Acylation of coumarins in the presence of trifluoroacetic acid.

In recent months a method has been developed for the acylation of 4-pyrones by acyl halides in the presence of trifluoroacetic acid as the solvent.1 2 This method of acylation and bis-acylation is now extended to the 2-pyrones as typified in coumarin and 2-thiocoumarin.3 In addition to the new application of the reaction described above the ketones as produced are characterized by their malononitrile derivatives. The condensation of malononitrile has been shown previously4 to take place with the 4-pyrone carbonyl and any ketonic carbonyl in a compound; however, the reagent will not react with the carbonyl of a 2-pyrone. This contribution introduces a new class of derivative of ketonic