l-Proline catalyzed four-component one-pot synthesis of coumarin-containing dihydropyrano[2,3-c]pyrazoles under ultrasonic irradiation

A simple and convenient approach to the synthesis of coumarin-containing dihydropyrano[2,3-c]pyrazoles via four-component reaction of β-dicarbonyl compound, phenylhydrazine, aromatic aldehydes and malononitrile in EtOH catalyzed by l-proline under ultrasonic irradiation is described. The reaction gives the coumarin-containing dihydropyrano[2,3-c]pyrazoles in good to excellent yields at room temperature. This method provides several advantages, such as shorter reaction time, environmental friendliness, simple workup procedure and higher yields.

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