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Diastereoselectively Switchable Asymmetric Haloaminocyclization for the Synthesis of Cyclic Sulfamates 下载免费PDF全文
Dr. Yunfei Cai Pengfei Zhou Prof. Dr. Xiaohua Liu Jiannan Zhao Dr. Lili Lin Prof. Dr. Xiaoming Feng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(17):6386-6389
An asymmetric synthesis of cyclic sulfamates by catalytic haloaminocyclization of primary sulfamate ester derivatives is described. The remarkable reversal of diastereoselectivity was found to be dependent on the halogen source and the chiral catalyst. By using privileged complexes of N,N′‐dioxides with Sc(OTf)3 or Lu(OTf)3 as the catalyst, a variety of enantioenriched syn‐ and anti‐cyclic sulfamates or related trans‐aziridines could be obtained in 92–99 % ee and up to 97 % yield. 相似文献
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In this paper, a new physically based constitutive model is developed for hexagonal close-packed metals, especially the Ti-6 A1-4V alloy, subjected to high strain rate and different temperatures based on the microscopic mechanism of plastic deformation and the theory of thermally activated dislocation motion. A global analysis of constitutive parameters based on the Latin Hypercube Sampling method and the Spearman's rank correlation method is adopted in order to improve the identification efficiency of parameters. Then, an optimal solution of constitutive parameters as a whole is obtained by using a global genetic algorithm composed of an improved niche genetic algorithm, a global peak determination strategy and the local accurate search techniques. It is concluded that the proposed constitutive modal can accurately describe the Ti-6 Al-4V alloy's dynamic behavior because the prediction results of the model are in good agreement with the experimental data. 相似文献
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A novel device with a large cavity is investigated with regard to pressure capacity. This device is the multilayer stagger-split die (MSSD) that employs one or more supported rings and the multilayered divided body assemblage. The divided bodies are arranged in a staggered manner between adjacent layers. The pressure capacity of this device is calculated based on different failure criteria and using the simulation-based optimization approach. The results are compared with those of the belt-type die (BTD). A comparative experiment is also carried out to verify the simulated results. We conclude that the conditionality of pressure capacity of MSSD is related to die size. And MSSD can bear higher pressure than the BTD. 相似文献
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Burkeite formation is important in saline evaporites and in pipe scales. Burkeite is an anhydrous sulphate-carbonate with an apparent variable anion ratio. Such a formula with two oxyanions lends itself to vibrational spectroscopy. Two symmetric sulphate stretching modes are observed, indicating at least at the molecular level the nonequivalence of the sulphate ions in the burkeite structure. The strong Raman band at 1065 cm?1 is assigned to the carbonate symmetric stretching vibration. The series of Raman bands at 622, 635, 645, and 704 cm?1 are assigned to the ν4 sulphate bending modes. The observation of multiple bands supports the concept of a reduction in symmetry of the sulphate anion from T d to C 3v or even C 2v. 相似文献
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This article deals with a diffusive cooperative model with state-dependent delay which is assumed to be an increasing function of the population density with lower and upper bounds. For the cooperative DDE system, the positivity and boundedness of solutions are firstly given. Using the comparison principle of the state-dependent delay equations obtained, the stability criterion of model is analyzed both from local and global points of view. When the diffusion is properly introduced, the existence of traveling waves is obtained by constructing a pair of upper–lower solutions and Schauder's fixed point theorem. Calculating the minimum wave speed shows that the wave is slowed down by the state-dependent delay. Finally, the traveling wavefront solutions for large wave speed are also discussed, and the fronts appear to be all monotone, regardless of the state dependent time delay. This is an interesting property, since many findings are frequently reported that delay causes a loss of monotonicity, with the front developing a prominent hump in some other delay models. 相似文献