Solvent Free Microwave-Assisted Knoevenagel Condensation of Dehydroacetic Acid with Benzaldehyde Derivatives

Abstract

Synthesis of 3-cinnamoyl-4-hydroxy-6-methyl-2-pyrone (3) series via Knoevenagel condensation of dehydroacetic acid with benzaldehyde derivatives was dramatically enhanced with respect to conventional heating (CV) by a specific microwave effect when the reaction was performed, under solvent-free conditions, in a microwave reactor. Excellent isolated yields (up to 90 %) were attained within short reaction times (typically 2 to 10 min). Knoevenagel condensation assisted by solvent free microwave procedure (SFMW) was better than conventional procedure in terms of energy saving (20-fold reduction), rapidity (60- fold reduction), yield and cleanliness. Synthesized compounds wera characterized by IR, ¹H and ¹³C NMR spectroscopy.