Catalyst-free green synthesis of dihydropyrano[2,3-c]pyrazole scaffolds assisted by ethylene glycol (E-G) as a reusable and biodegradable solvent medium

We revealed a catalyst-free, green and rapid one-pot four-component tandem strategy for the preparation of dihydropyrano[2,3-c]pyrazoles – a biologically significant scaffold – via Knoevenagel-Michael cyclocondensation based on green chemistry principles. Highlights of the current practice are the application of non-hazardous reaction circumstances, catalyst-free, operational simplicity, use of inexpensive initiating substances, isolation of pure product via easy filtration thus preventing the requirement for column chromatography, metal-free, excellent yields, time-saving aspects of the reaction. However, the green ethylene glycol (E-G) can be recycled at least six times with no considerable reduction in activity making it greatly advantageous in addressing the industrial requirements and environmental worries.

Graphic Abstract

: The catalyst-free and environmentally friendly synthesis of dihydropyrano[2,3-c]pyrazole scaffolds are reported via ethylene glycol (E-G) as a green, reusable and biodegradable promoting media via tandem Knoevenagel-Michael cyclocondensation reaction of ethyl acetoacetate, hydrazine hydrate/phenylhydrazine, aromatic/aliphatic aldehydes and malononitrile provided the anticipated products in outstanding yields and short reaction times which might solve some cost problems in industry