排序方式: 共有94条查询结果,搜索用时 406 毫秒
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Kawabata T Kato M Mizugaki T Ebitani K Kaneda K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,11(1):288-297
Montmorillonite-enwrapped copper and scandium catalysts (Cu(2+)- and Sc(3+)-monts) were easily prepared by treating Na(+)-mont with the aqueous solution of the copper nitrate and scandium triflate, respectively. The resulting Cu(2+)- and Sc(3+)-monts showed outstanding catalytic activities for a variety of carbon-carbon bond-forming reactions, such as the Michael reaction, the Sakurai-Hosomi allylation, and the Diels-Alder reaction, under solvent-free or aqueous conditions. The remarkable activity of the mont catalysts is attributable to the negatively charged silicate layers that are capable of stabilizing metal cations. Furthermore, these catalysts were reusable without any appreciable loss in activity and selectivity. The Cu(2+)-mont-catalyzed Michael reaction proceeds via a ternary complex in which both the 1,3-dicarbonyl compound and the enone are coordinated to a Lewis acid Cu(2+) center. 相似文献
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The direct C-H substitution reactions of anilides using hypervalent iodine proceeded to afford azide, chloro, bromo, and fluoro derivatives, and their regioselectivity were described. In the specific reaction conditions, the unique regioisomers were obtained. 相似文献
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Dr. Robert J. Harris Kohki Nakafuku Dr. Alethea N. Duncan Robert G. Carden Dr. Jacob C. Timmerman Prof. Dr. Ross A. Widenhoefer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(40):10377-10386
The mechanism of the intermolecular hydroamination of 3-methylbuta-1,2-diene ( 1 ) with N-methylaniline ( 2 ) catalyzed by (IPr)AuOTf has been studied by employing a combination of kinetic analysis, deuterium labelling studies, and in situ spectral analysis of catalytically active mixtures. The results of these and additional experiments are consistent with a mechanism for hydroamination involving reversible, endergonic displacement of N-methylaniline from [(IPr)Au(NHMePh)]+ ( 4 ) by allene to form the cationic gold π-C1,C2-allene complex [(IPr)Au(η2-H2C=C=CMe2)]+ ( I ), which is in rapid, endergonic equilibrium with the regioisomeric π-C2,C3-allene complex [(IPr)Au(η2-Me2C=C=CH2)]+ ( I′ ). Rapid and reversible outer-sphere addition of 2 to the terminal allene carbon atom of I′ to form gold vinyl complex (IPr)Au[C(=CH2)CMe2NMePh] ( II ) is superimposed on the slower addition of 2 to the terminal allene carbon atom of I to form gold vinyl complex (IPr)Au[C(=CMe2)CH2NMePh] ( III ). Selective protodeauration of III releases N-methyl-N-(3-methylbut-2-en-1-yl)aniline ( 3 a ) with regeneration of 4 . At high conversion, gold vinyl complex II is competitively trapped by an (IPr)Au+ fragment to form the cationic bis(gold) vinyl complex {[(IPr)Au]2[C(=CH2)CMe2NMePh]}+ ( 6 ). 相似文献
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Two cyclic peptides, PF1171F (1) and PF1171G (2), were isolated from okara fermented with the unidentified ascomycete OK-128, and their structures were determined by NMR, MS, and Marfey amino acid analysis. Both peptides showed paralytic activity against silkworms. 相似文献
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Uchiyama S Kimura K Gota C Okabe K Kawamoto K Inada N Yoshihara T Tobita S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(31):9552-9563
An environment-sensitive fluorophore can change its maximum emission wavelength (λ(em)), fluorescence quantum yield (Φ(f)), and fluorescence lifetime in response to the surrounding environment. We have developed two new intramolecular charge-transfer-type environment-sensitive fluorophores, DBThD-IA and DBSeD-IA, in which the oxygen atom of a well-established 2,1,3-benzoxadiazole environment-sensitive fluorophore, DBD-IA, has been replaced by a sulfur and selenium atom, respectively. DBThD-IA is highly fluorescent in n-hexane (Φ(f) =0.81, λ(em) =537?nm) with excitation at 449?nm, but is almost nonfluorescent in water (Φ(f) =0.037, λ(em) =616?nm), similarly to DBD-IA (Φ(f) =0.91, λ(em) =520?nm in n-hexane; Φ(f) =0.027, λ(em) =616?nm in water). A similar variation in fluorescence properties was also observed for DBSeD-IA (Φ(f) =0.24, λ(em) =591?nm in n-hexane; Φ(f) =0.0046, λ(em) =672?nm in water). An intensive study of the solvent effects on the fluorescence properties of these fluorophores revealed that both the polarity of the environment and hydrogen bonding with solvent molecules accelerate the nonradiative relaxation of the excited fluorophores. Time-resolved optoacoustic and phosphorescence measurements clarified that both intersystem crossing and internal conversion are involved in the nonradiative relaxation processes of DBThD-IA and DBSeD-IA. In addition, DBThD-IA exhibits a 10-fold higher photostability in aqueous solution than the original fluorophore DBD-IA, which allowed us to create a new robust molecular nanogel thermometer for intracellular thermometry. 相似文献
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Fujikawa K Ganesh NV Tan YH Stine KJ Demchenko AV 《Chemical communications (Cambridge, England)》2011,47(38):10602-10604
Herein, we report the invention of a novel expeditious concept for oligosaccharide synthesis. Unlike the classic orthogonal strategy based on leaving groups, the reverse approach is based on orthogonal protecting groups, herein p-methoxybenzyl and 4-pentenoyl, which allows for efficient oligosaccharide assembly in the reverse direction. 相似文献
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Seisuke Nakashima Koji Sugioka Katsuhisa Tanaka Katsumi Midorikawa Kohki Mukai 《Applied physics. B, Lasers and optics》2013,113(3):451-456
Optical, magnetic, and magneto-optical properties have been investigated for the α-Fe2O3-doped transparent glasses irradiated with an infrared fs laser and subsequently annealed. The values of the saturation magnetization at room temperature for the irradiated glasses were increased compared with the as-prepared samples, which is due to the precipitation of the ferrimagnetic ferrite nanoparticles (NPs). By adding further dopants as precursors of plasmonic metals, Au or Al NPs were space-selectively precipitated together with the ferrite NPs in a confined region after irradiation and thermal annealing. In the case of the glass codoped with Al, magneto-optical Faraday effect was plasmonically enhanced and exhibited a negative distinct peak ascribed to a coupling between the ferrimagnetism of ferrite NPs and the localized surface plasmon resonance of Al NPs, while the glass, in which ferrite and Au NPs were precipitated, showed a positive enhancement of Faraday effect due to a coupling of plasmon resonance with diamagnetism of glass matrix. 相似文献
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