Synthesis, reaction, theoretical calculation, NMR study and X-ray crystal structure of 1-substituted and 1-unsubstituted 1H-pyrazol-5(2H)-ones

Article abstract of DOI:10.1016/S0040-4020(97)00217-2

1-Substituted 4-alkoxy-, 4-alkylthio-, and 4-aryloxy-1H-pyrazol-5(2H)-ones have been prepared by the reaction of conjugated azoalkenes with alcohols, thiols, and phenols. In some cases the intermediate hydrazones were isolated, while in others the products were obtained in one step. 1-Unsubstituted 4-alkoxy-, 4-alkylthio-, and 4-aryloxy-1H-pyrazol-5(2H)-ones were produced by methanolysis of the corresponding 1-substituted derivatives under reflux. Some of these compounds were studied by molecular mechanics calculations, as well as deuterium induced shifts (DIS) on ¹³C chemical shifts, and tentative conclusion was drawn about their tautomerism and conformations. X-Ray crystal structure determinations of 1-(aminocarbonyl)-3-methyl- 4-methoxy-1H-pyrazol-5(2H)-one 4e and 3-methyl-4-methoxy-1H-pyrazol-5(2H)-one 5a demonstrated that both molecules exist in the crystal exclusively in the HN-CO tautomeric form. Some previously reported structural assignments in some pyrazolones and hydroxypyrazoles were corrected.