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排序方式: 共有119条查询结果,搜索用时 531 毫秒
101.
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Carreno MC Garcia Ruano JL Urbano A Remor CZ Arroyo Y 《The Journal of organic chemistry》2000,65(2):453-458
Diels-Alder reactions of (SS)-2-(2'-methoxynaphthylsulfinyl)-1, 4-benzoquinone (1b), 2-(p-methoxyphenylsulfinyl)-1,4-benzoquinone (1c), and 2-(p-nitrophenylsulfinyl)-1,4-benzoquinone (1d) with cyclopentadiene are reported. These cycloadditions allowed the highly chemo- and stereoselective formation of both diastereoisomeric endo-adducts resulting from reaction on the unsubstituted double bond C(5)-C(6) of quinones working under thermal and Eu(fod)(3)- or BF(3).OEt(2)-catalyzed conditions. The synthesis of endo-adduct [4aS,5S,8R,8aR,SS]-9d resulting from cycloaddition on the substituted C(2)-C(3) double bond was achieved in a chemo- and diastereoselective way from quinone 1d in the presence of ZnBr(2). The reactivity and selectivity of the process proved to be dependent on the electron density of the arylsulfinyl group. 相似文献
103.
[reaction: see text] An efficient, user-friendly procedure for the oxidation of alcohols using IBX is described. Simply heating a solution of the alcohol in the presence of suspended IBX followed by filtration and removal of the solvent gives excellent yields of the corresponding carbonyl compounds. We illustrate this procedure with a panel of primary and secondary alcohol substrates and note that it allows recycling and reuse of the oxidant. 相似文献
104.
Garcia Ruano JL Barros D Maestro MC Slawin AM Page PC 《The Journal of organic chemistry》2000,65(19):6027-6034
The asymmetric aldol reaction of 1,2-diketones, masked as nonracemic 2-acyl dithiane oxides, with lithium enolates derived from several esters and lactones, proceeds with a high degree of stereocontrol at both carbonyl and enolate prochiral centers, the stereocontrol mainly determined by the configuration of the sulfoxide sulfur atom. The sense of induced stereochemistry observed for ester enolates is different from that seen for lactone enolates. Hydrolysis of the dithiane oxide units of the major diastereoisomerically pure aldol products affords enantiomerically pure tertiary alpha-substituted beta-hydroxy-gamma-ketoesters. 相似文献
105.
Self-organization and chaos in a fluidized bed 总被引:1,自引:0,他引:1
Daw CS Finney CE Vasudevan M van Goor NA Nguyen K Bruns DD Kostelich EJ Grebogi C Ott E Yorke JA 《Physical review letters》1995,75(12):2308-2311
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Microdistribution of lead in human teeth using microbeam synchrotron radiation X‐ray fluorescence (μ‐SRXRF) 下载免费PDF全文
Yufei Wang Aaron Specht Yingzi Liu Lydia Finney Evan Maxey Stefan Vogt Wei Zheng Marc Weisskopf Linda H Nie 《X射线光谱测定》2017,46(1):19-26
Lead (Pb) exposure is known to be associated with adverse effects on human health, especially during the prenatal period and early childhood. The Pb content in teeth has been suggested as a useful biomarker for the evaluation of cumulative Pb exposure. This study was designed to employ the microbeam synchrotron radiation X‐ray fluorescence technique to determine the microdistribution of Pb within the tooth to evaluate the reliability of the technique and the effectiveness of tooth Pb as a biomarker of Pb exposure. The results showed that in the incisor sample, Pb primarily deposited in secondary dentine region close to the pulp and secondarily at enamel exterior. In addition, Pb colocalised with Zn, indicating a positive correlation between Pb and Zn. By contrast, in the two molar samples, Pb accumulated principally in the pulp, and secondarily in the enamel. At the same time, Pb in these two molar samples colocalised with Ca instead of Zn as was observed in the incisor sample. Several batches of line scans further confirmed the conclusions. The feasibility of using microbeam synchrotron radiation X‐ray fluorescence to determine the microdistribution of Pb in teeth and of using the tooth Pb, especially in dentine, as a biomarker was discussed. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
109.
Finney JL Bowron DT Soper AK Loerting T Mayer E Hallbrucker A 《Physical review letters》2002,89(20):205503
The detailed structure of a new dense amorphous ice, VHDA, is determined by isotope substitution neutron diffraction. Its structure is characterized by a doubled occupancy of the stabilizing interstitial location that was found in high density amorphous ice, HDA. As would be expected for a thermally activated unlocking of the stabilizing "interstitial," the transition from VHDA to LDA (low-density amorphous ice) is very sharp. Although its higher density makes VHDA a better candidate than HDA for a physical manifestation of the second putative liquid phase of water, as for the HDA case, the VHDA to LDA transition also appears to be kinetically controlled. 相似文献
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