3-trifluoromethyl-5-methylpyrazole

The tautomerism between 3-trifluoromethyl-5-methylpyrazole (44a) and 3-methyl-5-trifluoro-methylpyrazole (44b) has been discussed in detail <83IC774> the authors favor tautomer (44a). In the case of 3(5),4-polymethylenepyrazoles <91JHC647>, the position of the tautomeric equilibrium is directed by the Mills-Nixon effect thus, the 3,4-trimethylene tautomer (65b) is much more stable than the 4,5-one (65a) (AG = 1.3 kcal moU ) <94NJC269> (the x-ray structure of its hydrochloride has been determined <93Mi 30i-02 . The fact that campho[c]pyrazole (221) (see Section 3.01.10.1.2(ii)) exists in the solid state and in solution as the 2//-tautomer is another consequence of the Mills-Nixon effect <93AX(C)724>. 

Fig. 8 The HF-X PANSY-HSQC spectra of 2-bromophenyl-3-trifluoromethyl-5-methylpyrazole recorded on a Varian 600 MHz NMR system equipped with four receivers...

Amino-5-trifluoromethyl-177-pyrazoles were synthesized by cyclocondensation reactions of 4-amino-4-ethoxy-1,1,1-trifluorobut-3-en-2-ones with hydrazines <2006S1485>. / -Alkoxyvinyl trifluoromethyl ketones 555 reacted with methylhydrazine to yield 3-(trifluoromethyl)-l-methylpyrazoles 556 (Equation 113) <2003JHC1087>. 

DMF dmso DMSO dpae dpam dppb dppe dppm dppp ET Hdbpz Hdcmpz Hdfmpz Hdmepz Hdmpz Hdppz Hmpz Hpz Hpz Htmpz IR nbd NMR phen /V./V-Dimethylformamide Dimethyl sulfoxide (ligand) Dimethyl sulfoxide (solvent) 1.2- Bis(diphenylarsino)ethane Bis(diphenylarsino)methane 1.4- Bis(diphenylphosphino)butane 1.2- Bis(diphenylphosphino)ethane Bis(diphenylphosphino)methane 1.3- Bis(diphenylphosphino)propane Electron transfer 3.5- Di-ferf-butylpyrazole 3.5- Dicarbomethoxypyrazole 3.5- Bis(trifluoromethyl)pyrazole 3(5),4-Dimethyl-5(3)-ethylpyrazole 3.5- Dimethylpyrazole 3.5- Diphenylpyrazole 3(5)-Methylpyrazole Pyrazole A general pyrazole 3.4.5- Trimethylpyrazole Infrared spectroscopy Norbomadiene (bicyclo-[2.2.1. ]-heptadiene) Nuclear magnetic resonance 1,10-Phenanthroline... 

The results concerning (40) and (41) show the low sensitivity of the trifluoromethyl group to solvent effects. However, in the case of 3(5)-trifluoromethyl-5(3)-methylpyrazole (44), very different chemical shifts have been observed in the same group of solvents <83IC774> —41.2 in CDCI3, —61.6 in [ HJacetone, and —51.9 in pHJDMSO. This may be due to a modification in the tautomeric equilibrium constant (44a)/(44b) (see Section 3.01.4.4.1). 

A theoretical and experimental study of the FVP of trifluoromethyl-pyrazoles has been published <93JFC(63)27i> the reaction affords fluorinated alkenes and alkynes. Flash vacmun pyrolysis of 1-(alkyn-2 -oyl)-3-methylpyrazoles forms pyrazolo[l,5-a]pyridin-5-ols <94AJC99i>. 

Several trifluoromethylpyrazoles, for instance 3(5)-trifluoromethyl-5(3)-methylpyrazole (44) were used to prepare platinum complexes and the x-ray structure of the resulting complex reported <83 C774>. The ligand tris[3-trifluoromethyl-5-methyl(pyrazol-l-yl)]borate (82) yields a hydridovinyl iridium complex more stable than its j/ -ethylene isomer <89JA5480>. The x-ray structure of the related platinum complex (83) has been described <831C774>. 

Further examples have accumulated. The reactions of oxazoles (257), selenophene (258), and N-methylpyrazole (261) with tetrazine (48) form (256) and (260), (259), and (262) respectively, partly after oxidation (Scheme 47) <88CZ17>. The reactions of 3,6-bis(trifluoromethyl)tetrazine with imidazoles, oxazoles, pyrazoles <89AP(322)415>, indole, and benzo[Z>]thiophene <87CZ8l,87JOC4610> have also been studied. 

A subsequent report describes similar reactions with unmasked trifluoromethyl-1,3-diketones. Following dehydration of the intermediate product, the 5-trifluoro-methylpyrazole was produced regioselectively (Fig. 3.81). ... 

X-Ray crystallography has shown that the 2 1 addition product of diazomethane with 3-aza-l,l,l-trifluoro-2-trifluoromethylhexa-2,4-tra/w-diene is 5,5-bis(trifluoromethyl)-l -(4-methylpyrazol-l -in-3-yl)-l, 2,3-A -triazoline (97) 106... 

The preparation of a range of 3-difluoromethyl-l-methylpyrazole-4-carboxamides and 5-fluoro-l,3-dimethyl-4-carboxamides and carboxanilides are described in some patents. These compounds display important activities as fungicides (Fig. 8a) and bactericides (Fig. 8b) [99], Finally, the 3-trifluoromethylthyopyrazole motif is present in some pesticide hydrazide derivatives [100], and oxazolidines bearing a 3-trifluoromethyl-l-methyl-5-(2,2,2-trifluoro)ethoxypyrazole substituent show activity as herbicides [101]. 

Pyrazolo[l,5-fl]pyrimidine 58 and its hydrated form were obtained by reaction of 5-amino-3-methylpyrazole with 2,6-bis(trifluoromethyl)-4-pyrone (57) [26]... 

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