Isolation and Reactivity of Trifluoromethyl Iodonium Salts

The strategic incorporation of the trifluoromethyl (CF₃) functionality within therapeutic or agrochemical agents is a proven strategy for altering their associated physicochemical properties (e.g., metabolic stability, lipophilicity, and bioavailability). Electrophilic trifluoromethylation has emerged as an important methodology for installing the CF₃ moiety onto an array of molecular architectures, and, in particular, CF₃ λ³-iodanes have garnered significant interest because of their unique reactivity and ease of handling. Trifluoromethylations mediated by these hypervalent iodine reagents often require activation through an exogenous Lewis or Brønsted acid; thus, putative intermediates invoked in these transformations are cationic CF₃ iodoniums. These iodoniums have, thus far, eluded isolation and investigation of their innate reactivity (which has encouraged speculation that such species cannot be accessed). A more complete understanding of the mechanistic relevance of CF₃ iodoniums is paramount for the development of new trifluoromethylative strategies involving λ³-iodanes. Here, we demonstrate that CF₃ iodonium salts are readily prepared from common λ³-iodane precursors and exhibit remarkable persistence under ambient conditions. These reagents are competent electrophiles for a variety of trifluoromethylation reactions, and their reactivity is reminiscent of that observed when CF₃ iodanes are activated using Lewis acids. As such, our results suggest the mechanistic relevance of CF₃ iodonium intermediates in trifluoromethylative processes mediated by λ³-iodanes. The isolation of CF₃ iodonium salts also presents the unique opportunity to employ them more generally as mechanistic probes.