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Molecules 2013, 18(10), 11964-11977; doi:10.3390/molecules181011964
Article

An Efficient Solvent-Free Synthesis of 2-Hydroxy-2-(trifluoromethyl)-2H-chromenes Using Silica-Immobilized L-Proline

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School of Science, Henan Agricultural University, Zhengzhou 450002, China.
* Author to whom correspondence should be addressed.
Received: 15 July 2013 / Revised: 7 September 2013 / Accepted: 11 September 2013 / Published: 26 September 2013
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Abstract

An efficient synthesis of 2-hydroxy-2-(trifluoromethyl)-2H-chromene-3-carboxylates was carried out under solvent-free conditions in an oven or microwave oven via the Knoevenagel condensation of salicylaldehydes with ethyl trifluoroacetoacetate followed by intramolecular cyclization in the presence of silica-immobilized L-proline. The structures of the title compounds were characterized by IR, 1H-NMR, 13C-NMR, HRMS and X-ray single crystal diffraction. The improved method described herein is economical, easily-operated and environmentally friendly. Furthermore, the catalyst can be recovered conveniently and reused without obvious loss of activity.
Keywords: solvent-free; 2-hydroxy-2-(trifluoromethyl)-2H-chromene-3-carboxylates; synthesis; Knoevenagel condensation; silica-immobilized L-proline solvent-free; 2-hydroxy-2-(trifluoromethyl)-2H-chromene-3-carboxylates; synthesis; Knoevenagel condensation; silica-immobilized L-proline
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Xu, C.; Yang, G.; Wang, C.; Fan, S.; Xie, L.; Gao, Y. An Efficient Solvent-Free Synthesis of 2-Hydroxy-2-(trifluoromethyl)-2H-chromenes Using Silica-Immobilized L-Proline. Molecules 2013, 18, 11964-11977.

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