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1.
Herbert Waldmann Michael Weigerding Claus Dreisbach Christian Wandrey 《Helvetica chimica acta》1994,77(8):2111-2116
Enantiomerically pure C2-symmetric 1,4-diols embodying bicyclic C-frameworks were synthesized by means of asymmetric carbo-Diels-Alder reactions as key steps (Scheme 1). They were investigated as chiral ligands in the enantioselective addition of ZnEt2 to aromatic aldehydes. In the presence of 20–40 mol-% of the titanates formed from these diols and [Ti(i-PrO)4] at ?78°, the respective 1-arylpropanols were obtained with enantiomer ratios up to 93:7 (Scheme 2, Table). 相似文献
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David A. Evans Edward J. Olhava Jeffrey S. Johnson Jacob M. Janey 《Angewandte Chemie (International ed. in English)》1998,37(24):3372-3375
Air-stable and recyclable , the CuII–(bis)oxazoline complex 1 efficiently catalyzes diastereo- and enantioselective hetero-Diels–Alder reactions between β,γ-unsaturated α-keto acid derivatives 2 and vinyl ethers for the synthesis of substituted dihydropyrans 3 [Eq. (1)]. Results of the crystal structure analysis of 1 in combination with calculations on model compounds indicate the formation of a reactive intermediate through replacement of the two H2O ligands with a chelating substrate. X=OEt, N(OMe)Me; R=alkyl, aryl, alkoxy, thiobenzyl. 相似文献
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CHEN Chien-Tien CHOU Y-Chen KAO Jin-Y LI Tai-Wei LIU Chia-Cheng LI Ying-Chieh CHANG I-Hsin LIN Jin-sheng YEN Chia-Wen 《高等学校化学研究》2001,17(3)
Three C2-symmetric (10R,11R)-diethyl substituted dibenzosuberane (DBS)-based helicenes with varying steric and conjugation demands of their bottom fragments were synthesized. Only the helicene-7a[with the bottom part derived from tetralone was found photo-switchable in reasonable time scale. Photoisomerization of the diastereomerically pure (10R,11R,P)-helicene (7a) at 280 nm led to virtually exclusive formation of the opposite M form-diastereomer 7a′ (7a′/7a = 99.6/0.4). The preferential return of 7a′ to 7a can be effected upon irradiation at 254 nm (7a′/7a = 3G/67) or thermally at 130 7a′/7a = 0/100). The photo-induced switching process amounts to a 133% difference in d.e. (from 99.2% to-34%). The concomitant change of helicene chirality between these two diastereomeric photostationary states augurs well for their potential application as an optical switch in LC materials. To our knowledge, our system serves as the best chirochromic optical switch as compared to the examples possessing similar photochromic properties. 相似文献
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《Tetrahedron: Asymmetry》2000,11(15):3123-3130
A family of C2-symmetric bisphosphinites 3, 5, 7, 9 and bisaminophosphine 11 were prepared and were probed in the prototypical reaction system of palladium-catalyzed asymmetric allylic substitution. The highest ee of 86% was achieved by employing ligand 3. 相似文献
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[reaction: see text] Bissulfoximines have been used as chiral ligands in copper-catalyzed enantioselective Diels-Alder reactions between acryloyl-2-oxazolidinones and cyclopentadiene. After optimizing the ligand structure, the metal source, the counterions, and the solvent, products with up to 93% ee have been obtained. 相似文献
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ZHANG Ru-Zhou Mukund P. Sibi 《有机化学》2003,23(Z1):2-2
Ligand design and synthesis occupy a central theme in asymmetric catalysis. [1] In developing chiral ligands, their design should provide an opportunity for tuning through easy modification of substituents. In a large number of cases, this means starting from a new chiral source. We have been interested in design/synthesis of novel chiral ligands that allow for diversity to be introduced with ease. We have designed a new ligand system containing a core dihydropyrazole moiety with chiraliuy residing remotely to the fluxional group as shown in Scheme 1. There are three points of diversity and these are indicated on the structure. 相似文献
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Kani Zilbeyaz Hamdullah Kilic Melda Sisecioglu Hasan Ozdemir Azize Alayli Güngör 《Tetrahedron: Asymmetry》2012,23(8):594-601
The kinetic resolution of a variety of secondary para-substituted phenylethyl hydroperoxides by Raphanus sativus L. (black radish peroxidase) in the presence of guaiacol is reported. The peroxidase enzyme recognized (R)-configured alkyl aryl hydroperoxides, which furnished optically active (S)-hydroperoxides and (R)-alcohols. Kinetic resolution of tertiary hydroperoxides by the enzyme was unsuccessful. This study also shows how the optically active p-substituted (S)-hydroperoxides obtained can be employed as enantioselective oxidants in the asymmetric Weitz–Scheffer epoxidation of E-chalcone in the presence of KF-Al2O3 as a base. In all cases, a chalcone epoxide with the (αS,βR)-configuration was obtained as the major isomer. Under the optimized reaction conditions, the enantiomeric excess of the chalcone epoxide was obtained in up to 49% in CH3CN at ?40 °C. 相似文献
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A series of β-amino alcohols derivatives were synthesized from (R)-2-amino-1-butanol and (S)-1,2-propanediol, and they have been used as organocatalaysts in the racemic ring opening of epoxide in good yields with high enantiomeric excess (up to 97%). 相似文献
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Three novcl C2-symmetic macrocycles containing pyridyl units have been prepared by the cyclic condensation of chiral diamide intermediates with 2,6-pyridinedicarbonyl dichloride in highly diluted solution at room temperature. 相似文献
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Abstract: As part of our studies directed toward the development of new HIV protease inhibitors, a new type of C2-symmetric molecule having a dimeric hydroxyethylene isosteric moiety is synthesised by Cu(II)-mediated dimerisation of the sodium enolate of an amino acid-derived methylketo copound. 相似文献
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Taisei Taniguchi Dr. Yuji Nishii Prof. Dr. Tadashi Mori Prof. Dr. Ken-ichi Nakayama Prof. Dr. Masahiro Miura 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(26):7356-7361
Treatment of 11,12-bis(1,1’-biphenyl-3-yl or 6-phenylpyridin-2-yl)-substituted 11,12-dihydro-indolo[2,3-a]carbazole with an oxidizing system of Pd(II)/Ag(I) induced effective double dehydrogenative cyclization to afford the corresponding π-extended azahelicenes. The optical resolutions were readily achieved by a preparative chiral HPLC. It was found that the pyridopyrrolo-carbazole-based azahelicene that contains four nitrogen atoms exhibits ca. 6 times larger dissymmetry factors both in circularly dichroism (CD) and circularly polarized luminescence (CPL), |gCD| and |gCPL| values being 1.1×10−2 and 4.4×10−3, respectively, as compared with the parent indolocarbazole-based azahelicene. Theoretical calculations at the RI-CC2 level were employed to rationalize the observed enhanced chiroptical responses. The (chir)optical properties of the former helicene was further tuned by a protonation leading to remarkable red-shift with a considerable enhancement of the |gCPL| value. 相似文献
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Peng Fei YAN Wen Bin SUN Guang Ming LI Chun Hong NIE Zheng Yu YUE 《中国化学快报》2006,17(10):1297-1300
The finding of new chiral metal catalysts for enantioselective reactions has been the subject of many investigations in recent years1,2. Metal-catalyzed, especially transition metal-catalyzed asymmetric hydrogenation of prochiral ketones was an efficient … 相似文献
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Yannick Linne Axel Schönwald Sebastian Weißbach Prof. Dr. Markus Kalesse 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(36):7998-8002
anti-Configured 1,3-dimethyl deoxypropionate motifs are important sub structures in natural products. Herein, we describe a bidirectional approach for the rapid construction of natural products featuring such motifs by using C2-symmetrical 1,3-bis(boronic esters). As for its application in convergent syntheses it was important to establish a selective mono-Zweifel olefination we describe the scope and limitations by using different 1,3-bis(boronic esters) and nucleophiles. This protocol takes advantage of the combination of the Hoppe–Matteson–Zweifel chemistry, which was elegantly put into practice by Aggarwal et al. In order to show its applicability the total syntheses of two natural products, serricornin and (+)-invictolide, were performed. 相似文献
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tert-Butyl-substituted diphospha[2]ferrocenophane was used as a stereochemically confined diphosphane to investigate the addition of various dichalcoganes (R2Ch2; Ch = S, Se, Te and R = Me, Ph). Bischalcogenophosphinous acid esters bearing four soft donor sides were obtained as a mixture of rac and meso diastereomers and characterized by means of multinuclear NMR and X-ray analysis. The coordination chemistry of multidentate ligand 3b was explored toward d10 coinage metal centers (Cu(I), Ag(I), and Au(I)), yielding various bimetallic complexes. 相似文献