A ’-3-Pyrazolones

Lead tetraacetatejboron fluoride Oxidative ring opening of A" -3-pyrazolones... 

These latter compounds can also be obtained by direct cyclization in a Hantzsch s reaction of the selenosemicarbazone of a /3-ketoester, that is, a l-selenocarbamoyl-3-alkyl-5-pyrazolone (Scheme 21). 

Hydroxy-6-methyl-2-phenylpyridazin-3(2Fr)-one and 4-hydroxy-5-nitropyridazin-3(2FT)-one rearrange in acidic medium to 3-methyl-l-phenylpyrazole-5-carboxylic acid and 4-nitropyrazole-5-carboxylic acid. 4-Hydroxypyridazin-3(2FT)-ones with a hydroxy group or other group at positions 5 or 6, which is easily replaced in alkaline medium, are transformed into 5-(or 3-)pyrazolones with hot alkali. An interesting example is ring contraction of 5-chloro-4-(methylthio)-l-phenylpyridazin-6(lFT)-one which gives, besides pyrazole derivative (127), 4-hydroxy-5-methylthio-l-phenylpyridazin-6(lFf)-one (128 Scheme 41). 

The reaction of pyrazolone bearing a /3-ketoester moiety with aliphatic dibasic functional reagents in EtOH afforded binary ring heterocycles. Whereas when using an excess of a dibasic reagent, dipyrazolo[3,4-z 3, 4 -/][l,2]di-azepine derivatives were obtained <2001SC1335>. 

Three-component reactions of aromatic aldehydes with a series of cyclic CH-acids, for example, with 230, and 5-amino-3-pyrazolones 228 have a high regioselectivity involving the carbon atom at position 4 and yield compounds like 231 [195] (Scheme 3.64). 

This reaction was extended to other (i-dicarbonyl compounds containing a nitro group [474 176], The mechanism of the reaction of hydrazine with 1,3-dicarbonyl compounds is still largely unclear. Nevertheless, important evidence was obtained to indicate that a dihydroxypyrazolidine intermediate is formed in this reaction [477], If hydroxylamine is used instead of free hydrazine in the reaction with nitromalonaldehyde, the product is 4-nitroisoxazole [471], When a mixture of nitrocyanoacetic ester with one equivalent of hydrazine hydrate and a small amount of water is boiled, 5-amino-4-nitro-3-pyrazolone is formed [478],... 

Nitro-3-pyrazolones (52) have been prepared recently by reaction of ethyl-jS-ethoxy-a-nitroacrylate and -crotonate with hydrazine and its derivatives [Eq. (17)].48... 

Pyrazolone and its derivative are the most common ligands used for Tb(III) complexes in electroluminescence. In 1998 the first example of an electroluminescent device using a terbium pyrazolonate complex, tris(l-phenyl-3-methyl-4-isobutyl-5-pyrazolone)-bis-(triphenyl phosphine oxide) terbium [Tb(ip-PMP)3(TPPO)2] (Figure 11.20, compound 36),... 

When 5-bromo-6-methyluracils possessing a phenyl group at the N-l position are treated with alkylamines and hydrazine, ring contraction occurs to hydantoins and 3-pyrazolones, respectively. The latter conversion into the pyrazolone is a double-ring transformation via a hydantoin intermediate. The N-l-phenyl group is essential for of the ring contraction to... 

Two reactions of the non-aromatic 4,4-disubstituted pyrazolones are worthy of mention. Carpino discovered that 4,4-dihalogenopyrazolones (365) and 4-substituted 4-halogenopyrazolones (366) when treated with bases yield a,/3-alkynic and -alkenic acids, respectively (66JOC2867). The reaction proceeds through an oxopyrazolenine (2,3-diazacyc-lopentadienone (367) (B-74MI40408). A modification of the experimental procedure transforms (365) into bimanes (368) (82JOC214), which are formed from (367 R = X). 

As a rule, the presence of a high dielectric constant medium leads to the rise of the dipole moment of the compound. However, the relative increase of the dipole moment varies substantially from one structure to another. For instance, the calculated dipole moment of 2(H)-3-pyrazolone (7) increases by 72% when transferred from the medium with e = 1 to the medium with s = 80, whereas the corresponding change in the dipole moment of pyrazole (3) is only 15%. Therefore, it is questionable to assume constant dipole moment values for a series of congeneric compounds in different dielectric media and derive correlations of the chemical reactivity or physical properties of such series of compounds with some fixed function of the dielectric constant of the solvent (a common approach in the linear free energy relationship studies of solvent effects, cf. [65-67]). 

A uridine phosphate (5), obtained by treatment of uridine 5 -(a-D-glucopyranosyl pyrophosphate) with ammonia, imdergoes hydrazinolysis to D-ribose 5-phosphate (2) and 3-pyrazolone, which establishes the structure of (S) as uridine 5 -phosphate. - (Hydrazinolysis of uridine to pyrazolone, with the liberation of the sugar moiety, had been described, and has served as a useful tool in the determination of the position of attachment of the sugar moiety to the aglycon. ) The 5 -phosphates of adenosine, guanosine, cytidine, and uridine were obtained by enzymic hydrolysis of ribonucleic acid with phosphodiesterases from snake venom and from other sources (such as Streptomyces aureu ). 

In what may foreshadow a versatile and general route to heavily functionalized 1,2-diazocines, as well as to many other larger-ring heterocyclic compounds, oxidative cleavage by periodate of the carbon-carbon double bond of a bicyclic pyrazolone was reported to yield 1,2,6,7-tetrahydro-l-methyl-2-phenyl-l,2-diazocin-3,4,8(5. -trione (29) (85%) (Equation (4)) cleavage of larger-ring... 

In the presence of a catalytic amount of Sc(OTf)3, benzoylhy-drazones react with ketene silyl acetals to afford the corresponding adducts, 8-lV-benzoylhydrazino esters, in high yield (eq 10). Several benzoylhydrazones including those derived from aromatic, aliphatic, a,/3-unsaturated aldehydes, and glyoxylate work well. The reactions of polymer-supported hydrazones with silyl enolates are also catalyzed by Sc(OTf)3 to produce pyrazolone derivatives after base treatment. ... 

Structural overlay of flurtamone, fluridone and NTN-28621 led to a new pyrazolone 28 and pyridine 29, many pyrimidines 30 and some 1,2,4-triazines 31 with the joint possession of 1,3-connected phenyl groups ( 1,3-diaryl-heterocycle ) (Fig. 4.1.11) [34]. A pyrimidine 30 with = CH3O, = H, X = 3-CF3 and... 

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