PEI–silica catalysis under microwave irradiation: solvent-free condensation of dehydroacetic acid with aromatic and heteroaromatic aldehydes

Dehydroacetic acid (DHA; 3-acetyl-4-hydroxy-6-methyl-2H-pyran-2-one) is a versatile synthon, and its derivatives exhibit a variety of biological activities. Building on our previous study showing that polyethyleneimine supported on silica (PEI–silica) is an effective catalyst for Knoevenagel condensations, we report here the condensation of DHA with aromatic and heteroaromatic aldehydes under microwave irradiation in the absence of a solvent. Under these short, energy-efficient conditions, the protocol is in ligne with green chemistry principles, and the solid PEI–silica catalyst can be easily recovered and recycled. Compared with a wide range of Brønsted and Lewis acid–base catalysts, the PEI–silica ranks among the most active, consistent with acid–base cooperativity between the polyethylenimine and silica components. The resulting (E)-4-hydroxy-6-methyl-3-(arylacryloyl)-2H-pyran-2-ones were obtained in good to excellent yields and characterized by ¹H/¹³C NMR, IR, and mass spectrometry.

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