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.
在无溶剂条件下,通过在烤箱或微波炉中将
水杨 aldehydes 与
三氟乙酰乙酸乙酯进行 Knoevenagel 缔合反应,然后在
硅胶固定的
L-脯氨酸存在下进行分子内环化,成功合成了 2-羟基-2-(三
氟甲基)-2H-香豆烯-3-
羧酸酯。标题化合物的结构通过 IR、1H-NMR、13C-NMR、HRMS 和 X 射线单晶衍射进行表征。此处描述的改进方法经济、操作简便且环保。此外,催化剂可以方便地回收和重复使用,且活性无明显损失。