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排序方式: 共有729条查询结果,搜索用时 15 毫秒
721.
A facile method for the synthesis of 3-amino-5-(2-pyridyl)-1,4-benzodiazepin-2-ones (8) mediated by benzotriazole is described. The synthesis and optical resolution of the product by fractional crystallisation proceeds in high yield, under mild conditions and without recourse to toxic reagents or chromatographic separations and hence is amenable to the large scale preparation of these important precursors to potent CCK receptor ligands. 相似文献
722.
We have investigated the aggregate structures of a colloidal dispersion composed of ferromagnetic disk-like particles with
a magnetic moment normal to the particle axis at the particle center, by means of 3D Monte Carlo simulations. Such disk-like
particles have been modeled as a circular disk-like particle with the side section shape of spherocylinder. We have attempted
to clarify the influences of the magnetic field strength, magnetic interactions between particles and volumetric fraction
of particles. In order to discuss quantitatively the aggregate structures of clusters, we have focused on the radial distribution
and orientational pair correlation functions, etc. For no applied magnetic field cases, long column-like clusters come to
be formed with increasing magnetic particle–particle interactions. The internal structures of these clusters clearly show
that the particles incline in a certain direction and their magnetic moments alternate in direction between the neighboring
particles in the clusters. For applied magnetic field cases, the magnetic moment of each particle inclines in the magnetic
field direction and therefore the column-like clusters are not formed straightforwardly. If the magnetic field is much stronger
than magnetic particle–particle interactions, the particles do not have a tendency to form the clusters. As the influence
of magnetic particle–particle interactions is significantly strong, thick chain-like clusters or column-like clusters or brick-wall-like
clusters come to be formed along the magnetic field direction. 相似文献
723.
The straightforward synthesis of isochromene derivatives and related cyclic ethers is achieved by the rhodium-catalyzed oxidative coupling of α,α-disubstituted benzyl and allyl alcohols with alkynes. The hydroxy groups effectively act as the key function for the regioselective C-H bond cleavage. 相似文献
724.
The rhodium-catalyzed oxidative 1:2 coupling reactions of arylboronic acids or their esters with alkynes smoothly proceed to produce the corresponding annulated products. Of special note, highly substituted, readily soluble, and tractable anthracene and tetracene derivatives can be obtained selectively from 2-naphthyl- and 2-anthrylboron reagents, respectively. 相似文献
725.
Satoh H Manabe S Ito Y Lüthi HP Laino T Hutter J 《Journal of the American Chemical Society》2011,133(14):5610-5619
An endocyclic pathway is proposed as a reaction mechanism for the anomerization from the β (1,2-trans) to the α (1,2-cis) configuration observed in glycosides carrying 2,3-trans cyclic protecting groups. This reaction occurs in the presence of a weak Lewis or Br?nsted acid, while endocyclic cleavage (endocleavage) in typical glycosides was observed only when mediated by protic media or strong Lewis acids. To rationalize the behavior of this class of compounds, the reaction mechanism and the promoting factors of the endocleavage are investigated using quantum-mechanical (QM) calculations and experimental studies. We examine anomerization reactions of thioglycosides carrying 2,3-trans cyclic protecting groups, employing boron trifluoride etherate (BF(3)·OEt(2)) as a Lewis acid. The estimated theoretical reactivity, based on a simple model to predict transition state (TS) energies from the strain caused by the fused rings, is very close to the TS energies calculated by the TS search along the C1-C2 bond rotation after the endo C-O bond breaking. Excellent agreement is found between the predicted TS energies and the experimental reactivity ranking. The series of calculations and experiments strongly supports the predominance of the endocyclic rather than the exocyclic mechanism. Furthermore, these investigations suggest that the inner strain is the primary factor enhancing the endocleavage reaction. The effect of the cyclic protecting group in restricting the pyranoside ring to a (4)C(1) conformation, extensively discussed in conjunction with the stereoelectronic effect theory, is shown to be a secondary factor. 相似文献
726.
Kadono R Shimomura K Satoh KH Takeshita S Koda A Nishiyama K Akiba E Ayabe RM Kuba M Jensen CM 《Physical review letters》2008,100(2):026401
We have detected the occurrence of hydrogen bonding involving an interstitial positive muon situated between hydrogen atoms of two independent alanate anions in sodium alanate (NaAlH4). Ti doping, which is known to dramatically improve the hydrogen cycling performance of NaAlH4, reduces the kinetic barrier of the transition of the muon from the muon-dialanate state to a mobile interstitial state. This observation strongly suggests that hydrogen bonding is the primary bottleneck for hydrogen release or uptake in sodium alanate, which might be common to other complex hydrides. 相似文献
727.
Takekazu Ishida Kohei Arai Yukio Akita Mitsunori Miyanari Yusuke Minami Tsutomu Yotsuya Masaru Kato Kazuo Satoh Mayumi Uno Hisashi Shimakage Shigehito Miki Zhen Wang 《Physica C: Superconductivity and its Applications》2010,470(19):730-733
The nanofabrication of superconductors yields various interesting features in superconducting properties. A variety of different imaging techniques have been developed for probing the local superconducting profiles. A scanning pulsed laser microscope has been developed by the combination of the XYZ piezo-driven stages and an optical fiber with an aspheric focusing lens. The scanning laser microscope is used to understand the position-dependent properties of a superconducting MgB2 stripline of length 100 μm and width of 3 μm under constant bias current. Our results show that the superconducting stripline can clearly be seen in the contour image of the scanning laser microscope on the signal voltage. It is suggested from the observed image that the inhomogeneity is relevant in specifying the operating conditions such as detection efficiency of the sensor. 相似文献
728.
729.
Toshifumi Satoh Tomoko Imai Yoshikazu Kitajyo Takahiro Maeda Atsushi Narumi Harumi Kaga Noriaki Kaneko Toyoji Kakuchi 《Macromolecular Symposia》2004,217(1):39-46
The thermally induced cationic polymerizations of 1,6-anhydro-β-D -glucopyranose ( 1a ), 1,6-anhydro-β-D -mannopyranose ( 1b ) and 1,6-anhydro-β-D -galactopyranose ( 1c ) as a latent cyclic AB4-type monomer were carried out using (S-2-butenyl)tetramethylenesulfonium hexafluoroantimonate ( 2 ) as an initiator. The solution polymerization in propylene carbonate proceeded without gelation to produce the water-soluble hyperbranched polysaccharides ( 3a-c ) with controlled molecular weights and narrow polydispersities. The degree of branching (DB), estimated by the methylation analysis of 3a-c , was in the range of 0.38 – 0.49. The thermally induced cationic polymerization of 1a-c using 2 is a facile method leading to a hyperbranched polysaccharide with a high DB value. 相似文献