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排序方式: 共有284条查询结果,搜索用时 46 毫秒
111.
Jahier C Zatolochnaya OV Zvyagintsev NV Ananikov VP Gevorgyan V 《Organic letters》2012,14(11):2846-2849
A general highly regio- and stereoselective palladium-catalyzed head-to-head dimerization reaction of terminal acetylenes is presented. This methodology allows for the efficient synthesis of a variety of 1,4-enynes as single E stereoisomers. Computational studies reveal that this dimerization reaction proceeds via the hydropalladation pathway. 相似文献
112.
A well-established oxidative addition of organic halides (R-X) to N-heterocyclic carbene (NHC) complexes of palladium(0) leads to formation of (NHC)(R)PdII(X)L species, the key intermediates in a large variety of synthetically useful cross-coupling reactions. Typical consideration of the cross-coupling catalytic cycle is based on the assumption of intrinsic stability of these species, where the subsequent steps involve coordination of the second reacting partner. Thus, high stability of the intermediate (NHC)(R)PdII(X)L species is usually taken for granted. In the present study it is discussed that such intermediates are prone to non-classical R-NHC intramolecular coupling process (R = Me, Ph, Vinyl, Ethynyl) that results in removal of NHC ligand and generation of another type of Pd catalytic system. DFT calculations (BP86, TPSS, PBE1PBE, B3LYP, M06, wB97X-D) clearly show that outcome of R-NHC coupling process is not only determined by chemical nature of the organic substituent R, but also strongly depends on the type of solvent. The reaction is most favorable in polar solvents, whereas the non-polar solvents render the products less stable. © 2019 Wiley Periodicals, Inc. 相似文献
113.
Synthesis of novel spiro-condensed 2-amino-4H-pyrans based on 1,2-benzoxathiin-4(3H)-one 2,2-dioxide
Grygoriv Galina V. Lega Dmitry A. Zaprutko Lucjusz Gzella Andrzej K. Wieczorek-Dziurla Ewa Chernykh Valentine P. Shemchuk Leonid A. 《Chemistry of Heterocyclic Compounds》2019,55(3):254-260
Chemistry of Heterocyclic Compounds - A series of new spiro-condensed 2-amino-4H-pyrans were synthesized by three-component interaction of 1,2-benzoxathiin-4(3H)-one 2,2-dioxide, malononitrile, and... 相似文献
114.
Valentine MT Guydosh NR Gutiérrez-Medina B Fehr AN Andreasson JO Block SM 《Optics letters》2008,33(6):599-601
We designed, constructed, and tested a single-beam optical trapping instrument employing twin electro-optic deflectors (EODs) to steer the trap in the specimen plane. Compared with traditional instruments based on acousto-optic deflectors (AODs), EOD-based traps offer a significant improvement in light throughput and a reduction in deflection-angle (pointing) errors. These attributes impart improved force and position resolution, making EOD-based traps a promising alternative for high-precision nanomechanical measurements of biomaterials. 相似文献
115.
Alexander Gorbunov Dr. Nadezhda Sokolova Dr. Elena Kudryashova Prof. Dr. Valentine Nenajdenko Prof. Dr. Vladimir Kovalev Dr. Ivan Vatsouro 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(35):12415-12423
Cone calix[4]arenes and calix[6]arenes bearing two, three, and four short peptide units each having two chiral carbon atoms were prepared. The syntheses were performed by using an efficient modular approach that includes the Ugi preparation of the azido‐peptide followed by its reactions with the propargylated calixarenes under CuAAC (CuI‐catalyzed azide–alkyne cycloaddition) conditions. The three novel multitopic hosts were probed for their ability to bind metal ions by UV titration, and showed the highest complexation efficiency towards copper(II) and lead(II). These two cations possessed quite different complexation modes with copper(II) bound predominantly by multiple‐triazole sites, in contrast to lead(II), which is stabilized mainly by multiple interactions with amide groups of the peptide units. Circular dichroism data for the free chiral hosts, their equimolar mixtures with copper(II) perchlorate and lead(II) perchlorate, and for tertiary mixtures of all three compounds showed the formation of mono‐ and binuclear complexes, or a switching behavior, depending on the structure of the host and the addition order of the cations. 相似文献
116.
117.
Investigation of electron transfer in synthetic polypeptides provides an important probe of how charge entrainment is mediated in redox-active proteins, including photosynthetic reaction centers. Interest in this field has focused increasingly on experimental probes of photoinduced electron transfer kinetics and thermodynamics, and the influence of various features of polypeptide templates (e.g. the hydrogen bonding network, the permanent dipole moment for α-helices) that assemble redox groups for long range charge transfer. A review of the various approaches is presented here with attention to heliogenic peptides and the mediation of photoinduced charge entrainment. 相似文献
118.
Valentine G. Nenajdenko Andrew M. Moiseev Elizabeth S. Balenkova 《Tetrahedron》2005,61(46):10880-10885
EWG-containing thiophene-1,1-dioxides were found to be very active dienophiles in reactions with 1,3-dienes to afford corresponding cycloadducts in mild conditions. A chemo-, regio- and stereoselective cycloaddition was observed. Reaction resulted in formation of derivatives of tetrahydrobenzothiophene-1,1-dioxides in high yields. 相似文献
119.
Lipatov Y Todosijchuk T Chornaya V Menzheres G 《Journal of colloid and interface science》2002,246(1):29-33
Simultaneous competitive adsorption from solutions of mixtures of poly(butyl methacrylate) and polystyrene and adsorption of each component from binary solutions have been studied for three ratios of the adsorbent mass to the solution volume, A/V. It was found that adsorption from both binary and ternary solutions strongly depends on the amount of an adsorbent, adsorption of poly(butyl methacrylate) being preferential. The characteristic adsorption isotherms of both polymers were constructed under conditions of equal equilibrium concentration of each component to estimate the parameters of preferential adsorption and their dependence on the A/V ratio. It was found that the A/V effect plays an important role in adsorption from polymer mixtures and determines the peculiarities of adsorption from polymer mixtures as well as from solution of single polymers. Changing the A/V ratio may be one way to regulate the composition of an adsorption layer consisting of two chemically different polymers. The reasons for the A/V effect are considered in the framework of the concept of the plurality of adsorption equilibria between two chemically different components and between fractions of different molecular mass of each component having various absorbability. 相似文献
120.