Mechanistic studies and quantification of the electrophilicity of aromatic triflones in σ-complexation and S_NAr reactions

The reactions of anilines (N-nucleophiles) and enamines (C-nucleophiles) with NO₂ and SO₂CF₃ substituted aromatic triflones were investigated spectrophotometrically in acetonitrile at 20 C. We found that the second-order rate constants k₁ related to the C-N and C-C bond forming step of these nucleophilic aromatic substitution reactions (S_NAr) and σ-complexation reactions follow the three-parameter equation log k_{(20 C)} = s_N(N + E), allowing the determination of the electrophilicity E of such aromatic triflones for the first time. The ranking of these neutral electron-deficient compounds on the comprehensive electrophilicity scale defined by Mayr et al. reveals that the most electrophilic triflone, the 1,3,5-tris(trifluoromethanesulfonyl)benzene (TTSB), has an electrophilicity higher than that of the 1,3,5-trinitrobenzene (TNB) the common reference aromatic electrophile in anionic σ-complexation chemistry, by roughly 6 units of E. This finding holds promise for expanding the range of coupling reactions which can be envisioned between this series of electron-deficient neutral aromatics and nucleophiles.