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A catalyst- and solvent-free protocol for the sustainable synthesis of fused 4H-pyran derivatives
- Khan, Md. Musawwer, Shareef, Sumbulunnisan, Saigal,, Sahoo, Subash C.
- RSC advances 2019 v.9 no.45 pp. 26393-26401
- 4-hydroxycoumarin, X-ray diffraction, aldehydes, catalysts, chemical reactions, cost effectiveness, pyrazoles, solvents, spectroscopy, toxicity
- An efficient and cost-effective method was developed for the synthesis of two kinds of fused 4H-pyran derivatives, namely, dihydropyrano[2,3-c]pyrazole 4 and pyrano[3,2-c]chromenone 6. The reactions of 3-methyl-1-phenyl-5-pyrazolone/4-hydroxycoumarin with aromatic aldehydes and (E)-N-methyl-1-(methylthio)-2-nitroethenamine (NMSM), involving the Knoevenagel, Michael-addition, O-cyclization and elimination reactions under thermal heating, afforded the desired products. The synthesized compounds were characterized by standard spectroscopic techniques. Further, the structures of pyrazole-fused 4H-pyran 4a and coumarin-fused 4H-pyran 6b were confirmed by single-crystal XRD analysis. The short reaction time, good-to-excellent yields, elimination of the use of expensive, metallic and toxic catalysts or hazardous organic solvents and high atom-economy are some noteworthy features of this protocol.