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The phosphine oxide-linked bis(oxazoline) ligands were designed and synthesized in two ways. One is the coupling of Grignard reagent derived from 2-(2-bromophenyl)oxazoline with phenylphosphonic dichloride, another route is the condensation of bis(2-formylphenyl)(phenyl)phosphine oxide with chiral amino alcohols followed by NBS oxidation. These new bis(oxazoline) ligands were applied in Pd-catalyzed asymmetric allylic alkylation reactions and good yields and enantioselectivities were obtained with diphenyl substituted ligand (up to 95% ee). 相似文献
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The electronic effect of diphenylamine-linked bis(oxazoline) ligands was tuned through introduction of electron-withdrawing
bromo and nitro substituents onto the 4 and 4′ position. The variation of the NH bond acidity was determined by the different
chemical shifts of NH. The catalytic activity and enantioselectivity of the modified ligands were tested in the asymmetric
Friedel-Crafts alkylation of indole with β-nitrostyrene. The effect of ligand skeleton rigidity was also investigated through
the synthesis of iminodibenzyl-linked bis(oxazoline) ligands and evaluation of their catalytic activity in Friedel-Crafts
alkylation. 相似文献
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《Tetrahedron: Asymmetry》1999,10(16):3095-3098
The use of sterically congested C2-symmetrical bis(oxazoline) ligands with methylene and ethylene spacers between the oxazoline rings results in the reversal of the enantioselection for aldol reactions catalyzed by bis(oxazoline)–Cu(II) complexes. 相似文献
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Chollet G Guillerez MG Schulz E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(3):992-1000
A new method for recycling chiral bis(oxazoline)-copper complexes is described based on the formation of charge-transfer complexes, their subsequent precipitation, and reuse after addition of new substrates. The conditions to perform this procedure were optimized in the presence of three bis(oxazoline)-based ligands. When associated with copper salts, these ligands efficiently catalyzed the Diels-Alder reaction between cyclopentadiene and alpha,beta-unsaturated acyloxazolidinones. These catalysts were successfully recycled up to ten times while maintaining their high activities and enantioselectivities. 相似文献
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Chiral bis(oxazoline) ligands have been applied in many enatioselective reactions. Recently, studies of the immobilization of bis(oxazoline) on both soluble and insoluble supports have been of great interest. Among the different methods to anchor the homogeneous catalysts, a soluble, polymer-supported catalyst usually achieves higher stereoselectivity and activity because the catalysis can be separated and recycled via simple methods such as solvent precipitation. Dendrimers are highly branche… 相似文献
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A series of novel chiral C2-symmetric bis (oxazoline) ligands have been synthesized.The copper and magnesium complexes,prepared in situ from copper(Ⅱ)-triflate of magnesium triflate with the new enantiopure oxazoline ligands,were evaluated as chiral catalysts in the enantioselective Diels-Alder reaction of cyclopentadiene with N-crotenoyl-oxazolidin-2-one.Primary results showed that diastereoselectivity up to 94% and enantioselectivity up to 68% ee for endo products were observed respectively with these ligands. 相似文献
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Michael Seitz 《Tetrahedron》2006,62(42):9973-9980
Highly modular N,Y,Z,Y,N-ligands (Y=N, O, S; Z=N, NO, OH, OMe) have been prepared using bis(oxazoline) building blocks either as nucleophiles or as electrophiles in coupling reactions with central aromatic units. This way, a great variety of pentadentate bis(oxazoline) ligands in diastereo- and enantiomerically pure form become readily available, which are useful for the construction of helical metal complexes with predetermined chirality. 相似文献
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A series of new C(2)-symmetric fluoren-9-ylidene malonate-derived bis(oxazoline) ligands were synthesized from fluoren-9-ylidene malonate and enantiomerically pure amino alcohols via a convenient route. Their asymmetric catalytic properties in the Friedel-Crafts reactions of indoles with arylidene malonates were evaluated, and the Cu(OTf)2 complex of a fluoren-9-ylidene malonate-derived bis(oxazoline) bearing a phenyl group showed moderate to good enantioselectivity (up to 88% ee). 相似文献
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Fraile JM García JI Gissibl A Mayoral JA Pires E Reiser O Roldán M Villalba I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(31):8830-8839
A thorough experimental and theoretical study of the enantioselective cyclopropanation of alkenes catalyzed by chiral bis(oxazoline)- and azabis(oxazoline)-copper complexes, which comprise a new family of ligands that lack C2 symmetry, has been conducted. Surprisingly high enantioselectivities were observed with some of these ligands, which were rationalized on the basis of molecular modeling studies. The course of the asymmetric induction in connection with ligand symmetry and the implications for supported enantioselective catalysts are discussed. 相似文献
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《Tetrahedron letters》2004,45(36):6765-6768
Azabis(oxazoline)-Cu complexes are more stable than their analogues based on bis(oxazoline) ligands. This increased stability leads to improved recoverability (up to eight times) when these systems are used in an ionic liquid medium. The solution of the chiral catalyst can even be reused in different enantioselective cyclopropanation reactions and still lead to high enantiomeric excess (>90%). 相似文献
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Heteroleptic [Bis(oxazoline)](dipyrrinato)zinc(II) Complexes: Bright and Circularly Polarized Luminescence from an Originally Achiral Dipyrrinato Ligand 下载免费PDF全文
Dr. Julius F. Kögel Dr. Shinpei Kusaka Dr. Ryota Sakamoto Toshiki Iwashima Mizuho Tsuchiya Ryojun Toyoda Ryota Matsuoka Dr. Takamasa Tsukamoto Dr. Junpei Yuasa Prof. Dr. Yasutaka Kitagawa Prof. Dr. Tsuyoshi Kawai Prof. Dr. Hiroshi Nishihara 《Angewandte Chemie (International ed. in English)》2016,55(4):1377-1381
Heteroleptic zinc(II) complexes synthesized using achiral dipyrrinato and chiral bis(oxazoline) ligands show bright fluorescence with quantum efficiencies of up to 0.70. The fluorescence originates from the 1π–π* photoexcited state localized exclusively on the dipyrrinato ligand. Furthermore, the luminescence is circularly polarized despite the achirality of the dipyrrinato ligand. Single‐crystal X‐ray structure analysis discloses that the chiral bis(oxazoline) ligand undergoes intramolecular π–π stacking with the dipyrrinato ligand, inducing axial chirality in the dipyrrinato moiety. 相似文献
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We report the good to high-yielding three-step synthesis of non-symmetrical bis(oxazoline)-containing ligands possessing an N-thienylaniline unit. The convergent synthesis employed a palladium-catalysed aryl amination of 2-(2'-bromothiophene)nitrile as the key step, with sixteen ligands prepared in total. These ligands were subsequently applied in the chromium-catalysed enantioselective Nozaki-Hiyama-Kishi allylation of benzaldehyde with an optimal enantioselectivity of 73%. 相似文献
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Kharasch and Sosnovsky reported the allylic oxidation of alkenes to give racemic allylic benzoates. This could be achieved efficiently using a tert-butyl perester as the oxidant, in the presence of a copper or cobalt salt. The use of C(2)-symmetric bis(oxazoline) ligands in the presence of copper(I) triflate with cyclic olefinic substrates gave the first synthetically useful asymmetric variant. The enantioselective control was good (up to 84 % ee) although yields were variable. In all cases the facial preference of the newly formed C-O bond was the same giving an S configuration at the allylic stereocenter. Lower stereocontrol was observed for large-ring alkenes and substantially reduced enantioselectivities were found with open-chain alkenes. This reaction has been further screened using a variety bis(oxazoline) and proline-derived ligands, which give a direct correlation between the chirality of the ligand and the enantioselectivity obtained. Individual substrates were found to be extremely sensitive to both the ligand structure and copper salt used as well as the presence of additives such as zinc, hydrazine, and molecular sieves. 相似文献
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Benaglia M Benincori T Mussini P Pilati T Rizzo S Sannicolò F 《The Journal of organic chemistry》2005,70(19):7488-7495
[structure: see text] The role played by the electronic properties and the steric features of bis(oxazoline) ligands in the Cu(I)-catalyzed cyclopropanation of styrene effected with ethyl diazoacetate was investigated. Two pairs of new bis(oxazolines) displaying flexible and atropisomeric 3,3'-bithiophene backbones were synthesized and structurally and electronically characterized. For the first time, the electrochemical oxidative potential was used as a reliable index of the electronic density on the nitrogen atom of the chelating groups of new and, for comparative purposes, of already known bis(oxazolines). The Cu(I) complexes of the new ligands were prepared, and their enantioselection ability and catalytic efficiency were tested. This investigation suggests that steric factors and catalyst geometrical features are clearly more important than any consideration of the electronic properties of the chiral ligands. 相似文献
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A series of novel C2-symmetrical chiral bis(oxazoline) and bis(thiazoline) ligands containing noncyclic crown ether type was synthesized. Their
structures were determined by IR spectra, 1H nuclear magnetic resonance (NMR), 13C NMR, and elemental analysis. The copper complexes of the above ligands were used in catalytic asymmetrical Henry reactions.
Enantioselectivities up to 33% were observed.
Translated from HuaXue TongBao, 2005, (2) (in Chinese) 相似文献
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《Tetrahedron: Asymmetry》2014,25(10-11):833-837
The use of ionic liquid phases to immobilise dicopper complexes of ditopic chiral ligands bearing bis(oxazoline) moieties has been explored in the enantioselective cyclopropanation reaction of styrene with ethyl diazoacetate. The recoverability of these catalytic phases has been studied using different ionic liquids and ligands. The origin of the ionic liquid is determinant both for the catalytic results and the reusability of the system. 相似文献