SYNTHESIS, REACTION, THEORETICAL CALCULATION, NMR-STUDY AND X-RAY CRYSTAL-STRUCTURE OF 1-SUBSTITUTED AND 1-UNSUBSTITUTED 1H-PYRAZOL-5(2H)-ONES

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 hydrazon es were isolated, while in others the products were obtained in one st ep. 1-Unsubstituted 4-alkoxy-, 4-alkylthio-, and 4-aryloxy-1H-pyrazol- 5-(2H)-ones were produced by methanolysis of the corresponding 1-subst ituted derivatives under reflux. Some of these compounds were studied by molecular mechanics calculations, as well as deuterium induced shif ts (DIS) on C-13 chemical shires, and tentative conclusion was drawn a bout their tautomerism and conformations. X-Ray crystal structure dete rminations of carbonyl)-3-methyl-4-methoxy-1H-pyrazol-5-(2H)-one 4e an d 3-methyl-4-methoxy-1H-pyrazol-5-(2H)-one 5a demonstrated that both m olecules exist in the crystal exclusively in the HN-CO tautomeric form . Some previously reported structural assignments in some pyrazolones and hydroxypyrazoles were corrected. (C) 1997 Published by Elsevier Sc ience Ltd.