Step 3: Synthesis of tert-butyl 4-bromo-1H-indazole-5-carboxylate
[0245] Tert-butyl 2-bromo-4-fluoro-3-formylbenzoate (4.25 g, 14 mmol) was dissolved in DME (25 mL), hydrazine hydrate (15 mL) was added, and the reaction was heated for 1 hr at 90 °C. After completion of the reaction, it was cooled to room temperature and the reaction mixture was partitioned between ethyl acetate and water. The aqueous layer was extracted with ethyl acetate, the organic phases were combined, dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to give tert-butyl 4-bromo-1H-indazole-5-carboxylate as a brown solid (4.1 g, 100% yield).
LCMS (Method B): retention time (Rx) = 3.63 min, [M + CH3CN + H]+ = 338/340, [M-H] = 295/297.
