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Synthesis of Pyrazolyl‐2‐pyrazolines by Treatment of 3‐(3‐Aryl‐3‐oxopropenyl)chromen‐4‐ones with Hydrazine and Their Oxidation to Bis(pyrazoles)
Author(s) -
Lévai Albert,
Silva Artur M. S.,
Pinto Diana C. G. A.,
Cavaleiro José A. S.,
Alkorta Ibon,
Elguero José,
Jekö József
Publication year - 2004
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200400465
Subject(s) - tautomer , chemistry , pyrazole , hydrazine (antidepressant) , aryl , hydrate , acetic acid , medicinal chemistry , pyrazoline , chemical shift , organic chemistry , alkyl , chromatography
The synthesis of several 1‐acetyl‐3‐aryl‐5‐[3‐(2‐hydroxyphenyl)pyrazol‐4‐yl]‐2‐pyrazolines 3a − 3h has been accomplished by treatment of the 3‐(3‐aryl‐3‐oxopropenyl)chromen‐4‐ones 1a − h with hydrazine hydrate in hot acetic acid. The 1‐acetyl‐3‐aryl‐5‐(3‐chromonyl)‐2‐pyrazolines 2a − 2f were also obtained as by‐products. Oxidation of the 1‐acetyl‐4‐pyrazolyl‐2‐pyrazolines 3a − 3f with DDQ gave the 3(5)‐aryl‐5(3)‐[3‐(2‐hydroxyphenyl)pyrazol‐4‐yl]pyrazoles 5a − 5f . The oxidation of the 2‐pyrazoline rings was accompanied by N ‐deacylation. The reaction mechanisms of both transformations are discussed, the first one being supported by experimental results. The structures of all new derivatives were established by NMR and the evidence of prototropic tautomerism is carefully discussed. Theoretical calculations of energies and of the 1 H and 13 C NMR chemical shifts of the possible tautomeric forms of 5(3)‐[3‐(2‐hydroxyphenyl)pyrazol‐4‐yl]‐3(5)‐(4‐methoxyphenyl)pyrazole ( 5c ), by B3LYP and GIAO, showed that compounds of this type probably exist as mixtures of two tautomers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)