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121.
The phenyliodonium ylide of 2-hydroxy-1,4-naphthoquinone reacts with aminoesters, ureas, aminoalcohols and aminophenols in refluxing dichloromethane to afford good yields of indanedione 2-carboxamido compounds, that in solution exist in an enol-amide form. The same reactants in a copper-catalyzed reaction afford mainly the corresponding N-arylo compounds. Arylhydrazines are mainly oxidized by the ylide and arylation occurs only in a low yield. 相似文献
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[reaction: see text] A comparative kinetic study of seven ligands is presented which clearly shows that a slight difference in the substitution pattern of the aryl group on the amine moiety of the ligand dramatically alters the activity of the resulting iridium catalyst. Ligand L6 shows the most impressive kinetics as well as the highest enantioselectivities. 相似文献
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125.
The primary process of vision, consisting of photochemical isomerization ofcis totrans retinal, occurs at three different wavelengths to enable color vision. According to current evidence the successive red shifts to higher wavelength absorption is due to the relative displacement of ions in the vicinity of the chromophore. Free-electron modeling of the absorption spectrum shows that a relative displacement of the counter-ion, associated with the quaternary nitrogen, by 0.5 Å is sufficient to cause the red shift needed to cover the entire spectrum. 相似文献
126.
Abstact: We introduce generalizations of earlier direct methods for constructing large sets of t‐designs. These are based on assembling systematically orbits of t‐homogeneous permutation groups in their induced actions on k‐subsets. By means of these techniques and the known recursive methods we construct an extensive number of new large sets, including new infinite families. In particular, a new series of LS[3](2(2 + m), 8·3m ? 2, 16·3m ? 3) is obtained. This also provides the smallest known ν for a t‐(ν, k, λ) design when t ≥ 16. We present our results compactly for ν ≤ 61, in tables derived from Pascal's triangle modulo appropriate primes. © 2000 John Wiley & Sons, Inc. J Combin Designs 9: 40–59, 2001 相似文献
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128.
Marc Magre Javier Mazuela Montserrat Diéguez Oscar Pàmies Alexandre Alexakis 《Tetrahedron: Asymmetry》2012,23(1):67-71
A phosphite–phosphoroamidite and diphosphoroamidite ligand library was applied in the Cu-catalyzed allylic substitution of a range of cinnamyl-type substrates using several organometallic nucleophiles. Results indicated that selectivity depended strongly on the ligand parameters (position of the phosphoroamidite group at either C-5 or C-3 of the furanoside backbone, as well as the configuration of C-3, the introduction of a second phosphoroamidite moiety, the substituents and configurations in the biaryl phosphite/phosphoroamidite moieties), the nature of the leaving group of the substrate and the alkylating reagent. Good enantioselectivities (up to 76%) and activity combined with high regioselectivities were obtained. 相似文献
129.
Demetrios N. Nicolaides Konstantinos E. Litinas Ioannis Psaroulis Aristea Makri Spyros Adamopoulos 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2104-2111
Abstract Dimethyl (chromen-3-yl)-(dialkoxyphosphoryl)succinates are prepared from the reaction of 4-hydroxycoumarin with DMAD and P(OR)3. 4-Hydroxy-1-methylquinolinone reacts with DMAD and P(OEt)3 to give dimethyl (quinoline-3-yl)-(diethoxyphosphoryl)-succinate. GRAPHICAL ABSTRACT 相似文献
130.
Dr. Matthieu Tissot Prof. Alexandre Alexakis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(34):11352-11363
The copper‐catalysed conjugate addition of trialkylaluminium and dialkylzinc reagents to polyconjugated nitroolefins (nitrodiene and nitroenyne derivatives) is reported. A reversed Josiphos ligand L7 allows for the selective 1,4‐ or 1,6‐addition with high enantioselectivities. 相似文献