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An Unequivocal Synthesis of 2-Aryl Substituted 3-Amino-2,4,5,7-tetrahydro-6H-pyrazolo[3,4-b]pyridin-6-ones
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The reaction between pyridones (1) and substituted hydrazines 4 can afford two different regioisomeric pyrazolo[3,4-b]pyridin - 6-ones 2 and 3 depending on the initial substitution of the methoxy group and the direction of the cyclization. In the case of phenylhydrazine 4 (R3 = Ph), we have clearly shown that the treatment of pyridones 1a-d with 4 (R3 = Ph) in MeOH at temperatures below 1408C yields, independently of the nature and position of the substituents present in the pyridone ring, the open intermediates 7a-d. When the reaction is carried at 1408C under microwave irradiation, the corresponding 2-aryl substituted pyrazolo[3,4-b]pyridines 3a-d are always formed. We have experimentally determined, using DSC techniques, the activation energies of the two steps involved in the formation of 3: a) substitution of the methoxy group present in pyridones 1 with phenylhydrazine 4 (R3 = Ph) to afford intermediates 7 and b) cyclization of intermediates 7 to yield pyrazolopyridines 3. The results obtained, 15 and 42 kcal·mol 1 respectively, are in agreement with the experimental findings.
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BOU-PETIT, Elisabeth, PICAS, Elsa, PUIGJANER VALLET, Ma. cristina, FONT BARDIA, Ma. mercedes, FERRER, Nabí, SEMPERE, Julià, PUIG DE LA BELLACASA, Raimon, BATLLORI, Xavier, TEIXIDÓ, Jordi, ESTRADA-TEJEDOR, Roger, RAMON Y CAJAL, Santiago, BORREL, José i.. An Unequivocal Synthesis of 2-Aryl Substituted 3-Amino-2,4,5,7-tetrahydro-6H-pyrazolo[3,4-b]pyridin-6-ones. _Chemistryselect_. 2017. Vol. 2, núm. 13, pàgs. 3668-3672. [consulta: 20 de gener de 2026]. ISSN: 2365-6549. [Disponible a: https://hdl.handle.net/2445/163391]