Pentakis(trifluoromethyl)benzenediazonium Cation: A Useful Building Block for the Syntheis of Trifluoromethyl‐Substituted Derivatives

Pentakis(trifluoromethyl)phenol from Nitrobenzene

“…The reaction was carried out as described for C 6 I 5 Cl in ref. 16. Instead of C 6 I 5 Cl, C 6 I 5 NO 2 (may contain C 6 I 4 HNO 2 derivatives) was used: Dispersion of CuBr (9.71 g, 0.050 mol) and DMF (50 mL) was cooled to 0 C, triuoromethyltrimethylsilane (9.50 mL, 0.067 mol) was added.…”

“…88-90 C (lit. 88-90 C) 13,16 19 F NMR spectrum of crude reaction mixture (Reaction I, Spectrum S2 ‡) shows that there are 64% 2,3,4,5-(CF 3 ) 4 -C 6 HNO 2 and 36% 2,3,5,6-(CF 3 ) 4 -C 6 HNO 2 (percentages are converted to 100% leaving out 1a). Aer distillation, according to 19 F NMR spectrum, the ratio is changed to 54 and 46%, respectively (Spectrum S3 ‡).…”

“…None of these methods have very high yields and some of them include rather inconvenient and timeconsuming purication procedures. These methods are: 13,16 (1) Triuoromethylation of hexaiodobenzene with pregenerated CuCF 3 . Phenol 1 is obtained as a by-product with an approximate yield of 20%.…”

“…It has been reported that bromo- 18,19 or even chloro-substituted 20,21 aromatics can be triuoromethylated using a CF 3 À source and different catalytically active metals but these methods are known to be un suitable for substituting halides in electron-rich arenes. 19,21 From the reaction of pentakis(triuoromethyl)benzenediazonium salt with dry NaNO 2 , 16 the mixture of pentakis(tri-uoromethyl)nitrobenzene 2 and -nitrosobenzene 3 was obtained. It was very complicated to separate these two compounds because of their very similar volatility and solubility.…”

“…Nitrobenzene 2 can be obtained from pentakis(triuoromethyl)benzenediazonium salt by reacting it with NaNO 2 , although only at very low yield (13%). 16 Several nitration methods (nitric acid in the presence of other acids; AgNO 2 -BF 3 system 23 ) of pentakis(triuoromethyl) benzene 6 were also carried out to achieve respective nitrobenzene 2 but the efforts were unsuccessful most probably because of very high positive charge on the ipso-carbon of compound 6 and possibly due to steric hindrance by CF 3 groups. It might be possible to obtain nitrobenzene 2 from pentakis(triuoromethyl)benzene anion but its deprotonation requires a rather strong base 13 and an anhydrous oxygen free reaction environment, where it might be challenging to include a NO 2 + cation.…”