635288-46-9Relevant academic research and scientific papers
Synthesis of some pyrano[2,3-c]pyrazoles
Pavlik, James W.,Ervithayasuporn, Vuthichai,Tantayanon, Supawan
scheme or table, p. 710 - 714 (2011/07/31)
Synthetic methods have been developed to prepare pyrano[2,3-c]pyrazoles with various substituents at ring positions 1, 3, and 6. The 1H- and 13C-NMR properties of these products and their precursors are presented and discussed.
On the tautomerism of pyrazolones: The geminal 2J[pyrazole C-4,H-3(5)] spin coupling constant as a diagnostic tool
Holzer, Wolfgang,Kautsch, Constanze,Laggner, Christian,Claramunt, Rosa M.,Pérez-Torralba, Marta,Alkorta, Ibon,Elguero, José
, p. 6791 - 6805 (2007/10/03)
The tautomerism of pyrazolones unsubstituted at position 3(5) has been investigated by 13C- and 1H NMR spectroscopic methods. Apart from chemical shift considerations and NOE effects the magnitude of the geminal 2J[pyrazole C-4,H3(5)] spin coupling constant permits the unambiguous differentiation between 1H-pyrazol-5-ol (OH) and 1,2-dihydro-3H-pyrazol-3-one (NH) forms. Whereas 1H-pyrazol-5-ols and 2,4-dihydro-3H-pyrazol-3-ones (CH-form) exhibit 2J values of approximately 9-11 Hz, in 1,2-dihydro-3H-pyrazol-3-ones this coupling constant is considerably reduced to 4-5 Hz. This can be mainly attributed to the removal of the lone-pair at pyrazole N-1 in the latter due to protonation or alkylation. According to the data obtained, 2-substituted 4-acyl-1,2-dihydro-3H-pyrazol-3- ones exist predominantly as pyrazol-5-ols in CDCl3 or benzene-d 6 solution, whereas in DMSO-d6 also minor amounts of NH tautomer may contribute to the tautomeric composition. 2,4-Dihydro-2-phenyl-3H- pyrazol-3-one (1-phenyl-2-pyrazolin-5-one) exists in benzene-d6 solely in the CH-form, in CDCl3 as a mixture of CH and OH-form, whereas in DMSO-d6 a fast equilibrium between OH and NH isomer (with the former far predominating) is probable. For 11 compounds, including neutral and protonated molecules, we have calculated at the B3LYP/6-311++G** level, the 2J(1H,13C) coupling constants which are in good agreement with those measured experimentally.
New 1-substituted 4-cinnamoyl-5-hydroxypyrazoles and precursors thereof: Synthesis, ring closure reactions and NMR-spectroscopic investigations
Holzer, Wolfgang,Krca, Ingrid
, p. 2323 - 2342 (2007/10/03)
Reaction of 1-substituted 5-hydroxy-1H-pyrazoles (pyrazolones) with trans-cinnamoyl chloride / calcium hydroxide in dioxane affords the corresponding 4-cinnamoyl-5-hydroxy-1H-pyrazoles. Cyclization of the latter into 5,6-dihydropyrano[2,3-c]pyrazol-4-ones proceeds in very low yields upon treatment with concentrated sulfuric acid. 1,6-Diphenyl-1H-pyrano[2,3-c]pyrazol-4-one was synthesized by reaction of of 4-acetyl-5-hydroxy-1-phenyl-1H-pyrazole with benzoyl chloride and lithium bis(trimethylsilyl)amide and subsequent cyclization of the thus obtained 1,3-diketone. NMR-spectroscopic investigations with the obtained 4-substituted 5-hydroxypyrazoles and their precursors regarding their tautomeric behavior in various solvents are presented.
