Synthesis
Method 1: Acetic anhydride (100 mL, 1.06 mol, 13.0 eq.) and tert-butanol (8.00 mL, 84.2 mmol, 1.00 eq.) were added to a round-bottom flask equipped with a condenser and a dropping funnel. Fluoroboric acid (14 mL, 78 mmol, 0.95 eq.) was added dropwise. During its addition, the temperature was raised to 80°C. After completion of the exothermic reaction, the mixture was cooled to 5C and cold Et 2 O was added, the precipitate was collected, washed with cold Et 2 O and dried. 2,4,6-Trimethylpyranium tetrafluoroborate was obtained as a colorless solid (11.6 g, 55.4 mmol, 71%). 1H NMR (300 MHz, CD3OD, 300 K) δ= 7.87 (s, 2H, CHarom), 2.88 (s, 6H, 2× CH3), 2.72 (s, 3H, CH3). 13 C NMR (75MHz, CDCl 3, 300K) δ= 179.5 (Cq), 134.1 (Cq), 124.3 (CH), 21.1 (CH 3), 20.7 (CH 3). 19F NMR (282MHz, CD3OD, 300K) δ= -154.7. HRMS (ESI) m/z = 123.0804 Calculated values. MS (ESI): C8H11O [M] +, measured value: 123.0762. Spectral data is consistent with previously reported data.
