Facile synthesis of new pyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidin-5(1H)-ones via the tandem intramolecular Pinner–Dimroth rearrangement and their antibacterial evaluation

Some new 7-alkyl-4,6-dihydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidin-5(1H)-ones were prepared through heterocyclization of 6-amino-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles with aliphatic carboxylic acids in the presence of phosphoryl chloride under reflux in high yields. The suggested mechanism involves a tandem intramolecular Pinner–Dimroth rearrangement. The products were characterized on the basis of FT-IR, 1H NMR, and 13C NMR spectral and microanalytical data and evaluated for their antibacterial activity against Gram-positive bacteria (Staphylococcus aureus and Staphylococcus epidermidis) and Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) using the disk diffusion method.