Pyrazole 3- bromo-4-phenyl

Pyrazolo[l,2-a]pyrazoles give 3-bromo products unless the 3-position is blocked by a methyl when bromomethyl products arise (80JA4983 81JOC1666, 87JOCI673). When all of the pyrazole ring positions are filled by phenyl groups, chlorination and bromination occur in thepara-positions (74BCJ946) (see also B, 1,2). 

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>. 

Different results were reported for the reactions of benzoylacetonitrile with TV-heteroarylhydrazonoy] halides. Thus, while the reaction of benzoylacetonitrile with AL(3-phenyl-4-bromo-5-pyrazolyl)-C-acetyIformohy-drazonoyl chloride 5d yielded the pyrazole derivative 238 (80JHC209), it was claimed that its reactions with C-acetyl- and C-ethoxycarbonyl-AM3-phenyl-5-pyrazolyl)methanehydrazonoyl chlorides 5a and f under similar reaction conditions afforded the pyrazole derivatives 239a and b (77HCA2171). Hydrazinolysis of 239b afforded the pyrazolopyridazine 240 (77HCA2171). 

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... 

Bromo-N-[4-chloro-2-methyl-6-[(methylamino)Carbonyl]Phenyl]-l-(3-chloro-2-pyridinyl)-1H- pyrazole-5-carboxamide... 

Intramolecular palladium-catalyzed cyclization reactions have also been used to synthesize pyrazole derivatives. iV-Aryl-iV-(o-bromobenzyl)hydrazines 494 participated in a palladium-catalyzed intramolecular amination reaction to give 2-aryl-2//-indazoles 495 (Equation 101) <20000L519>. Palladium-catalyzed intramolecular C-N bond formation of iV-acetamino-2-(2-bromo)arylindolines 496, followed by hydrolysis and air oxidation in the presence of aluminium oxide, allowed the preparation of indolo[l,2-3]indazoles 498 via intermediate 497 (Scheme 58) <2002TL3577>. 3-Substituted pyrazoles have been prepared from the intramolecular cyclization of A -tosyl-iV-(l-aryl/ vinyl-1-propyn-3-yl)hydrazine and then exposme of the reaction mixture of the cyclization to potassium /i //-butoxide <1997SL959>. iV-Aryl-iV -(o-bromobenzyl)hydrazines 499 or [A -aryl-A -(t>-bromobenzyl)hydrazinato-A ]-triphenyl-phosphonium bromides 501 participated in a palladium-catalyzed intramolecular amination reaction to give 1-phenyl-l//-indazoles 500 (Scheme 59) <2001TL2937>. 

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. 

In a study of the tautomerism of 3-(5)-phenylpyrazoles, the X-ray structure of 4-bromo-3-phenylpyrazole showed that a trimeric structure bonded through an H-bond was formed with a considerable twist of the phenyl group about the pyrazole-phenyl bond (92JCS(P2)1737). 

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