排序方式: 共有104条查询结果,搜索用时 15 毫秒
91.
Cyclisation of bromides 4a-f mediated by tributyltin hydride affords predominantly the trans piperidines 5a-f with modest diastereomeric ratios, while cyclisation with tris(trimethylsilyl)silane affords the same products with diastereomeric ratios of up to 99 : 1. 相似文献
92.
The existing measurements of quarkonium polarization in proton-antiproton and proton-nucleus collisions are puzzling. We highlight issues which are often underestimated in the experimental analyses: the importance of the choice of the experimental acceptance on the comparison between experimental measurements and theoretical calculations. New measurements must provide more detailed information, such that physical conclusions can be derived without relying on model-dependent assumptions. We also describe a frame-invariant formalism which minimizes the dependence of the measurements on the experimental acceptance, facilitates the comparison with theoretical calculations, and probes systematic effects due to experimental biases. 相似文献
93.
Hermine Biermé Hans-Peter Scheffler 《Journal of Fourier Analysis and Applications》2008,14(2):180-202
An approximation of the linear fractional stable motion by a Fourier sum is presented. In the continuous sample path case
precise error bounds are derived. This approximation method is used to develop a simulation method of the sample path of linear
fractional stable motions.
The second author was partially supported by NSF grant DMS-0417869. 相似文献
94.
Shubham Dutta Shengwen Yang Rajeshwer Vanjari Rajendra K. Mallick Vincent Gandon Prof. Dr. Akhila K. Sahoo 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(27):10877-10882
A three-component Pd-catalyzed coupling of ynamides, aryl diazonium salts, and aryl boronic acids for the synthesis of novel triaryl-substituted enamides is described. This transformation represents the first example of an umpolung regioselective unsymmetrical syn-1,2-diarylation/aryl-olefination of ynamides. The aryl moieties of the diazonium salt (electrophile) and boronic acid (nucleophile) are explicitly incorporated in the electrophilic α- and nucleophilic β-position, respectively, of the ynamide, resulting in a single isomer of the N-bearing tetrasubstituted olefin. The scope is broad (68 examples), showing excellent functional-group tolerance. DFT calculations substantiate the rationale of the mechanistic cycle and the regioselectivity. The chemoselectivity and synthetic potential of the enamide products were also studied. 相似文献
95.
[reaction: see text] Co(2)(CO)(6)-complexed alkynyl pinacolborane derivatives are readily transformed with functional group tolerance into fused arylboronates via the [2 + 2 + 2]cycloaddition to alpha,omega-diynes. 相似文献
96.
Hermine Biermé Lionel Moisan Frédéric Richard 《Journal of computational and graphical statistics》2013,22(3):885-904
In this article, we propose a method for simulating realizations of two-dimensional anisotropic fractional Brownian fields (AFBF) introduced by Bonami and Estrade. The method is adapted from a generic simulation method called the turning-band method (TBM) due to Matheron. The TBM reduces the problem of simulating a field in two dimensions by combining independent processes simulated on oriented bands. In the AFBF context, the simulation fields are constructed by discretizing an integral equation arising from the application of the TBM to nonstationary anisotropic fields. This guarantees the convergence of simulations as the step of discretization is decreased. The construction is followed by a theoretical study of the convergence rate (the detailed proofs are available in the online supplementary materials). Another key feature of this work is the simulation of band processes. Using self-similarity properties, processes are simulated exactly on bands with a circulant embedding method, so that simulation errors are exclusively due to the field approximation. Moreover, we design a dynamic programming algorithm that selects band orientations achieving the optimal trade-off between computational cost and precision. Finally, we conduct a numerical study showing that the approximation error does not significantly depend on the regularity of the fields to be simulated, nor on their degree of anisotropy. Experiments also suggest that simulations preserve the statistical properties of the original field. 相似文献
97.
Gandon V Aubert C Malacria M Vollhardt KP 《Chemical communications (Cambridge, England)》2008,(13):1599-1601
In the presence of CpCo(C(2)H(4))(2), alpha,omega-diynes undergo hydroaminative coupling with amides to furnish new dienamides with control of regio- and stereochemistry. 相似文献
98.
99.
Geny A Leboeuf D Rouquié G Vollhardt KP Malacria M Gandon V Aubert C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(19):5408-5425
A series of 1,3- and 1,4-diboryl-1,3-cyclohexadienes have been prepared by intermolecular CoCp-mediated [2+2+2] cocyclizations of alkynylboronic pinacolate esters with alkenes, followed by oxidative demetallation with iron(III) chloride. The effect of substitution at the borylated alkyne on chemo- and regioselectivities has been studied, suggesting steric control. The proper choice of substituents allowed the preparation of 1,3-diborylated cyclohexadienes in a highly selective manner. Alternatively, 1,4-diborylated cyclohexadienes could be prepared from diborylated diynes. The scope of this reaction has been examined and found to include electron-poor, electron-rich, linear, and cyclic alkenes. The diborylated cyclohexadienes were submitted to single or double Suzuki-Miyaura cross-coupling reactions with haloarenes to afford polyarylated systems. The mechanism of the title reaction, including the regioselectivity of the cycloaddition steps, has been analyzed by means of DFT computations. 相似文献
100.