General procedure for the synthesis of 4-methyl-1H-indazole from 2,3-dimethylaniline:
Step A: Synthesis of 4-methyl-1H-indazole
Tert-butyl nitrite (30 mL, 248 mmol) was slowly added to a solution of commercially available 2,3-dimethylaniline (20 mL, 165 mmol) in chloroform (600 mL) at room temperature and under nitrogen protection and the reaction mixture was stirred for 15 min. Subsequently, 18-crown-6 (4.3 g, 16.5 mmol) and potassium acetate (32 g, 333 mmol) were added and stirring was continued for 45 minutes. The reaction mixture was heated to reflux for 1 hour, then tert-butyl nitrite (10 mL, 82 mmol) was added and heating and refluxing was continued for 1 hour. After completion of the reaction, the mixture was cooled, the solid precipitate was removed by filtration, and the solids were washed with chloroform (3 x 200 mL). The filtrates were combined, washed with deionized water (400 mL) and dried over anhydrous magnesium sulfate. The solvent was removed by distillation under reduced pressure and the residue was purified by fast column chromatography on silica gel with the eluent of petroleum ether/ethyl acetate (9:1, v/v) to afford 4-methyl-1H-indazole as an off-white solid (5.4 g, 25% yield).
Product characterization data: 1H NMR (CDCl3) δ 2.7 (s, 3H), 6.90 (d, 1H), 7.50 (m, 2H), 8.10 (s, 1H).
