The general procedure for the synthesis of 4-bromo-2-methyl-2H-indazole from trimethoxonium tetrafluoroborate and 4-bromo-1H-indazole was as follows: with reference to Example 33, 4-bromo-1H-indazole (2.24 g, 11.4 mmol) was dissolved in ethyl acetate (110 mL) and trimethoxonium tetrafluoroborate (2.19 g, 14.8 mmol) was added. The reaction mixture was stirred at room temperature for 3 hours. After completion of the reaction, the reaction solution was diluted with ethyl acetate, washed sequentially with aqueous sodium bicarbonate and dried over anhydrous sodium sulfate. The solvent was removed by concentration under reduced pressure and the resulting residue was purified by silica gel column chromatography (eluent: ethyl acetate/hexane=10/90→40/60) to afford 4-bromo-2-methyl-2H-indazole (2.29 g, 95% yield). The product was characterized by 1H-NMR (CDCl3): δ 4.23 (3H, s), 7.13 (1H, dd, J=8.5,7.2 Hz), 7.23 (1H, dd, J=7.2,0.8 Hz), 7.60-7.44 (1H, m), 7.91 (1H, m). The mass spectrum (ESI+) showed the molecular ion peak m/z 211 (M+H).
