Organofluorine compounds have attracted much attention, mostly on account of their applications in e.g. pharmaceutical, agrochemical, and materials sciences. Among them, trifluoromethylated aryl compounds (Ar–CF3) are one of the most frequently encountered structural motifs in biologically active compounds. In comparison with Cu-mediated trifluoromethylation reactions, the introduction of a longer-chain perfluoroalkyl groups employing the corresponding Cu(I) species remains largely unexplored. The development of practical, cost-effective and reliable methods for the pentafluoroethylation of aromatic compounds is highly desirable. Tetrafluoroethylene (TFE), which is conventionally employed as a monomer for the generation of tetrafluoroethylene-based polymers and co-polymers, should be an ideal starting material for the preparation of fluorinated compounds, considering that it is a cost-effective and environmentally benign feedstock with negligible GWP100 and ODP values. Recently, we have demonstrated that TFE can insert into a variety Cu(I)–X bonds (X = C, O, B, and Si) to furnish the corresponding fluoroalkylcopper(I) species, Cu–CF2CF2–X. We subsequently envisioned that a pentafluoroethylcopper species (Cu–CF2CF3) should be generated from the fluorocupration of TFE, and that the resulting Cu–CF2CF3 should be an ideal precursor for the versatile construction of pentafluoroethylated aromatic compounds. Thus, we have been focusing our attention on investigating if the fluorocupration of TFE affords a Cu–CF2CF3 species. We discovered that the fluorocupration of TFE occurs in the presence of phen as an auxiliary ligand, which resulted in the clear formation of (phen)CuC2F5 (2) (Scheme 1). We also confirmed that the stoichiometric pentafluoroethylation of iodobenzene with 2 proceeded smoothly, and that the resulting (phen)CuI is readily transformed into (phen)CuF in the presence of an excess of CsF at 80 °C. Based on these stoichiometric findings, we developed the first example for a Cu(I)–catalyzed pentafluoroethylation of aryl iodides in the presence of TFE and CsF, in which refraining from stirring the reaction mixture is the key to suppressing the competing oligomerization of TFE (Scheme 2).

Cu(I)-catalyzed pentafluoroethylation of aryl iodides in the presence of tetrafluoroethylene and CsF

2019 Fall National Meeting

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