An efficient catalyst- and solvent-free method for the synthesis of medicinally important dihydropyrano[2,3-c]pyrazole derivatives using ball milling technique

Dihydropyrano[2,3-c]pyrazole annulated heterocyclic compounds with diverse substituents on the 4H-pyran ring were efficiently prepared via a one-pot and four-component reaction of ethyl acetoacetate, hydrazine hydrate, aromatic aldehyde, and malononitrile. The procedure proceeds without utilization of any catalyst or solvent using ball milling technique at ambient temperature to afford desired medicinally important dihydropyrano[2,3-c]pyrazole derivatives. This protocol offers several advantages such as avoiding the use of any toxic and hazardous catalyst or solvent, mild reaction conditions, high to quantitative yields of products, low cost, and straightforward work-up.