The First Synthesis of 4-Unsubstituted 3-(Trifluoroacetyl)coumarins by the Knoevenagel Condensation of Salicylaldehydes with Ethyl Trifluoroaceto­acetate Followed by Chromene-Coumarin Recyclization

A series of ethyl 6-substituted 2-hydroxy-2-(trifluoro-methyl)-2 H-chromene-3-carboxylates was obtained in good yields via the Knoevenagel condensation of salicylaldehydes with ethyl trifluoroacetoacetate in the presence of piperidinium acetate. The subsequent recyclization of these chromenes proceeds smoothly in refluxing chlorobenzene in the presence of P-toluenesulfonic acid affording previously unknown 3-(trifluoroacetyl)coumarins in moderate to good yields.