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Issue 10, 2011
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Recyclable copper catalysts based on imidazolium-tagged C2-symmetric bis(oxazoline) and their application in D–A reactions in ionic liquids

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Abstract

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.

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

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Supplementary files

Article information


Submitted
04 Jul 2011
Accepted
09 Aug 2011
First published
06 Sep 2011

Green Chem., 2011,13, 2963-2971
Article type
Paper

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

Z. Zhou, Z. Li, X. Hao, X. Dong, X. Li, L. Dai, Y. Liu, J. Zhang, H. Huang, X. Li and J. Wang, Green Chem., 2011, 13, 2963
DOI: 10.1039/C1GC15788D

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