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1.
Deerenberg S Schrekker HS van Strijdonck GP Kamer PC van Leeuwen PW Fraanje J Goubitz K 《The Journal of organic chemistry》2000,65(16):4810-4817
A series of chiral phosphine-phosphite ligands 1-6 have been synthesized and used in the enantioselective palladium-catalyzed reaction of rac-1,3-diphenyl-2-propenyl acetate with dimethyl malonate as nucleophile. Ligands 1a, 2, 3, 5a, 6a, and 6b have been synthesized starting from racemic tert-butylphenylphosphinoborane. The use of dynamically resolved Li phosphide (-)-sparteine provided the optically pure ligands. Crystals of the allylpalladium (6a) complex were obtained, suitable for X-ray crystal structure determination. The X-ray crystal structure of the allylpalladium (6a) complex revealed a longer palladium-carbon bond distance trans to the phosphine moiety indicating that the attack of the nucleophile takes place at the carbon trans to the phosphine moiety. This was confirmed by the fact that the phosphine moiety did not affect the enantioselectivity directly. Under mild reaction conditions, enantioselectivities up to 83% were obtained (25 degrees C) with ligand 1e. Systematic variation of the ligand bridge and the phosphite moiety showed that the configuration of the product is controlled by the atropisomerism of the biphenyl substituent at the phosphite moiety. The conformation of the biphenyl group, in turn, is controlled by the substituent at the chiral carbon in the bridge. Ligands with large bite angles yielded higher enantioselectivities. 相似文献
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Abdurashitov JN Gavrin VN Girin SV Gorbachev VV Ibragimova TV Kalikhov AV Khairnasov NG Knodel TV Kornoukhov VN Mirmov IN Shikhin AA Veretenkin EP Vermul VM Yants VE Zatsepin GT Bowles TJ Nico JS Teasdale WA Wark DL Cherry ML Karaulov VN Levitin VL Maev VI Nazarenko PI Shkol'nik VS Skorikov NV Cleveland BT Daily T Davis R Lande K Lee CK Wildenhain PW Khomyakov YS Zvonarev AV Elliott SR Wilkerson JF 《Physical review letters》1996,77(23):4708-4711
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Petra DG Kamer PC Spek AL Schoemaker HE van Leeuwen PW 《The Journal of organic chemistry》2000,65(10):3010-3017
A new class of efficient catalysts was developed for the asymmetric transfer hydrogenation of unsymmetrical ketones. A series of chiral N,S-chelates (6-22) was synthesized to serve as ligands in the iridium(I)-catalyzed reduction of ketones. Both formic acid and 2-propanol proved to be suitable as hydrogen donors. Sulfoxidation of an (R)-cysteine-based aminosulfide provided a diastereomeric ligand family containing a chiral sulfur atom. The two chiral centers of these ligands showed a clear effect of chiral cooperativity. In addition, aminosulfides containing two asymmetric carbon atoms in the backbone were synthesized. Both the sulfoxide-containing beta-amino alcohols and the aminosulfides derived from 1,2-disubstituted amino alcohols gave rise to high reaction rates and moderate to excellent enantioselectivities in the reduction of various ketones. The enantioselective outcome of the reaction was favorably affected by selecting the most appropriate hydrogen donor. Enantioselectivities of up to 97% were reached in the reduction of aryl-alkyl ketones. 相似文献
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Sandee AJ van Der Veen LA Reek JN Kamer PC Lutz M Spek AL van Leeuwen PW 《Angewandte Chemie (International ed. in English)》1999,38(21):3231-3235
By a sol-gel process a rhodium complex containing a diphosphane with a large natural P-Rh-P bite angle is covalently anchored in a silica matrix (see picture). The immobilized catalyst is a very selective hydroformylation catalyst that is completely and conveniently separated from the product and can be reused in numerous cycles. 相似文献
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J. N. Abdurashitov V. N. Gavrin S. V. Girin V. V. Gorbachev T. V. Ibragimova A. V. Kalikhov N. G. Khairnasov T. V. Knodel I. N. Mirmov A. A. Shikhin E. P. Veretenkin V. M. Vermul V. E. Yants G. T. Zatsepin T. J. Bowles W. A. Teasdale D. L. Wark J. S. Nico M. L. Cherry B. T. Cleveland R. Davis Jr. K. Lande P. S. Wildenhain S. R. Elliott J. F. Wilkerson 《Physics of Atomic Nuclei》2000,63(6):943-950
The solar-neutrino-capture rate measured by the Russian-American Gallium Experiment on metallic gallium during the period from January 1990 to December 1997 is (67.2 ?7.0?3.0 +7.2+3.5 ) SNU, where the uncertainties are statistical and systematic, respectively. This result represents a 7σ depression in the neutrino flux in relation to the predicted standard-solar-model rates. The experimental procedures used and data analysis are presented. 相似文献
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Günther Wildenhain 《Mathematische Annalen》1965,161(1):1-23
Ohne Zusammenfassung 相似文献
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Zusammenfassung Fraktionierte Torffulvosäuren geben bei der Ätherspaltung mit Natrium in Pyridin in Abhängigkeit von der Reaktionszeit 2,6-Dimethoxyphenol, o-Methoxybrenzcatechin und Diguajacylmethan, womit die strukturelle Verwandtschaft zum Lignin offensichtlich ist.
Reductive cleavage of peat fulvic acids by sodium in pyridine
Peat fulvic acids, obtained by fractionation on ion-exchangers, give 2.6-dimethoxyphenol, o-methoxycatechol and diguaiacylmethane on ether cleavage with sodium in pyridine in dependence on the reaction time. The structural relationship to lignin, therefore, is obvious.相似文献
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