4- Bromo-4- -pyrazol-3-ones

An analogous approach has been utilized to generate the central piperazine ring of 337 via dimerization of 5-amino-4-bromo-2-phenyl-2,4-dihydro-pyrazol-3-one 336 under basic conditions in good yield (Equation 91) <2003HAC211>. 

In the case of 5-bromo-3,4-dimethyl-l-phenyl-l/f, 6//-pyrano[2,3-c]pyrazol-6-one (59), mixed acid nitration results not only in para substitution in the phenyl ring, but also in ipso attack at the 5-position to yield... 

The reaction has proceeded satisfactorily with one or two benzoyl groups present,153,507 but a benzoyl group in position 1 has also been eliminated.153 The oxidation proceeds similarly when position 4 is substituted.608 Pyrazoline itself and monoalkyl- and monoaryl-pyrazolines give the corresponding pyrazoles only in small yield on oxidation with bromine.509,510 In the majority of cases bromination occurs together with oxidation, and often brominated products are the only ones isolated. Thus 1,3,5-triphenylpyrazoline yields a tribromide of unknown constitution.49 The hydro bromide of 4-bromopyrazole (43) was obtained almost quantitatively from 3-butoxy-J1-pyrazoline (42).611A mixture of 1,5-dimethylpyrazole and the 4-bromo compound... 

The tautomerism in the solid state and in solution of five 4-bromo-1 //-pyrazoles has been studied by multinuclear magnetic resonance spectroscopy <07T8104>. When there is a bromine atom at position 3(5), the tautomer present in all cases in the solid state and in the solution state is the 3-bromo one. 

Bromo-l-methylbenzo[c]pyrazolo[l,2-a]pyrazole-3,9-dione 4-(p-Chlorobenzal)-l,3-diphenyl-2-pyrazolin-5-one... 

A similar preference for cis- or emfo-products is generally observed in the reactions of thermally generated chloro(trichloroethenyl)carbene with a large variety of olefins (see Vol. E 19b, p 740)11. The alkynyl-substituted earbene 4 obtained by photolysis of 5-bromoethynyl-3,3-dimethyl-3//-pyrazole adds exo selectively to 3-cyclohexenone to give an 80 20 mixture of 7-bromo-7-(4-methyl-3-penten-l-ynyl)bicyclo[4.1.0]heptan-3-one (5/6)12. The reaction of chlorophenylcarbene and cyclohexene affords 7-chloro-7-phenylbicyclo[4.1.0]heptane with moderate endo preference (see Vol. E19b, p984), i. 

Earlier, Kutterer et al. (05BMCL2527) (Scheme 80) reported that 4-methyl-1,2-fazs(4-chlorophenyl)pyrazolidine-3,5-dione 348 with 2-bromo-l-(2,4-difluoro-phenyl)ethanone 349 in toluene containing DIPEA under MW heating (900 W) for 1 min gave 4 -alkyl-4-methyl-pyrazolidine-3,5-dione 350 and 4-methyl-5-alkyloxy-pyrazol-3-one 351. Although compound 351 was evaluated as new inhibitor of bacterial cell wall biosynthesis, no separation and yields of 350 and 351 were reported. 

From 3-bromo(or chloro)-4-methoxychromen-2-one. Okamoto and co-workers (99JHC767) (Scheme 87) described an efficient method of converting chromen-3-ones 387a,b into 4-bromo(or chloro)-l,2-di-hydro-5-(2-hydroxyphenyl)pyrazol-3-ones 390a,b and 4-hydrazono(or... 

Under these conditions, the expected 1,3,4-thiadiazines 8o, 8p, 8r, and 8s cannot be isolated from the reactions of thiobenzhydrazide or thiophenylacetic acid hydrazide with 2-bromo-l-phenylpropan-l-one and 2-bromo-l-phenylbutan-l-one because partial desulfurization to the pyrazoles occurs. However, the synthesis of these compounds is possible by dehydration of the corresponding 4,5-dihydro-6//-l,3,4-thiadiazin-5-ols. Compounds 8a, h and 8n-s can also be obtained from the respective 4,5-dihydro-6//-l,3,4-thiadiazin-5-ols (Method B). 

Tietze et al. (88LA9) (Scheme 77) alkylated 2-hydroxybenzaldehyde with 5-bromo-2-methylpent-2-ene and 1 //-pyrrole-2-carbaldehyde with l-bromo-3-methyl-but-2-ene and obtained the corresponding aryl aldehydes 246 and 248. Condensation of the latter with pyrazol-3-one 262 in acetonitrile containing ethylenediamine diacetate as a catalyst provided (7 /Z)-4- 2-[(4-methylpent-3-enyl)oxy]benzylidine -pyrazol-3-one 247 and ( /Z)-4- [l-(3-methylbut-2-enyl)-177-pyrrol-2-yl]methylene -pyrazol-3-one 249, in 67 and 99% yield, respectively. 

Hydroxycoumarin is converted in high yield by aryl-iodonium acetates [e.g., PhI(OAc)2] into the betaines (158) which rearrange in hot acetic acid to the 3-iodocoumarin (159) and are converted by hydrochloric or hydrobromic acid into 3-chloro- or 3-bromo-4-hydroxycoumarin.171 On reaction with arylhydrazines, 3-acetyl-4-hydroxycoumarin is converted into pyrazoles (160) which are cyclized to the benzopyrano[2,3-c]pyrazol-4-ones (161).172... 

A consecutive three-component synthesis of pyrazoles [67] starting from (hetero)aroyl chlorides, terminal alkynes, and hydrazines represents an excellent entry to more sophisticated one-pot transformations on the regioselectively substituted heterocyclic core. For instance, the catenation of an electrophilic halogenation step led to a one-pot four-component synthesis of 4-halo pyrazoles 36 (halo = chloro or bromo) in good to excellent yield (Scheme 12.24) [68]. 

Z)-5-Bromo-5 -(2-(5-bromo-l-(4-methoxybenzyl)-2-oxoindolin-3-ylidene) by draziny 1)-1 -(4-methoxybenzyl)-1, 2 -dihydrospiro[indoline-3,3 -pyrazol]-2-one (4d) Dark brown powder mp 163 °C 5deld 63%... 

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