An expedient four-component domino protocol for the regioselective synthesis of highly functionalized pyranopyrazoles and chromenopyrazoles via nitroketene-N,S-acetal chemistry under solvent-free condition

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

“…The structure of the compound 4a was conrmed by its melting point, IR, 1 H and 13 C NMR spectroscopies, and the data matched well with the reported data. [20][21][22][23][24] Encouraged by these results, we proceeded to optimize the reaction conditions. For this process, the model reaction was executed in the presence of different acid and base catalysts (10 mol%) in EtOH (4 mL) as well as without catalyst in EtOH with reux (Table 1, entries 2-6).…”

“…All the synthesized compounds were characterized by spectroscopic techniques including IR, 1 H and 13 C NMR spectroscopies and elemental analysis; the resulting data for several of the reported compounds are well-matched with the literature. [20][21][22][23][24] Further, the structure and stereochemistry of the compounds 4a (CCDC 1901104) and 6b (CCDC 1901105) were unambiguously conrmed by single-crystal X-ray diffraction analysis, and the ORTEP diagrams are shown in Fig. 2 and 3, respectively.…”

“…20) and piperidine, 21 whereas coumarin-fused 4H-pyran scaffolds were prepared using catalysts such as STA, 22 6,6 0 -thiobis(methylene)b-cyclodextrin dimer 23 and piperidine. 24 Regardless of the adequacy of these reported methods, each exhibits one or more shortcomings, such as the required usage of catalysts [20][21][22][23][24] or solvents 20,24 and prolonged reaction time. 20,24 Therefore, there still remains a scope of improvement of the synthetic strategy to access such important fused 4H-pyrans.…”

NitroketeneN,S-acetals: synergistic building blocks for the synthesis of heterocycles

“…Next, Jayabal and Paramasivan explored the combination of 2-hydroxybenzaldehydes 84 and NMSM 9 for the synthesis of pyrazole-containing chromene 85a rings under SF conditions. 60 The one-pot four-component reaction was carried out by heating the mixture of all the starting components at 120 C in the presence of 25 mol% piperidine for 1 h. They also used the aromatic aldehydes 38 instead of 2-hydroxybenzaldehydes under similar conditions, and the pyrazole-fused chromenes 85b were obtained (Scheme 27).…”

Ag/Tio2 Nano Thin Films Catalyzed Efficient Synthesis of 6-Amino-4-Aryl-3-Methyl-1,4-Dihydropyrano[2,3-C] Pyrazole-5-Carbonitriles At Green Conditions

“…Moreover, dihydropyrano [2,3-c]pyrazoles exhibit molluscicidal activity 29 , and has been identified as a screening kit for Chk1 kinase inhibitor 30 . Because of the importance of these compounds, a number of methods have been reported for their synthesis in the presence of various catalysts such as ionic liquids 31,32 , organic bases [33][34][35][36] , amberlyst 37 , glycine 38 , per-6-amino-b-cyclodextrin 39 , and iodine 40 .…”