NaF-catalyzed efficient one-pot synthesis of dihydropyrano[2,3-c]pyrazoles under ultrasonic irradiation via MCR approach

Sodium fluoride was identified as an efficient catalyst for the preparation of series of dihydropyrano 2,3-c]pyrazoles (4a–l) by the three-component condensation of 3-Methyl-1-phenyl-2-pyrazoline-5-one (1), aromatic aldehydes (2) and malononitrile (3) in aqueous methanol at ambient temperature under ultrasonication. The cost and efficacy of the catalyst, mild reaction conditions, simple workup procedure, less reaction time and higher yields of the product with analytical purity keeping this protocol superior to the previously reported ones. Structures of all the compounds were in agreement with their spectroscopic data (¹H NMR, ¹³C NMR) and elemental (CHN) analyses.