Trifluoromethyl group radical formations

An unexpected [1.4] migration of a trifluoromethyl group was observed when azomethine imines were synthesized from hexafluoroacetone azine and alkoxyalkynes. The rearrangement, which occurs at temperatures as low as 0°C, is probably a radical process and results in the formation of A[-(perfluoro-tert-butyl)pyrazoles (79CC792). The formation of... 

Similarly, electrophilic CHj radicals add faster to ethylene than to tetrafluo-rethylene, in which the inductive effects of the fluorine substituents make the double bond somewhat electron deficient. The reverse selectivity is shown by CH3 radicals, which are nucleophilic in character [24]. This parallels the observations in organic chemistry thatcarbonium ion formation is facilitated by replacement of hydrogens by alkyl groups and hindered by CF3 groups. There is a polarization of a electrons towards the trifluoromethyl group, whereas these electrons can be more effectively released by alkyl substituents. 

The potential importance of the trifluoromethoxy radical to atmospheric chemical process was recognized by Francisco and Williams in 1984 [132]. Later, the potential role was amplified by its proposed formation from the degradation of alternative halocarbons [133]. The major production route of the CF3O radical from alternative halocarbons is from the release of the trifluoromethyl group (CF3). The CF3 radical reacts with molecular oxygen to produce the trifluoroperoxy radical (CF3O2), which oxidizes NO to NOj ... 

Both azide and diazirine groups are popular. In the latter case, the trifluormethyl group has been found to be valuable because it stabilizes the diazirine. Also, a side reaction is formation of the analogous diazo compound, and the trifluoromethyl group minimizes interference from this route. Benzophenone derivatives are also popular. The carbonyl abstracts a hydrogen, and then radical recombination creates the cross-link. 

Further research on the substitution of the thiophene 3-position with phenyl groups containing electron-withdrawing or electron-donating groups (such as methyl, methoxy, fluoro, chloro, bromo, trifluoromethyl, sulfoxy) in the para position have lead to polymers with unique features [57]. The electron-withdraw-ing groups allow the formation of a radical anion and thus stabilize the n-doped state. As a result, such conducting polymers can be reversibly oxidized and reduced and electrochromic devices can be built with identical anode and cathode materials [58]. 

Trifluoromethylation of pyrrole (and indole and imidazole) occurs on irradiation of a mixture of the compound with difluorodiiodomethane, again via a SET mechanism involving fragmentation of the radical anion (Scheme 31). The presence of the CF3 group in the final products, 45 and 46, is a result either of secondary decomposition of the initially formed—but not isolated—difluoroiodomethyl derivatives, or of formation of the CF3 anion or radical in situ [94], Perfluoroalkyla-tion of pyrroles can also be achieved by an SrnI mechanism—by reaction with perfluoroalkyl iodides in the presence of magnesium or zinc [95]. Indole, on the other hand, gives a mixture of the seven possible alkylated derivatives when irradiated in the presence of ethyl chloroacetate [96],... 

Data from kinetic studies on hydrogen-atom abstraction by trifluoromethyl radicals ( nerated by photolysis of hexafluoroacetone) from the esters RpCOaMe (Rf = CFs, C2F5, or n-CaF ) have been presented and discussed. The susceptibilities of the methoxy-groups towards hydrogen abstraction are less by a factor of 2—3 than those found with methyl formate and acetate, which contrasts with the claim (based on a study of the esters FCOaMe and CFa COaMe) that fluorine substitution enhances the ease of abstraction. ... 

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