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排序方式: 共有174条查询结果,搜索用时 31 毫秒
81.
Thomas Guérin Dr. Nadiia V. Pikun Ryutaro Morioka Dr. Armen Panossian Dr. Gilles Hanquet Dr. Frédéric R. Leroux 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(65):14852-14855
The synthesis of trifluoromethylthiolated ketenimines is herein described. They are easily synthesized from the corresponding α-trifluoromethylthiolated oximes upon activation with triflic anhydride and a base. The presumed nitrilium ion resulting from the Beckmann rearrangement is deprotonated to lead to the key intermediate, whose stability brought by the fluorinated substituent was unforeseeable. The reaction of these new building blocks with a variety of nucleophiles affords a vast array of cyclic and acyclic products bearing the valuable SCF3 moiety. 相似文献
82.
83.
Armen G. Khachaturyan 《Acta Mechanica Solida Sinica》2012,25(4):429-440
Computer modeling and simulation for the Pb(Zr 1 x Ti x )O 3 (PZT) system reveal the role of polar anisotropy on the giant anhysteretic response and structural properties of morphotropic phase boundary (MPB) ferroelectrics. It is shown that a drastic reduction of the composition- dependent polar anisotropy near the MPB flattens energy surfaces and thus facilitates reversible polarization rotation. It is further shown that the polar anisotropy favors formation of polar domains, promotes phase decomposition and results in a two-phase multidomain state, which response to applied electric field is anhysteretic when the polar domain reorientation is only caused by polarization rotation other than polar domain wall movement. This is the case for the decomposing ferroelectrics under a poling electric field with the formation of a two-phase multidomain microstructure, wherein most domain walls are pinned at the two-phase boundaries. Indication of the microstructure dependence of the anhysteretic strain response opens new avenues to improve the piezoelectric properties of these materials through the microstructure engineering. 相似文献
84.
Armen Panossian Héctor Fernández-Pérez Dana Popa Anton Vidal-Ferran 《Tetrahedron: Asymmetry》2010,21(18):2281-2288
A library of highly modular P-OP ligands have been evaluated in Pd-catalysed allylic substitutions with C- and N-nucleophiles. Catalyst optimisation via a variation of the phosphino and phosphite substituents led to a ‘lead’ catalyst, which efficiently mediated the allylic substitutions when various combinations of substrates and nucleophiles were tested. Ground-state calculations were carried out and these allowed a clearer understanding of the stereochemical outcome of the reaction. 相似文献
85.
86.
Amos B. Smith III Qiyan Lin Victoria A. Doughty Linghang Zhuang Mark D. McBriar Jeffrey K. Kerns Armen M. Boldi Noriaki Murase William H. Moser Christopher S. Brook Clay S. Bennett Kiyoshi Nakayama Masao Sobukawa Robert E. Lee Trout 《Tetrahedron》2009,65(33):6470-14053
Evolution of a convergent synthetic strategy to access (+)-spongistatin 2 (2), a potent cytotoxic marine macrolide, is described. Highlights of the synthesis include: development of a multicomponent dithiane-mediated linchpin union tactic, devised and implemented specifically for construction of the spongistatin AB and CD spiro ring systems; application of a CaII ion controlled acid promoted equilibration to set the thermodynamically less stable axial-equatorial stereogenicity in the CD spiroketal; use of sulfone addition/Julia methylenation sequences to unite the AB and CD fragments and introduce the C(44)-C(51) side chain; and fragment union and final elaboration to (+)-spongistatin 2 (2) exploiting Wittig olefination to unite the advanced ABCD and EF fragments, followed by regioselective Yamaguchi macrolactonization and global deprotection. Correction of the CD spiro ring stereogenicity was subsequently achieved via acid equilibration in the presence of CaII ion to furnish (+)-spongistatin 2 (2). The synthesis proceeded with a longest linear sequence of 41 steps. 相似文献
87.
Sargsyan A Hakhumyan G Leroy C Pashayan-Leroy Y Papoyan A Sarkisyan D 《Optics letters》2012,37(8):1379-1381
A simple and efficient scheme based on a one-dimensional nanometric-thin cell filled with Rb and strong permanent ring magnets allows direct observation of the hyperfine Paschen-Back regime on the D(1) line in the 0.5-0.7 T magnetic field. Experimental results are perfectly consistent with the theory. In particular, with σ(+) laser excitation, the slopes of the B-field dependence of frequency shifts for all 10 individual transitions of (85,87)Rb are the same and equal to 18.6 MHz/mT. Possible applications for magnetometry with submicron spatial resolution and tunable atomic frequency references are discussed. 相似文献
88.
Iimura S Overman LE Paulini R Zakarian A 《Journal of the American Chemical Society》2006,128(40):13095-13101
A convergent, enantioselective total synthesis of (+)-guanacastepene N was developed that features a 7-endo Heck cyclization as the key step. In the course of this synthesis, short syntheses of the enantiomerically pure cyclopentenone and cyclohexene building blocks 5 and 6, which constitute A and C ring fragments of guanacastepene N, were developed. These fragments were linked by a challenging conjugate addition reaction that also generated the C11 quaternary carbon stereocenter. Regioselective 7-endo Heck cyclization gave rise to a tricyclic intermediate, which was elaborated to complete the first total synthesis of guanacastepene N and the second enantioselective total synthesis of a guanacastepene natural product. 相似文献
89.
90.
Armen Shirikyan 《Communications in Mathematical Physics》2006,266(1):123-151
The paper is devoted to studying the problem of controllability for 3D Navier–Stokes equations in a bounded domain. We develop the method introduced by Agrachev and Sarychev in the 2D case and establish a sufficient condition under which the problem in question is approximately controllable by a finite-dimensional force. In the particular case of a torus, it is shown that our sufficient condition is fulfilled for a control of low dimension not depending on the viscosity.
To the undying memory of my uncle, Professor Sargis A. Markosyan 相似文献