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A short synthesis of the chiral oxazoline 10 (>95% e.e.) in six steps from chloroacetylferrocene is described. The ligand can be used successfully in an asymmetric Pd(0)-catalyzed allylic alkylation reaction. 相似文献
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Racemic 1-acetyl-2-methoxymethylferrocene, (±)-1 was subjected to asymmetric reduction with two different methodologies and complementary results were obtained. When the reduction of (±)-1 was carried out in the presence of CBS-oxazaborolidine catalyst and BH3·Me2S as the hydrogen source, both enantiomers of the substrate were converted with comparable reaction rates and selectivities. The corresponding diastereoisomeric ferrocenylalcohols 3a and 3b were obtained in a 1:1 ratio and >90% enantiomeric excess; this reaction profile being related with a parallel kinetic resolution with high ds1 and ds2 diastereofacial selectivities. On the contrary, the transfer hydrogenation of (±)-1 with HCOOH/triethylamine in the presence of (R,R)-Noyori’s catalyst proceeded via classical kinetic resolution, so that the formed (?)-3b or unreacted (+)-1 could be obtained in highly enantiopure form before or beyond 50% of the substrate conversion, respectively. Alcohol 3b with an (1Rp,S)- or (1Sp,R)-configuration is not easily accessible by the diastereoselective metallation/electrophilic quenching sequence routinely applied in the synthesis of planar chiral ferrocenes. As a result, the described procedures provide a valuable access to this useful starting material for the synthesis of homochiral related derivatives. 相似文献
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This column is a forum for discussion of mathematical communities throughout the world, and through all time. Our definition
of “mathematical community” is the broadest. We include “schools” of mathematics, circles of correspondence, mathematical
societies, student organizations, and informal communities of cardinality greater than one. What we say about the communities
is just as unrestricted. We welcome contributions from mathematicians of all kinds and in all places, and also from scientists,
historians, anthropologists, and others. 相似文献
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Patti GJ 《Journal of separation science》2011,34(24):3460-3469
Metabolomics has rapidly become a profiling technique of choice for biomarker elucidation and molecular diagnostics in addition to studies focused on understanding disease pathogenesis. Key to the success of metabolomics in these areas has been the techniques to separate and analyze the chemically diverse group of compounds comprising the metabolome by using global and untargeted approaches. Untargeted metabolomic efforts have the goal of examining as many metabolites as possible simultaneously and most frequently use an LC/MS-based approach. Here, the importance of LC in an untargeted metabolomic workflow is outlined and separation strategies for optimization are reviewed within the context of these criteria. 相似文献
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M. Masson F. Patti L. Cappellini P. Germain L. Jeanmaire 《Journal of Radioanalytical and Nuclear Chemistry》1983,77(1):247-255
Determination of99Tc in two biological indicators,Fucus sp. andPatella sp., of the French coast of the Channel showed that this radionuclide found in small amounts, was dispersed eastwards from the
La Hague reprocessing fuel plant. However,99Tc trace amounts were also detected in the river Seine bay and in the bay of Mont St. Michel, which confirms the great mobility
of this element.
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The evolution of85Kr concentrations in the atmosphere has been followed in the Northern hemisphere (France) from June 1966 to February 1979
and in the Southern hemisphere from March 1968 to October 1977 (Tahiti and Terre Adélie). The growth observed during the years
1966–1968 (1.8 pCi·m−3 per year) in the Northern hemisphere did not continue in 1969, 1970, 1971, during which period a constant level at 14.8 pCi·m−3 per year and even a decrease (12.9 pCi·m−3 in 1971) were noticed; this was followed by a new increase of about 0.9 pCi·m−3 per year. In the Southern hemisphere, a regular groth from 1968 to 1974 (0.9 pCi·m−3 per year) was followed by values stabilized around 14.5 pCi·m−3. The curve illustrating the evolution of the Krypton specific activity in the Northern hemisphere from 1954 to February 1979
shows that this increased in a discontinuous way from 1 to 40 disintegrations per minute; nevertheless the present atmospheric
activity is very low with a value of only 8·10−5 MPC.
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A mild phase-transfer catalytic reaction has been conducted to O-alkylate the acidic functions of a lignite humic acid (HA), using tetrabutylammonium hydroxide as the phase-transfer catalyst.
The HA acidic functional groups were made to react, in tetrahydrofuran, by nucleophilic substitution with several alkyl halides—methyl
iodide, and ethyl, propyl, and butyl, and benzyl bromide. The occurrence of the O-alkylation reaction was assessed by elemental analysis and 1H NMR, CPMAS 13C NMR, and FTIR spectroscopy. Bonding of alkyl groups increased the carbon and hydrogen content and the H/C ratios of all
the humic reaction products. Increased nitrogen in the reaction products suggested incomplete removal of the phase-transfer
catalyst after purification of the alkylated HA. 1H NMR and CPMAS 13C NMR spectra of alkylated products provided evidence of the successful occurrence of the alkylation reactions. Infrared spectra
confirmed the NMR results, revealing the characteristic absorption of newly formed alkyl and aryl ethers and esters in the
alkylated products and C–H stretching in the aromatic ring of the benzylated derivative. These findings indicate that humic
matter can be successfully alkylated with several different alkylating groups by catalysed phase-transfer reaction. This O-alkylation reaction has the advantage of being mild, versatile, and high-yielding compared with traditional methylation reactions
applied to HA. The possibility of introducing different alkyl groups into the HA by a mild phase-transfer reaction may become
useful by enabling improved fractionation of humic supramolecular associations and further understanding of the molecular
nature of humic substances. 相似文献