4-Methyl pyrazole

BenzoyI-2-(2-chIorophenyl)-2,4-dihydro-5-methyl-3//-pyrazol-3-one, B-OOl26 4-Benzoyl-2-(4-chlorophenyl)-2,4-dihydro-5-methyl-3//-pyrazol-3-one, B-OOl27 Benzoyl cyanide, in 0-00055... 

Amino-4-methylthiazole, A-00257 l,2-Dihydro-5-methyl-3//-pyrazole-3-thione,... 

Glycinethymol blue, G-000I9 2-Guanidino-1,2-dihydro-5-methyl-3//-pyrazol-3-one, G-00045... 

Methylvinyldiazirine (199) rearranges at room temperature in the course of some days. Formation of the linear isomer is followed by electrocyclic ring closure to give 3-methyl-pyrazole. The linear diazo compound could be trapped by its reaction with acids to form esters, while the starting diazirine (199) is inert towards acids (B-71MI50801). 

JA4105) (Section V,A) (2) that of 1,2,3-triazole and 3(5)-methylpyr-azole and the reason why they are liquid at room temperature (89JCC426) (Section V,D,2) and (3) the tautomerism of C-methyl-pyrazoles and -imidazoles (90JA1303) (Section which have already all been dis-... 

However, addition of bromine is accompanied by bromination of 3,5-dimethyl-pyrazolate and pyrazolate ligands at position 4, which is blocked in 4-methyl-pyrazolate. The product of electrochemical oxidation of 175 (R -- R = Me, R = Br) is 177 (R = R = Me, R = Br, X = CIO4). Chlorination proceeds similarly to bromination. 

The reaction of diacetylene and its asymmetric homologs (penta-l,3-diyne, hexa-1,3-diyne) with semicarbazide (72ZOR2605) affords the amides of 3-methyl-pyrazole- 1-carboxylic acid (27) (80°C, EtONa, EtOH, 40 h). Amide 26 undergoes irreversible rearrangement to amide 27 at 80°C (EtONa, EtOH). 

Unsubstituted hydrazine reacts with 4-dialkylaminobut-3-yn-2-ones in dry THF and methylene chloride (50°C, 3 h) to form 3(5)-dialkylamino-5(3)-methyl-pyrazoles (364) in 56-63% yield (87ZOR1635). 

Ethyl 2-chloro-5-(4-chloro-5-difluoromethoxy-1-methyl-pyrazol-3-yl)-4-fluorophenoxyacetate... 

Ring-opening silylformylation has been observed by Murai and coworkers in reactions of cyclic ethers. When the cobalt complex Co2(CO)8 is used as the catalyst in reactions of epoxides, an excess of substrate is required to prevent further reaction of the product siloxy aldehyde.1192 Further investigation led to the discovery of [RhCl(CO)2]2/l-methyl-pyrazole as an effective catalyst combination for the reaction of oxi-ranes119b and oxetanes.J19c For example, oxetane undergoes silylformylation to give 4-(dimethylphenylsiloxy)butanal in 81% yield [Eq. (45)]. 

The isomeric 2-benzyl-3-methyl-pyrazole 1-oxide 193 reacts similarly to give the 3-iodomethyl-pyrazole 196. In this case, the 3-trimethylsilyloxy-methyl compound 197 is formed as a by-product. Most likely, the sily-loxymethyl compound 197 arises when the liberated silyloxyanion acts as a nucleophile replacing the silyloxy group in a regenerative fashion. The silyloxy compound 197 is readily hydrolyzed to hydroxymethyl-pyrazole 198. The 3-methyl-pyrazole 1-oxide 193 reacts five times faster than the 5-methyl isomer 189 as shown by a competition experiment (1992JCS(P1)2555). The iodomethyl-pyrazoles 192 and 196 are versatile starting materials for further transformations in the pyrazole side chain (Scheme 55). 

The lateral protons of the isomeric 4-methyl-pyrazole 1-oxide 199 are not activated, since lateral deprotonation does not give rise to a neutral species. Under similar conditions the 4-methyl isomer 199 reacts at the 3-position producing l-benzyl-3-iodo-4-methyl-pyrazole 202 and... 

These syntheses were carried out in methanol medium at azole concentration from 0.002 to 0.4mol/L the yields were 12-75% (on azoles) and 15-95% (on current) [567,568]. Further, the electrosynthesis was used to produce complexes of methyl-pyrazoles 788 with yields (on ligands) 18-100%, depending on the solvent and metal nature [551,569]. The highest yield was observed in alcohols (especially in methanol Cd, 75% Fe, 84% Ni, 96.7% Co, 99% Zn, 100%), the lowest one in acetonitrile (Zn, 18% Co, 20% Cd, 30% Ni, 74%). The chelates with five-member metal-cycles 789 and 790 [567,568] were isolated in analogous conditions such compounds cannot be obtained from ligands and metal salts ... 

As with substituted imidazoles, substituted pyrazoles may exist as a mixture of tautomers. 5-Methyl pyrazole 4.5 and 3-methyl pyrazole 4.6 exist as a rapidly equilibrating mixture in solution. 

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... 

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