Oxonium, trimethyl-, tetrafluoroborate(1-) (1:1) → 1-Methoxy-4-methyl-2-[4-(trifluoromethyl)phenyl]-2H-1,2,3-triazolium tetrafluoroborate

To a stirred solution of 4-methyl-2-[4-(trifluoromethyl)phenyl]-2H-1,2,3-triazole 1-oxide (i.e. the product of Step A, 5.22 g, 21.5 mmol) in dichloromethane (100 mL) was added trimethyloxonium tetrafluoroborate (4.13 g, 27.9 mmol). The reaction mixture was stirred at 23° C. for 65 h, then concentrated under reduced pressure to afford a crude mixture of the title compound as a brown oil which was used directly in the next step without further purification.