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;
18:11964-77. [PMID:
24077175 PMCID:
PMC6290574 DOI:
10.3390/molecules181011964]
[Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Revised: 09/07/2013] [Accepted: 09/11/2013] [Indexed: 11/17/2022] Open
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.
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