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New methods of free-radical perfluoroalkylation of aromatics and alkenes are reported. n-C₄F₉I has been utilized as source of C₄F₉^• radical through iodine abstraction by phenyl or methyl radical. The reaction with alkenes, carried out in the presence of catalytic amount of Cu(OAc)₂, leads to substitution by a mechanism substantially identical to the aromatic substitution and not to the usual chain addition of perfluoroalkyl group and iodine atom to the double bond. This has allowed to measure for the first time the absolute rate constants and the partial rate factors for the homolytic aromatic perfluoroalkylation by competition kinetics. The C₄F₉^• radical shows a clear-cut electrophilic character in the aromatic substitution, as already reported for the addition to alkenes, but the low regio- and chemoselectivities suggest that the polar effect is not the main factor in determining the high reactivity of perfluoroalkyl radicals …