-12062
An enantioselective insertion reaction of silver carbenes generated from donor–acceptor-substituted diazo compounds into the O−H bond of phenols was developed. A homobinuclear silver complex with a chiral phosphorous ligand was created in situ from AgNTf2 and (S)-XylylBINAP (in a 2:1 mole ratio). Detailed mechanistic studies using combined experimental and computational techniques revealed that one silver atom center of the catalyst forms a silver carbene and another one works as a Lewis acid for the nucleophilic addition of a phenol. Two counter-anions, two water molecules, and two silver atoms cooperatively mediate the subsequent protonation event to lower the activation energy and control enantioselectivity, affording an array of valuable α-aryl-α-aryloxy esters. 相似文献
63.
D3h‐Symmetrical Shape‐Persistent Macrocycles Consisting of Pyridine–Acetylene–Phenol Conjugates as an Efficient Host Architecture for Saccharide Recognition
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Dr. Hajime Abe Tetsuhiro Yoneda Dr. Yuki Ohishi Prof. Dr. Masahiko Inouye 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(52):18944-18952
Hexagonal shape‐persistent macrocycles (SPMs) consisting of three pyridine and three phenol rings linked with acetylene bonds were developed as a preorganized host for saccharide recognition by push–pull‐type hydrogen bonding. Three tert‐butyl or 2,4,6‐triisopropylphenyl substituents were introduced on the host to suppress self‐aggregation by steric hindrance. In spite of the simple architecture, association constants Ka of the host with alkyl glycoside guests reached the order of 106 m ?1 on the basis of UV/Vis titration experiments. This glycoside recognition was much stronger than that in the cases of acyclic equivalent hosts because of the entropic advantage brought by preorganization of the hydrogen‐bonding sites. Solid–liquid extraction and liquid–liquid transport through a liquid membrane were demonstrated by using native saccharides, and much preference to mannose was observed. 相似文献
64.
Mariko Yoshida Tetsuhiro Nemoto Zengduo Zhao Yuta Ishige Yasumasa Hamada 《Tetrahedron: Asymmetry》2012,23(11-12):859-866
A novel catalytic asymmetric synthetic method for making spirocyclohexadienones with an all-carbon quaternary spirocenter was developed based on the Pd-catalyzed intramolecular ipso-Friedel–Crafts allylic alkylation of phenols. When 5 mol % of the Pd catalyst and 12 mol % of (?)-9-NapBN (?)-3e were used, the spirocyclic adduct was obtained with up to 93% ee, albeit with low chemical yield. On the other hand, when using 6 mol% of the Trost ligand (R,R)-3k, the spirocyclic adducts were obtained in good yields with up to 89% ee (diastereoselectivity = 9.2:1). 相似文献
65.
Yoshihiko Ooka Fumihiko Kanai Shinichiro Okabe Takuya Ueda Ryota Shimofusa Sadahisa Ogasawara Tetsuhiro Chiba Yasunori Sato Masaharu Yoshikawa Osamu Yokosuka 《Magnetic resonance imaging》2013
Purpose
To assess the value of gadoxetic acid-enhanced magnetic resonance imaging (MRI) for the pre-therapeutic detection of hepatocellular carcinoma (HCC) using receiver operating characteristic (ROC) analysis with the combination of computed tomography (CT) arterial portography and CT hepatic arteriography (CTAP/CTHA).Materials and Methods
A total of 54 consecutive patients with 87 nodular HCCs were retrospectively analyzed. All HCC nodules were confirmed pathologically. Three blinded readers independently reviewed 432 hepatic segments, including 78 segments with 87 HCCs. Each reader read two sets of images: Set 1, CTAP/CTHA; Set 2, gadoxetic acid-enhanced MRI including a gradient dual-echo sequence and diffusion-weighted imaging (DWI). The ROC method was used to analyze the results. The sensitivity, specificity, positive predictive value, negative predictive value and sensitivity according to tumor size were evaluated.Results
For each reader, the area under the curve was significantly higher for Set 2 than for Set 1. The mean area under the curve was also significantly greater for Set 2 than for Set 1 (area under the curve, 0.98 vs. 0.93; P = .0009). The sensitivity was significantly higher for Set 2 than for Set 1 for all three readers (P = .012, .013 and .039, respectively). The difference in the specificity, positive predictive values and negative predictive values of the two modalities for each reader was not significant (P > .05).Conclusion
Gadoxetic acid-enhanced MRI including a gradient dual-echo sequence and DWI is recommended for the pre-therapeutic evaluation of patients with HCC. 相似文献66.
Tetsuhiro Nemoto 《Tetrahedron letters》2006,47(26):4365-4368
We developed an efficient method for the synthesis of 3-substituted 2,3-dihydroquinolin-4-ones using a one-pot sequential multi-catalytic process: Pd-catalyzed allylic amination-thiazolium salt-catalyzed Stetter reaction cascade. Measurement of the initial rate of the developed sequential process revealed a significant increase in the reaction rate of the Stetter reaction in the presence of Pd(OAc)2 and AcOH·i-Pr2NEt, the constituents of the first Pd catalysis. 相似文献
67.
[reaction: see text] We have recently developed a new class of chiral phosphorus ligands: P-chirogenic diaminophosphine oxides. These pentavalent phosphorus compounds have been successfully applied to Pd-catalyzed asymmetric construction of tertiary and quaternary carbons. The actual ligand structure was the trivalent phosphorus species 17, which was generated in situ by BSA-induced P(V) to P(III) transformation of 6, the preligand. Detailed mechanistic studies, including asymmetric amplification and initial rate kinetics, revealed that complex 18 [Pd-17 (1:2) complex] was the active catalyst. The important function of the nitrogen atom on the sidearm in the ligands was also clarified. The source of enantioselection in the construction of asymmetric quaternary carbons was the secondary ligand substrate interaction mediated by N-Zn coordination. 相似文献
68.
Significantly different characteristics have been observed between Ge42S58 films prepared by thermal evaporation and bulk Ge42S58 glasses prepared by melt-quench. The film exhibits a higher electrical conductivity by about four orders of magnitude and contains a higher density of paramagnetic defect compared with the bulk. A large increase of the electrical conductivity is attained by doping with a small amount of Ag into the bulk, but the doping effect is hardly observed in the film. These differences are considered to result from larger topological disorder and larger defect density in the film network compared with the bulk network. 相似文献
69.
Yoshiyuki Inaguma Tetsuhiro KatsumataMitsuru Itoh Yukio Morii 《Journal of solid state chemistry》2002,166(1):67-72
The crystal structure of a lithium ion-conducting perovskite La0.62(2)Li0.16(1)TiO3.01(3) obtained by furnace-cooling was refined by the Rietveld method using neutron-diffraction data at room temperature and 77 K. The adopted space group was Cmmm (No. 65). The anti-phased tilts of TiO6 octahedra along the b-axis in addition to alternative arrangement of La ions along the c-axis was confirmed. The position of Li was refined to be off-centered and in two equivalent positions in an A-site. The obtained structural information implies that the lithium ion conduction among A-sites occurs in the vicinity of La-poor layers two-dimensionally rather than three-dimensionally in this compound. 相似文献
70.
Nemoto T Matsumoto T Masuda T Hitomi T Hatano K Hamada Y 《Journal of the American Chemical Society》2004,126(12):3690-3691
We successfully synthesized a novel P-chirogenic diaminophosphine oxide 4, which was applied to catalytic enantioselective construction of quaternary carbon centers using Pd-catalyzed asymmetric allylic substitution with various beta-keto esters (up to 99% yield, 94% ee). Preliminary mechanistic studies indicated that two molecules of 8 coordinate to the Pd metal in a monodentate fashion, resulting in the formation of Pd complex 9 (Pd:8 = 1:2), which functions as the active species. 相似文献