Synthesis
Step 1a. 6-Chloro-1H-indazole (3.0 g, 19.66 mmol) was suspended in 2 M NaOH solution (70 mL) and a solution of bromine (2.32 g, 14.52 mmol) in 2 M NaOH (30 mL) was added slowly and dropwise. The reaction mixture was stirred at room temperature for 1.5 hours. Upon completion of the reaction, the pH was adjusted to 8 with 3 M HCl, followed by liquid-liquid partitioning with ethyl acetate and brine. The organic phase was dried with anhydrous sodium sulfate, filtered and concentrated. The crude product was purified by silica gel column chromatography (eluent: ethyl acetate/petroleum ether) to afford the target compound 3-bromo-6-chloro-1H-indazole as a yellow solid (3.4 g, 44% yield).ESI-MS m/z = 231.00, 233.00 [M + H]+.
References
[1] Synthesis, 2011, # 16, p. 2651 - 2663
[2] Patent: WO2016/183266, 2016, A1. Location in patent: Page/Page column 44-45
[3] Patent: US2016/289212, 2016, A1. Location in patent: Paragraph 0191
[4] Patent: WO2013/169907, 2013, A1. Location in patent: Paragraph 00115
