Synthesis of Pyran-Annulated Heterocyclic Systems Catalyzed by Theophylline as a Green and Bio-Based Catalyst

A green synthetic route to the convenient preparation of tetrahydrobenzo[b]pyran, pyrano[2,3-d]pyrimidinone and dihydropyrano[2,3-c]pyrazole scaffolds have been developed using theophylline as a green and bio-based catalyst via tandem Knoevenagel-Michael cyclocondensation reaction in aqueous/ethanol media. All reactions are completed in short period of times and the products are obtained in excellent yields. The salient features of this environmentally friendly approach are green and bio-based catalyst, straightforward work-up with no column chromatographic separation, one-pot procedures, economical and clean synthesis, avoidance of toxic organic solvents and high atom-economy.