共查询到19条相似文献,搜索用时 390 毫秒
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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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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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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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[Structure: see text] Simple bis(oxazoline) ligands, especially azabis(oxazolines), can catalyze the copper-catalyzed addition of indoles to benzylidene malonates in up to >99% ee, provided that excess of chiral ligand is avoided. The paradigm followed in many asymmetric catalyses that an excess of chiral ligand with respect to the metal should improve enantioselectivity because a background reaction by free metal is suppressed, is not applicable here, which might call for revisiting some of the many copper(II)-bis(oxazoline)-catalyzed processes known. 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
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[reaction: see text] C(2)-symmetric tridentate bis(oxazoline) and bis(thiazoline) ligands with a diphenylamine backbone have been investigated in the catalytic asymmetric Henry reaction of alpha-keto esters with different Lewis acids. Their Cu(OTf)(2) complexes furnished S enantiomers, while Et(2)Zn complexes afforded R enantiomers, both of them with higher enantioselectivities (up to 85% ee). Reversal of enantioselectivity in asymmetric Henry reactions was achieved with the same chiral ligand by changing the Lewis acid center from Cu(II) to Zn(II). The results show that the NH group in C(2)-symmetric tridentate chiral ligands plays a very important role in controlling both the yields and enantiofacial selectivity of the Henry products. 相似文献
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《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(6):1532-1536
2‐Pyridylsulfone‐ and fluoroalkylated group‐activated olefins underwent highly efficient diastereo‐ and enantioselective 1,3‐dipolar cycloadditions across various aromatic and aliphatic nitrones in the presence of a chiral NiII/bis(oxazoline) catalyst. The process was tuned by 4 Å molecular sieves, chiral bis(oxazoline) ligands, reaction solvents, and temperature. A wide array of optically pure fluoroalkylated isoxazolidines were obtained, thus facilitating the asymmetric synthesis of an enantioenriched α‐trifluoromethylated γ‐amino alcohol in gram‐scale and a trifluoromethylated derivative of 1,3‐oxazinan‐2‐one with potential pharmaceutical interest. A stereochemical model, based on the absolute configuration of one adduct and some control experiments, was postulated to account for the observed endo‐ and enantioselectivity. 相似文献
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A catalytic enantioselective ring expansion of monoactivated methylenecyclopropanes (MCP) in the presence of N-tosyl aldimines was developed using a chiral bis(oxazoline) ligand-MgI2 complex. After evaluation of ligands and optimization of the reaction conditions, the reaction has been applied to a variety of aromatic and heteroaromatic aldimines providing the corresponding trans-C2,C3-disubstituted methylenepyrrolidines in generally good yields (greater than 52%) and up to 86% ee. [reaction: see text]. 相似文献