New 1-substituted 4-cinnamoyl-5-hydroxypyrazoles and precursors thereof: Synthesis, ring closure reactions and NMR-spectroscopic investigations
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.
Holzer, Wolfgang,Krca, Ingrid
p. 2323 - 2342
(2007/10/03)
Pyrazoles. 5. Novel Pyrazole Analogues of Flavanone, Flavone and Flavane
The synthesis of the new pyranopyrazole derivatives 4, 5, and 7 starting from (E)-1-(1,3-dimethyl-5-hydroxy-4-pyrazolyl)-3-phenyl-2-propen-1-one (2) is reported.
Heinisch, Gottfried,Hollub, Christian,Holzer, Wolfgang
p. 1047 - 1050
(2007/10/02)
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