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51.
Stereocontrolled Synthesis of 1,5‐Stereogenic Centers through Three‐Carbon Homologation of Boronic Esters 下载免费PDF全文
Phillip J. Unsworth Dr. Daniele Leonori Prof. Varinder K. Aggarwal 《Angewandte Chemie (International ed. in English)》2014,53(37):9846-9850
Allylic pinacol boronic esters are stable toward 1,3‐borotropic rearrangement. We developed a PdII‐mediated isomerization process that gives di‐ or trisubstituted allylic boronic esters with high E selectivity. The combination of this method with lithiation–borylation enables the synthesis of carbon chains that bear 1,5‐stereogenic centers. The utility of this method has been demonstrated in a formal synthesis of (+)‐jasplakinolide. 相似文献
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S. K. Aggarwal D. Alamelu P. M. Shah N. N. Mirashi 《Journal of Radioanalytical and Nuclear Chemistry》2007,273(3):771-774
Determination of 241Am/243Am ratios is required for vanous purposes including assay of Am by isotope dilution techniques. Alpha-spectrometry on electrodeposited
sources is a preferred technique for this determination. However, there is an inherent problem of tail contribution which
necessitates the use of suitable algorithms to account for the same. Recently, in the frame of a Coordinated Research Program
(CRP) of the International Atomic Energy Agency (IAEA), WinALPHA software has been developed which is a combination of an
asymmetrical Gaussian for the main part of the peak and a low energy function. Therefore, it was of interest to compare the
use of this algorithm with the routinely used method, in our laboratory, based on geometric progression (G. P.) decrease.
Since, there are no reference materials available commercially for 241Am/243Am ratios, synthetic mixtures covening a wide range (0.3 to 2.0) of 241Am/243Am α-activity ratios were used and un-ignited electrodeposited sources were prepared for α-spectrometry. The α-spectra obtained using PIPS detector, were evaluated using the two algonthms The 241Am/243Am α-activity ratios obtained were also compared with those determined by thermal ionization mass spectrometry (TIMS). An agreement
of about 1% was obtained in the 241Am/243Am ratios determined by the two methods and also by using the two algorithms for α-spectrum evaluation. 相似文献
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The synthesis of imidazolinium salts from the reaction of formamidines and (2-bromoethyl)diphenylsulfonium triflate is described. A variety of symmetrical and unsymmetrical imidazolinium triflate salts were synthesized in high yield in short reaction times under mild conditions. Aromatic and aliphatic N-substituents work well. The reaction is proposed to proceed via generation of a vinyl sulfonium salt intermediate from the bromoethylsulfonium triflate. 相似文献
55.
StephenP. Thomas VarinderK. Aggarwal 《Angewandte Chemie (International ed. in English)》2009,48(11):1896-1898
A breakthrough in the asymmetric hydroboration of notoriously difficult 1,1‐disubstituted alkenes using a new family of highly effective hydroboration reagents is described (see scheme). The intermediate boranes can be oxidized to alcohols or used in Suzuki–Miyaura cross‐coupling reactions.
56.
Ravi Aggarwal Durairaj Baskaran 《Journal of polymer science. Part A, Polymer chemistry》2011,49(23):5049-5056
Hydrated sodium montmorillonite (Na‐clay) has been used as a catalyst support for the heterogeneous atom transfer radical polymerization of benzyl methacrylate in the presence of various concentrations of water, reducing agent, and CuBr2 in anisole at ambient temperature. The polymerization was promoted via reduction of CuII to CuI through the addition of sodium ascorbate (NaAsc) as a reducing agent in aqueous solution. The polymerizaton proceeded in a controlled manner and produced poly(benzyl methacylate) with moderately narrow molecular weight distribution (MWD) when performed under optimum conditions of hydration (10 wt % ≤ H2O/Na‐clay ≤ 21 wt %) and reducing agent (0.15 ≤ [NaAsc]/[I] ≤ 0.23). The polymerization was uncontrolled if hydration and NaAsc exceed above their optimum range of concentrations. Apparent rate of the polymerization (kapp) increased in the presence of decane–anisole (1/3, v/v) mixture solvent. Selective adsorption of decane at the interfaces of the hydrated clay was attributed for the rate enhancement due to increased polymer and hydrophobic interface interaction. The polymerization progressed in a controlled manner as confirmed by the first‐order time‐conversion plot, linear increase in molecular weights, and moderately narrow MWDs over conversion. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
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We have performed numerical analysis of the one-dimensional dynamics of the cylindrical/spherical dust ion acoustic shock waves in unmagnetized dusty plasma consisting of positive ions, immobile dust particles, and nonextensive distributed cold and hot electrons. A multiple-scale expansion method is used to derive Burgers Equation (BE) and modified Burgers equation (MBE) by including higher order nonlinearity. The basic characteristics of the shock waves have been analysed numerically and graphically for different physical parameters relevant to Saturn' E ring through 2D figures. The parametric dependence of dust ion acoustic shock waves on some plasma parameters nonextensive index, density, and temperature of cold and hot electrons, concentration of dust particles, thermal effects and kinematic viscosity of ions is explored. Furthermore, it is found that the nonplanar geometry effects have an important impact on the establishment of shock waves. The amplitude of the wave decreases faster as one departs away from the axis of the cylinder or centre of the sphere. Such decaying behaviour continues as time progresses. It is also found that an increasing dust concentration decreases the amplitude of the dust ion acoustic shock waves. 相似文献