Four-Component Synthesis of Dihydropyrano[2,3-c]pyrazole Scaffolds Using Glycerol as Green Reaction Media under Catalyst-Free Conditions.

A catalyst-free and convenient synthetic route to the green one-pot preparation of dihydropyrano[2,3-c]pyrazole scaffolds via four-condensation domino reaction of tandem Knoevenagel-Michael cyclocondensation reaction of ethyl acetoacetate, hydrazine hydrate, aryl aldehyde derivatives and malononitrile in glycerol as a reusable and biodegradable promoting media has been described. All reactions are completed in short period of times and the products are obtained in excellent yields. The salient features of this green and expedient approach are catalyst-free conditions, a green and biodegradable reaction medium, excellent yields, straightforward work-up with no column chromatographic separation, avoidance of toxic organic solvents and reagents, one-pot procedure, simplicity of operation and high atom-economy. Also, the glycerol was highly stable and could be reused in four successive runs with no significant structural change and loss of activity which makes it highly beneficial to address the industrial needs and environmental concerns. [ABSTRACT FROM AUTHOR]