3- Pyrazolin-5-ones structure

A short time after the discovery of pyrazolin-5-ones Knorr809 proposed the 2-pyrazolin-5-one and the 3-pyrazolin-5-one structures on the basis of analyses, methods of preparation and reactions. These structures in the main approximate the correct ones and in some cases are correct. However, a large number of structures are theoretically possible for most pyrazolin-5-ones and in many cases no one structure can be said to fit completely. The tautomeric isomers (VII)-(XIII) are possible for unsubstituted pyrazolin-5-ones ... 

Chattaway and co-workers287-290,294 have synthesized a number of l-aryl-2-pyrazolin-4-ones which, as a rule, have been considered to have the 4-hydroxypyrazole structures. However, some of these must have the 2-pyrazolin-4-one structure due to disubstitution at C-5. Emerson and Beegle425 have synthesized some 2-pyrazolin-4-ones unsubstituted at N-l permitting more possibilities for isomerism. These will be discussed later. 

Acyl-, 4-alkoxycarbonyl- and 4-phenylazo-pyrazolin-5-ones present the possibility of a fourth tautomer with an exocyclic double bond and a chelated structure. The molecular structure of (138) has been determined by X-ray crystallography (Table 5). It was shown that the hydroxy group participates in an intramolecular hydrogen bond with the carbonyl oxygen atom of the ethoxycarbonyl group at position 4 (8OCSCII21). On the other hand, the fourth isomer is the most stable in 4-phenylazopyrazolones (139), a chelated phenyl-hydrazone structure. 

Muzolimine (710), a 1-substituted 2-pyrazolin-5-one derivative, is a highly active diuretic, differing from the structures of other diuretics since it contains neither a sulfonamide nor a carboxyl group. It has a saluretic effect similar to furosemide and acts in the proximal tubule and in the medullary portion of the ascending limb of the loop of Henle. Pharmacokinetic studies in dogs, healthy volunteers and in patients with renal insufficiency show that the compound is readily absorbed after oral administration (B-80MI40406). 

Substituted pyrazolin-5-ones have only three and -substituted pyrazolin-3-ones only two tautomers, since now the corresponding 19c and 19d structures are isomers. The calculations involved l-methylpyrazolin-5-one (PM3/6-3H-G, anions and cations), l-phenyl-3-methyl-2-pyrazolin-5-one (DFT, radical reactions) [97JPC(A)3769], and l-(2, 4 -dinitrophenyl)-3-methyl-2-pyrazolin-5-one [B3LYP/6-31G and the crystal structure (Section V,D,2)] (98NJC1421). 

Pyrazolin-5-one, 3-methyl-1 -phenyl-in colour photography, 5, 299 Pyrazolinones 13C NMR, 5, 193 H NMR, 5, 185, 187 colour couplers in colour photography in non-silver photography, 1, 384 IR spectra, 5, 200-202 structure, 5, 170 Pyrazolinones, dichloro-reactions with alkali, 5, 78 Pyrazolin-3-ones 1-substituted tautomerism, 5, 214 Pyrazolin-5-ones reactions... 

The organisms Pyricularia oryzae, which causes rice blast, and Helminthosporium oryzae, which causes brown leaf spot, can be controlled with complexes of the ligands 1-phenyl-3-methyl-4-nitroso-2-pyrazolin-5-one (36) and 3-methyl-4-nitroso-2-pyrazolin-5-one (37). The complexes were of the type ML Xj (L = 36, 37 X = C1-, Br, N03 ) or [ML2]Y2 (Y = C104 ). The former were assigned an octahedral or distorted octahedral structure and the latter are tetrahedral. The most active nickel complex was (38).92... 

The formation of pyrazoline derivatives 175 (but not dihydrotetrazolotria-zepines 173, as assumed earlier [53]) is brought about by the condensation of chalcones with diaminotetrazole 172 [128,129]. The structure of the compounds 175 is convincingly verified using X-rays. The mechanism of their formation implies a Dimrothe rearrangement for either the initial diamine or for one of the cyclocondensation intermediates (Scheme 4.51). 

Although it has not been possible to isolate the diazacyclopentadienone (47), indirect evidence for its involvement in this reaction has been obtained by trapping experiments. When an ether solution of 3,4-diphenyl-4-chloro-2-pyrazolin-5-one was treated with triethylamine in the presence of cyclopentadiene, an excellent yield was obtained of compound (51), which has been shown to be the Diels-Alder adduct. The unlikely possibility that (47) could have the alternative structure in which (51) acts as diene rather than dienophile can be excluded on the basis of the appearance of normal hydrazide carbonyl absorption. 

The tautomeric composition in solution of 4-(arylmethyl)isoxazol-5-one derivatives has been determined on the basis of H NMR and infrared (IR) data. The CH form was predominant in chloroform solution, while the NH and OH forms are more common in polar solvents and in the solid state <1996T1443>. 5-Hydroxy- and 5-amino-2-isoxazo-lines show different tautomeric forms in solution. The presence of cyclic hemiacetal or hemiaminal moieties in such molecules allows the easy cleavage of the C-5-0 bond to form linear structures. Subsequent intramolecular addition of nucleophiles to the C=N bond gives rise to cyclic structures. Compounds 20 exist, in the crystalline state, as the isoxazoline form A. In solution, a ring-ring tautomeric equilibrium was observed between the isoxazoline form A and the pyrazoline form C. The tautomeric ratio depended on steric factors and on the solvent used. The tautomeric equilibrium was established after several days (Scheme 2) <2000CHE722>. 

L-f/ireo-glycerol-l-yl)-pyrazoline-5-one (49) when its solution in alkali was acidified with acetic acid (50). The reaction was further extended to other bis(arylhydrazones) (51), The structure of the phenyl analogue (49) was established by oxidation to the known 3-carboxy-l-phenyl-4-phenylazopyrazolin-5-one (50). Later, on the basis of NMR data (39), the structure of this group of compounds was formulated as the hydra-zones (51). Acylation of 51 aflForded the tri-O-acylated derivatives (51), while periodate oxidation of 51 gave 3-formyl-l-aryl-4,5-pyrazoledione-... 

The development of new and improved dyes based on pyrazolinone structures has likewise led to modem developments of no inconsiderable magnitude. The use of tartrazine as an approved color for foodstuffs is of significance. The development of pyrazolinone dyes for use as magenta couplers and sensitizers in color photography and in metal chelate dye structures has established a renewed, modem interest in these dyes. The chelating characteristics, which will be of continuing theoretical structure interest in coordination chemistry, have been used in developing picrolonates (salts of 3-methyl-4-nitro-l-p-nitrophenyl-2-pyrazolin-5-one) of possible utility in analytical procedures. 

Pyrazolinones and pyrazolidinones are oxo derivatives of pyrazo-lines and pyrazolidines, respectively, and are so named in Chemical Abstracts at present. However, the usual method of naming in the earlier literature is the pyrazolone-pyrazolidone system. Although a large number of tautomeric structures are possible for pyrazolinones, the usual assignment of ring structures is as shown in (I), (II) and (III). The Chemical Abstracts names for these are (I) 2-pyrazolin-5-one, (II)... 

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