Evans, N. A. published the artcileTautomerism in the 5-pyrazolone series. 1(H)-5-Pyrazolones and indazolones, Application of 5-Phenyl-1H-pyrazol-3(2H)-one, the main research area is .
Preparation according to Wolff (W. and Schreiner, CA 2, 1451) gave the tautomer MeC(:NNHCMe:CHCO2Et)CH2CO2Et (I), m. 46°; the ester (II), m.. 188°; the lactone (III, R = H) (IV), m. 250°; and III (R = Ac) (V), m. 184°. AcCH2CO2Et(0.01 mol) and 0.01 mol H2NNHAc refluxed 3 h. in alc. gave 55% MeC(:NNHAc)CH2CO2Et (VI), m. 82°. The assigned structure for I was deduced from the N.M.R. spectrum. I was recovered unchanged from C5H5N. I readily rearranged to II and its structure was unambiguously formulated on the basis of the N.M.R. and ir data. The formulation for III followed from the N.M.R. spectrum. IV showed a broad band at νNH 3225 cm.-1 (KCl) removed by acetylation to give V, νCO 1739 cm.-1 (KCl). Spectral data in solution and solid state were consistent with the formulation of II in the enolic form of the pyrazoline ring and suggested that other simpler 1(H)-5-pyrazolones might be formulated better as the enol rather than as the lactam. It was shown that II, 1(H)-3-methyl-5-pyrazolone (VII) (R = R2, R3 = H, R1, = Me) (VIII), m. 217°, VII (R = R2 = R3 = H, R1 = Ph) (IX), m. 236°, and related compounds exist in the enolic form in the solid state and predominantly so in solvents in which they are soluble VIII (3 g.) in 10 mL. C5H5N heated on a steam bath and stirred with dropwise addition of 3.1 g. AC2O, the solution heated 10 min. and diluted with H2O yielded 70% N-Ac derivative, m. 170-2°. VIII (1 g.) heated 1 h. on a steam bath in 5 mL. Ac2O and the product sublimed gave 80% yield of the diacetate (VII, R = R3 = Ac, R1 = Me, R2 = H), m. 38°. Spectral data obtained for VII (R = R3 = Bz, R1 = Me, R2 = H), m. 128°, supported the earlier formulations as 1-benzoyl-3-methyl-5-benzoyloxypyrazole. The isomeric acetates of IX were prepared according to the literature and the structures differentiated by the ir data confirmed the formulations previously proposed by Weissberger and Porter (CA 38, 972). Indazolone derivatives (X) were found to be represented exclusively by the enolized structure. Indazolone (X, R = R’ = H) (XI, 0.19 g.) and 0.2 g. p-MeC6H4SO2Cl refluxed 30 min. in 8 mL. C5H5N gave 0.17 g. X (R = H, R’ = p-MeC6H4SO2) (XII), m. 147°. XII refluxed 2 h. in Ac2O and the mixture kept 16 h. at 19° gave X (R = Ac, R’ = p-MeC6H4SO2) (XIII), m. 106°. C5H5N (10 mL.) containing 1 g. o-H2NNHC6H4CO2H and 1 g. p-MeC6H4SO2Cl refluxed 30 min. gave 0.73 g. α-(ο-carboxyphenyl)-β-tolylsulfonylhydrazine, m. 187° (decomposition), heated (0.17 g.) 2 h. in 6 mL. on a water bath to give 0.15 g. 1-acetyl-2-tolylsulfonylindazolone (XIV). The difference in the uv spectra between XII and XIII on the one hand and between XII and XIV on the other was a confirmation of the ir and chem. basis for determining their structures. XI methylated with 3-fold excess of CH2N2 in Et2O-MeOH at 0° 2 h. gave X (R = H, R’ = Me), m. 104°; Ac derivative m. 89° (petr. ether). The high frequencies found for CO groups in the ir spectra reflect a lack of conjugation with the π-electrons of the heterocyclic ring. The progressive movement to higher frequencies observed in the solution spectra of the 1-acetylspectra of the 1-acetylindazolones as the 3-substituent increases in electron withdrawing power (OMe < OAc < O3SC6H4Me-p) suggests that the N lone pair contributes to the π-electron system and that the acyl CO group reflecting the diminished conjugation approximates more to the state of a Me ketone modified by the direction bond to an atom of greater electronegativity. Tetrahedron published new progress about IR spectra. 27412-71-1 belongs to class pyrazoles-derivatives, name is 5-Phenyl-1H-pyrazol-3(2H)-one, and the molecular formula is C9H8N2O, Application of 5-Phenyl-1H-pyrazol-3(2H)-one.
Referemce:
Pyrazole – Wikipedia,
Pyrazoles – an overview | ScienceDirect Topics