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To a solution of 5-methoxy-1H-indazole (1.0 g, 6.7 mmol) in ethyl acetate (10 mL) was added trimethoxonium tetrafluoroborate (1.3 g, 8.9 mmol). The reaction mixture was stirred at room temperature for 3 hours. After the reaction was completed, saturated aqueous sodium bicarbonate solution (10 mL) was added for neutralization and extracted with ethyl acetate (20 mL). The organic phases were combined, dried with anhydrous sodium sulfate and concentrated under reduced pressure. The crude product was purified by silica gel fast column chromatography (petroleum ether/ethyl acetate = 2/1) to afford 5-methoxy-2-methyl-2H-indazole (0.64 g, 59% yield) as a yellow solid. Mass spectrometry analysis: [M + H]+ m/z calculated value (C9H10N2O) was 163, measured value was 163.

[1] Journal of Organic Chemistry, 2003, vol. 68, # 10, p. 4093 - 4095
[2] Patent: WO2016/44138, 2016, A1. Location in patent: Paragraph 00116
[3] Patent: WO2007/3419, 2007, A1. Location in patent: Page/Page column 69-72