N-Heterocyclic Carbene-Catalyzed Trifluoromethylation of Aromatic N-Tosylaldimines

Typical experimental procedure: to a mixture of imidazolium chloride 1 (25 mg, 0.0724 mmol) in 4 mL of DMF was added potassium tert-butoxide (7 mg, 0.063 mmol). After dissolution of the imidazolium chloride (~ 20 min), N-tosylbenzaldimine 3 (125 mg, 0.483 mmol) and TMSCF₃ (0.1 mL, 0.676 mmol) were added to the contents. The solution was stirred for at room temperature for 4 h, then quenched with water, and extracted with ethyl acetate (3 × 15 mL). The organic layers were combined and successively washed with water and brine, dried over Na₂SO₄, and the solvents were removed in vacuum. The resulting product was purified by silica gel chromatography (10% EtOAc) to obtain 112 mg (72%) of 4-methyl-N-(2,2,2-trifluoro-1-phenylethyl)benzenesulfonamide (4). ¹H NMR (CDCl₃): δ 2.34 (s, 3 H), 4.90 (q, J = 7.5 Hz, 1 H), 5.11 (b, 1 H), 7.12–7.33 (m, 7 H), 7.59 (d, J = 8.4 Hz, 2 H); ¹⁹F NMR (CDCl₃): δ -74.36 (d, J = 7.6 Hz).