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. 2019 Aug 22;9(45):26393-26401.
doi: 10.1039/c9ra04370e. eCollection 2019 Aug 19.

A catalyst- and solvent-free protocol for the sustainable synthesis of fused 4 H-pyran derivatives

Md Musawwer Khan  1 , Sumbulunnisan Shareef  1 , Saigal  1 , Subash C Sahoo  2
Affiliations

A catalyst- and solvent-free protocol for the sustainable synthesis of fused 4 H-pyran derivatives

Md Musawwer Khan et al. RSC Adv. .

Abstract

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.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. Some representative examples of biologically active fused 4H-pyrans.
Scheme 1
Scheme 1. Synthesis of pyrazole- and coumarin-fused 4H-pyrans under neat conditions.
Fig. 2
Fig. 2. ORTEP representation of compound 4a (CCDC 1901104).
Fig. 3
Fig. 3. ORTEP representation of compound 6b (CCDC 1901105).
Scheme 2
Scheme 2. Plausible mechanism for the synthesis of the pyrazole- and coumarin-fused 4H-pyrans.
See this image and copyright information in PMC

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