New 1-Substituted 4-Cinnamoyl-5- hydroxypyrazoles and Precursors thereof: Synthesis, Ring Closure Reactions and NMR-Spectroscopic Investigations
2003; Elsevier BV; Volume: 60; Issue: 10 Linguagem: Inglês
10.3987/com-03-9857
ISSN1881-0942
Autores Tópico(s)Synthesis and biological activity
ResumoReaction 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[2,3c]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.R 1 O O Ph (E)-PhCH=CHCOCl, Ca(OH) 2 , dioxane H 2 SO 4 concd a b c d e f R 1 Me Ph CH 2 Ph CH 2 Ph Me Ph R 3 H H H Me Me Me 1 2 3d-f 42% (2a), 61% (2b) 65% (2c), 58% (2d) 51% (2e) 10 , 69% (2f) 9 2% (3d) 2% (3e) 10 1% (3f) 9
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