4//-Pyrazole, 4,4-dimethyl-3,5-diphenyl

Examples of dynamic processes involving two, three, or four identical tautomers (degenerate or autotrope annular tautomerism) have been found in pyrazoles (type 2 of Table VII). Thus, 3,5-diphenyl-4-bromopyr-azole and 3,5-di-ferf-butylpyrazole (dimers), 3,5-dimethyl-pyrazole (trimer). 

Dipolar cycloaddition of 2-diazopropane and 1,3-diphenyldinitrilimine to E- and Z-methoxybutenynes occurs at the triple bond to form 3,3-dimethyl-5-(2-methoxyvinyl)pyrazole (168) and a mixture of , Z-l,3-diphenyl-4- (169) and -5-(2-methoxyvinyl)pyrazole (170) [70CR(C)80]. 

The following procedure represents a convenient preparative method leading to the synthesis of copper(I) pyrazolates, namely, [Cu(pz)]n (Hpz = IH-pyrazole), [Cu(dmpz)]3 (Hdmpz = 3,5-dimethyl-lH-pyrazole), [Cu(dcmpz)] (Hdcmpz = dimethyl- lf/-pyrazole-3,5-dicarboxylate), [Cu(dctpz)]n (Hdctpz = di-ferf-butyl-1 f/-pyrazole-3,5-dicarboxylate), and [Cu(dppz)]4 (Hdppz = 3,5-diphenyl-lH-pyrazole). In all cases, high yields ( >90%) of the pure products are obtained. 

Bromn-4,5-dihydro-5-hydroperoxy-4,4-dimethyl-3,5-diphenyl-3H-pyrazole (1). Mol. wt. 361.25. m.p. 77 80". 

Oxidation of organic substrates. This hydroperoxide converts 2,3-dimethyl-2-butcne into tetramethylethylene oxide with simultaneous formation of 3-bromo-4,5-dihydro-5-hydroxy-4,4-dimethyl-3,5-diphenyl-3H-pyrazole (2). Dialkyl olefins, however, are not epoxidized by I. Enol ethers are converted to a variety of epoxide rearrangement products.2... 

The proton spectra of 1-substituted 3-nitropyrazoles [296], 5-substituted 3-methyl-l-aryl-4-nitropyrazoles [297, 298], 1,3- and l,5-diphenyl-4-nitropyra-zoles [281], 5-iodo-4-nitro-l,3-dimethylpyrazole [299], l-methyl-3-nitro-4- and l,3-methyl-4-nitro-5-phenylethynylpyrazoles [300], l-methyl-3-nitro-5-methoxy-carbonylpyrazole [301], l-methyl-3-nitro- and l-methyl-5-nitro-4-cyanopyrazoles [302], A-(2,4-dinitrophenyl)nitropyrazoles [303], a- and [3-anomers of 3-nitro-and4-nitropyrazolyl-l-ribonucleosides [304, 305], 3-substituted 1,5-dimethyl- [306] and 5-substituted l,3-dimethyl-4-nitropyrazoles [279], l-acetyl-3-anilino-4-nitro-5-dimethylaminopyrazoles [307], 3-substituted 4-nitro-5-carboxylic acid derivatives [308, 309], 4-nitropyrazolo[4,3-e][l, 4]diazepin-5,8-diones showing antimicrobial activity [310], l-heteryl-4-nitropyrazole derivatives [311], 3-nitro- and 5-nitro-l-methylpyrazole [312], 4-nitro-5-(trimethylsilyl)pyrazole [313], 3-methyl-4-nitro-pyrazol-5-ones [298], and some other nitropyrazoles [248, 314-320] have been examined. 

The same carbene can also be generated by thermolysis of 2,2-diphenyl-5-diphenyl-methylene-2,5-dihydro-l,3,4-oxadiazole. When the reaction was carried out in the presence of either dimethyl ( )-but-2-enedioate or dimethyl (Z)-but-2-enedioate one cyclopropane, dimethyl 3,3-diphenylcyclopropane-tranj-l,2-dicarboxylate (1), was formed, most likely via a 4,5-dihydro-3//-pyrazole intermediate. ... 

In so far as 4//-pyrazoles can be regarded as azadienes, the most obvious method of achieving 3,5-addition would seem to be through a Diels-Alder reaction. Unfortunately, these pyrazoles normally only react in this way with the most reactive dienophiles (4-phenyl-l,2,4-triazole-3,5-dione and cyclobutadiene ). It has recently been shown, however, that under acid catalysis a much wider range of dienophiles can be used, greatly extending the range of cyclopropyl derivatives that can be made. A typical example of an uncatalyzed reaction is that between 4,4-dimethyl-3,5-diphenyl-4i/-pyrazole and cyclobutadiene which yielded, after deazetization, 3,3-dimethyl-2,4-diphenyltricyclo[3.2.0.0 - ]hept-6-ene... 

To a cold (0 "C), magnetically stirred solution of 4,4-dimethyl-3,5-diphenyl-3i/-pyrazole (2.4 g, 10 mmol) and cyclobutadieneirontricarbonyl (1.92 g, 10 mmol) in acetone (125 mL) under Nj was added ceric ammonium nitrate (27.4 g, 50 mmol) in portions over 30 min. The resultant slurry was poured into anhyd EtjO and the precipitated cerium salts were removed by filtration. The filtrates from two identical runs were evaporated and the combined crude product chromatographed (silica gel, EtjO/hexane 1 9). Recrystallization (hexane) gave 7,8-diaza-eui7o-9,9-dimethyl-l,6-diphenyltricyclo[4.2.1.0 ]nona-3,7-diene(9) as white crystals yield 4.09 g (68%) mp 153-154 "C (dec.). A solution of the diazene 9 (100 mg, 0.33 mmol) in EtjO (2 mL) was irradiated for 3 h with a 200-W Hanovia lamp (Pyrex filter). The progress of the reaction was monitored by TLC. Removal of the solvent gave 10 yield 90 mg (100%) mp 65-67 C. 

The intermediacy of diazoalkenes in the photochemical conversion of, e.g., 3,3-dimethyl-4,5-diphenyl-3//-pyrazole to 3,3-dimcthyl-l, 2-diphenylcyclopropcne (1) has been established. ... 

In the case of 3-aryl-substituted 3//-pyrazoles [e.g. dimethyl 3,3-diphenyl-3//-pyrazole-4,5-dicarboxylate (7)] indene formation often competes with formation of the cycloprop-... 

G477> this compound crystallizes in a noncentrosymmetric group (a chiral helix) and owing to its high dipole moment shows nonlinear optical properties in the solid state. The structures of other N7/-pyrazoles bearing a 4-nitro substituent were determined and compared with those of the corresponding 4-unsubstituted-pyrazoles (pyrazole itself (7), 3,5-dimethyl (19), 3,5-diphenyl (17),... 

Ozonolyse von 2,5-Diphenyl-l-methyl- und 3,5-Dimethyl-l-phenyl-lH-pyrazol und nachfol-gende Reduktion der Ozonolyse-Produkte mit Natriumboranat fiihrt zu Carbonsaure-ami-den2348 ... 

Bis-[l,3-Benzothiazol-2-ylthio]-organo- 997 Bis-[4-tert.-butyl-1,3-thiazol-2-yl]- 71 Bis-[l,3-dimethyl-lH-pyrazol-5-yl]- 557 Bis-[4,5-diphenyl-l,3-thiazol-2-yl]- 71 Bis-[4-methyl-l,3-thiazol-2-yl]- 71 Bis-[5-nitro-l,3-thiazol-2-yl]- 244 Bis-[l,3-thiazol-2-yl]- 70, 71 Ethyl- 337... 

Diazotization of 4-[(4-aminophenyl)sulfonamido]-2,6-dimethyl pyrimidine 10, followed by coupling of the diazonium salt with ethyl 3-oxobutanoate 11a or l,3-diphenyl-l,3-propanedione lib, afforded hydrazones 12a,b. Reaction of hydrazone 12a with aminoguanidine nitrate in refluxing acetic acid yielded the pyrazol-3-one 13a in 55% yield (00JIC42) (Scheme 4). 

The universal synthetic method used to prepare an Ir(C N)2(LX)-type complex is shown in Fig. 5. Dimer complex [Ir(C N)2Cl]2 is readily prepared from reaction of the ligand precursor and IrCl3-nH20 [79], and chloro-ion ligands can be subsequently replaced with an LX chelate. The most studied ancillary ligand LX is acac, but it can be varied with other monoanionic bidentate ligands, such as picolinic acid, N-methylsalicylimine [23], 2-(5-phenyl-4//-[l,2,4]triazol-3-yl)-pyr-idine [28], 2,2,6,6-tetramethyl-3,5-heptanedionate, 1-phenyl-4,4-dimethyl-1,3-pen-tanedionate, l,3-diphenyl-l,3-propanedionate, pyrazolyl, pyrazolyl-borate [80], and (2-pyridyl) pyrazolate derivatives [81]. 

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