Recyclable copper catalysts based on imidazolium-tagged C2-symmetric bis(oxazoline) and their application in D―A reactions in ionic liquids

Functional imidazolium ionic liquids have been developed as a new class of versatile catalysts. C2-symmetric and unsymmetric imidazolium-tagged bis(oxazoline) ligands were prepared, and the anions of the ligands were altered by ion-exchange reactions. The catalysts based on the new ligands and Cu(OT...

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Bibliographic Details
Published in:Green chemistry : an international journal and green chemistry resource : GC 2011-01, Vol.13 (10), p.2963-2971
Main Authors: ZHOU, Zhi-Ming, LI, Zhi-Huai, WANG, Jin-Liang, HAO, Xiao-Yan, XIAO DONG, XIN LI, LI DAI, LIU, Ying-Qiang, JUN ZHANG, HUANG, Hai-Feng, XIA LI
Format: Article
Language:English
Subjects:
Alicyclic compounds
Alicyclic compounds, terpenoids, prostaglandins, steroids
Asymmetry
Catalysis
Catalysts
Catalysts: preparations and properties
Chemistry
Conversion
Exact sciences and technology
General and physical chemistry
Heterocyclic compounds
Heterocyclic compounds with n hetero atom and also o and/or s, se, te hetero atoms
Heterocyclic compounds with several n hetero atoms in the same ring, in separated rings or in fused rings
Ionic liquids
Ligands
Organic chemistry
Preparations and properties
Recycled
Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
Toxicity
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Summary:Functional imidazolium ionic liquids have been developed as a new class of versatile catalysts. C2-symmetric and unsymmetric imidazolium-tagged bis(oxazoline) ligands were prepared, and the anions of the ligands were altered by ion-exchange reactions. The catalysts based on the new ligands and Cu(OTf)2 were applied in asymmetric Diels-Alder reactions between N-acryloyl/N-crotonoyloxazolidinones 15 and 1,3-cyclohexandiene/cyclopentadiene 16 in different ionic liquids and in dichloromethane (DCM). The catalysts achieved a high level of activity and enantioselectivity, as well as good recyclability: cycloadduct (S)-17ab was attained at 98% conversion and 97% ee in [Bmim]NTf2. Moreover, the catalyst could be recycled 20 times without an obvious loss of activity or enantioselectivity. By comparison, we deduced that the C2 symmetry of the new ligands was crucial for obtaining high ee values. Toxicity studies of the ligands were performed for the first time.
ISSN:1463-9262
1463-9270
DOI:10.1039/c1gc15788d