AbstractSynthetic 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. J. Heterocyclic Chem., (2011).
New 1-Substituted 4-Cinnamoyl-5- hydroxypyrazoles and Precursors thereof: Synthesis, Ring Closure Reactions and NMR-Spectroscopic Investigations
作者:Wolfgang Holzer、Ingrid Krca
DOI:10.3987/com-03-9857
日期:——
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.