3-Phenyl-5-methylpyrazole

The reaction of the isomeric 3-iodo-l-methylpyrazole-4-carboxylic acid with copper phenyl- and p-amylacetylide also leads to closure of the pyranopyrazole... 

The acidity of 4-ethynyl- 1-methylpyrazole is lower than that of phenylacetylene (pK =29.1) [75IZV2351 79JCS(P2)726 84IZV923]. The ethynyl group in other positions of pyrazoles has smaller values i.e., 4-pyrazolyl radicals have a weaker electron-acceptor characteristic than the phenyl ring. 

The cyclization of l-alkoxybut-l-en-3-ynes with hydrazine was first achieved by Franke and Kraft (55AG395). By heating 1-methoxybut- l-en-3-yne with hydrazine sulfate in an aqueous alcohol medium they obtained 3(5)-methylpyrazole (13) in high yield. Winter (63HCA1754) used the cyclization of 1-methoxybut-l-en-3-yne with hydrazine hydrate and phenylhydrazine to establish the structure of the initial enyne ether [in this case a mixture of l-phenyl-3(5)-propylpyrazoles was obtained]. The reaction with hydrazine sulfate gives only one product, 3(5)-propyl-pyr azole. 

Likewise, the ynaminoketones with phenylhydrazine give a similar mixture of isomerie l-phenyl-3-dialkylammo-5-methylpyrazoles (369) and l-phenyl-5-dialkylamino-3-methylpyrazoles (370) in the same 3 4 ratio (87ZOR1635). 

The triselenadiborolanes 3,5-R2-l,2,4,3,5-Se3B2 R=Et (33), Pr readily formed coordination adducts with two equivalents of pyridine, 3,5-dime-thylpyridine, and 3-chloropyridine.168 With one equivalent of base, only one of the B atoms became coordinated, and surprisingly, the system was not fluxional at room temperature.168 The addition of two equivalents of pyrazole to 33 (Scheme 7) resulted in a brown suspension and a yellow solution. Crystals of a B2N4Se2-bicyclo[2.2.2]octane were formed upon cooling this solution to —80 °C. With bulkier pyrazole derivatives (phenyl-pyrazole), the B2N4Se-bicyclo[2.2.1] heptanes were formed.169... 

The last group of metal-free azo pigments are the pyrazolone compounds, the most commonly used examples being made from the coupling component l-phenyl-3-methylpyrazol-5-one, also used in making azo dyes. The two most important pigments are... 

For orange colours, simple 2-naphthol derivatives are the most commonly used coupling components as, for instance, in 2,4-dinitroaniline—>2-naphthol (4.118 Cl Pigment Orange 5). As in the yellow series, superior disazo pigments can be prepared using 3,3 -dichlorobenzidine as tetrazo component with derivatives of 1 -phenyl-3-methylpyrazol-5-one as couplers. 

Chloro-4-(2-chlorobenzoyl)-1 -phenyl-3-methylpyrazole yields 1 -phenyl-4-(2-chlorophenyl)-3-methylpyrazole upon treatment with hydrazine (17CB737). Other derivatives of pyrazolo [3,4-c] pyrazoles have been similarly prepared (22CB291). 

While most superoxo complexes—in contrast to peroxo compounds— have been assigned a bent, end-on coordination mode [9], the superoxide ligand of Tp Cr(02)Ph was suggested to exhibit the more unusual side-on (r] ) coordination [10]. The reactivity of the complex did not allow for the determination of its molecular structure however, close analogs could be isolated, crystallized and structurally characterized by X-ray diffraction. For example, the reaction of [Tp Cr(pz H)]BARF (pz H = 3-tert-butyl-5-methylpyrazole, BARF = tetrakis(3,5-bis(trifiuoromethyl)phenyl)borate) with O2 produced the stable dioxygen complex [Tp Cr(pz H)( ] -02)]BARF (Scheme 3, bottom), which featured a side-on bound superoxide ligand (do-o = 1.327(5) A, vo-o = 1072 cm ) [11]. Other structurally characterized... 

The hydrogen atoms of the methyl and carboxyl groups of 1 -phenyl-3-methylpyrazole-5-carboxylic acid are replaced by deuterium under mildly alkaline conditions.538 No other example of hydrogen exchange in a methylpyrazole seems to have been recorded. 

The introduction of other electron-withdrawing or -donating groups enables nitration of one or another of the rings to be accomplished selectively. Thus, l-phenyl-3-methylpyrazole is nitrated only in the pyrazole ring, whereas 1 -phenylpyrazole-3-carboxylic acid nitrates only in the para position of the benzene ring.586 The only dinitro-pyrazole recorded was obtained from 3-nitro-5-(pyrid-3-yl)-pyrazole.249,587 In the nitration product (54) the nitro group at... 

Snyder703 was the first to obtain an organo-lithium derivative of pyrazole, when he treated l-phenyl-3-methylpyrazole with butyl-lithium and then carbon dioxide, and isolated l-phenyl-3-methyl-pyrazole-5-carboxylic acid. Subsequently, Alley704 showed that 1-phenyl- and 1-methyl-pyrazoles are also metallated in the 5-position by the treatment with organo-lithium compounds. Hiittell and Schon705 studied the pyrazolyl lithium derivatives in detail, and showed that in pyrazole itself the 3- and 5-hydrogen atoms were more... 

Diamino-l-phenyl-3-methylpyrazole dihydrochloride (78) reacted with sulfur monochloride in DMF at 0°C to afford 6-methyl-4-phenylpyrazolo[3,4-c][l,2,5]thiadiazole (79) in 36% yield (Scheme 17) <81JOC4065>. 

Methyl-4-phenylpyrazolo[3,4-c][l,2,5]selenadiazole (80) has been obtained from 4,5-diamino-1-phenyl-3-methylpyrazole by two methods (Scheme 17). The pyrazole dihydrochloride (78) on... 

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