With trifluoromethylcoppe

This reaction has been carried out in DMAC for the trifluoromethylation of activated aryl chlorides such as 2,4-dinitro-l-chlorobenzene [95-97]. Similar trifluoromethylation can be accomplished with trifluoromethylcopper generated from trifluoromethanesulfonyl chloride and copper powder in DMAC [98] (Scheme 33). 

Recently, a unique double difluoromethylene insertion into the carbon-copper bond of pentafluorophenylcopper has been reported [239]. Pentafluoro-phenylcopper reacted with trifluoromethylcopper in DMF at -30 °C to room temperature to form perfluoro-2-phenylethylcopper (C6F5CF2CF2Cu) in high yield, which readily underwent a variety of functionalization reactions with electrophiles [239] (Scheme 79). 

Kobayashi Y, Yamamoto K, Asai T, Nakano M, Kumadaki I (1980) Studies on oiganic fluorine compounds. Part 35. Trifluoromethylation of pyrimidine- and purine-nucleosides with trifluoromethylcopper complex. J Chem Soc Perkin Trans 1 2755-2761... 

Aryl bromides were also perfluoroethylated under these conditions [205] The key to improved yields was the azeotropic removal of water from the sodium perfluoroalkylcarboxylate [205] Partial success was achieved with sodium hepta-fluorobutyrate [204] Related work with halonaphthalene and anthracenes has been reported [206 207] The main limitation of this sodium perfluoroalkylcarboxylate methodology is the need for 2 to 4 equivalents of the salt to achieve reasonable yields A trifluoromethylcopper solution can be prepared by the reaction of bis(tri-fluoromethyl)mercury with copper powder in /V-methylpyrrolidone (NMP) at 140 °C [208] (equation 138) or by the reaction of N-trifluoromethyl-A-nitro-sotnfluoromethane sulfonamide with activated copper in dipolar aprotic solvents [209] This trifluoromethylcopper solution can be used to trifluoromethylate aro matic [209], benzylic [209], and heterocyclic halides [209]... 

Metathesis of the trifluoromethylcadmium or tnfluoromethylzinc reagent with copper (I) salts gives solutions of trifluoromethylcopper [210] (equation 140). Depending on the stoichiometry and copper salt used, either CF3CU L or (Cp3)2Cu can be produced [211],... 

Oxidation of (CF3)2Cu with Oj, Br2, or I2 gives the stable copper(III) compound, (Cp3)4Cu. The X-ray structure of an analogue of this copper(III) compound has been reported [27/]. In the absence of HMPA, the solution of trifluoromethylcopper slowly decomposes at room temperature to give penta-fluoroethylcopper [270] (equation 141). 

A similar distribution of copper reagents can be obtained via the du ect reaction of copper metal with dibromodifluoromethane or bromochlorodifluoromethane in DMF at 85-95 °C [2J2] The oligomerization can be supressed via the addition of alkali metal fluorides to the reaction mixture [272] When HMPAis added to the trifluoromethylcopper solution, decomposition is slowed, and this solution can be used to trifluoromethylate aromatic iodides [270] (equation 143). 

Dihalodifluoromethanes react readily with acid-washed cadmium or zinc powder in DMF at room temperature to produce stable solutions of trifluoromethyl cadmium and zinc reagent, respectively in high yields [42], which undergo a metathesis reaction with copper (I) salts to give a trifluoromethylcopper solution [92] (Scheme 30). 

Another method of trifluoromethylation was based on the electrochemical reaction (copper anode) of 2-bromothiophene 94 with bromotrifluoromethane in DMF. In comparison to usual methods leading to trifluoromethylcopper, this one offered an advantage because it allowed the use of CFsBr instead of the more expensive CF3I. However, the reaction was not selective and gave a mixture of 2- and 3-isomers 78 and 79. The use of 2-iodothiophene 38 as a starting material was found to be more effective 2-trifluoromethylthiophene 78 was obtained in 60 % yield [57],... 

Trifluoromethylpyridine (259) and 2-pentafluoroethylpyridine (260) were obtained by the reaction of 2-iodopyridine (258) and tri- and pentafluoroethylcoo-per at heating in DMF Trifluoromethylcopper and pentafluoroethylcopper are prepared conveniently via the reaction of the solid complex Zn(CF3)Br2DMF with copper(I) bromide in N,N-dimethylformamide (Scheme 76). The maintenance of trifluoromethyl- and pentafluoroethyl derivatives was determined by F NMR spectroscopy in both the mixtures [157],... 

Nowak 1, Robins MJ (2007) Trifluoromethylation of alkenyl bromides and iodides (including 5-iodouracUs) with (CF3)2Hg and Cu ( trifluoromethylcopper ). J Oig Chem 72 2678-2681... 

---