[Br:1][C:2]1[CH:7]=[CH:6][C:5]([NH:8][NH2:9])=[CH:4][C:3]=1[O:10][CH3:11].CO[CH:14]([CH3:22])[C:15](OC)(OC)OC>C(O)C>[Br:1][C:2]1[CH:7]=[CH:6][C:5]([N:8]2[CH:22]=[CH:14][CH:15]=[N:9]2)=[CH:4][C:3]=1[O:10][CH3:11]To a solution of (4-bromo-3-methoxyphenyl)hydrazine (62 g, 245 mmol) in ethanol (310 mL) was added tetramethoxypropane (40.2 g, 245 mmol) over a few minutes, and the mixture was heated to an internal temperature of 70° C. The mixture was stirred at 70° C. for 1.5 h then slowly cooled to RT. Ethanol was removed in vacuo and the residue was slurried in EtOAc. The residue was neutralized with 1 M aqueous sodium hydroxide (˜700 mL) to cause precipitation. The biphasic mixture was filtered and the filtrate was extracted with EtOAC, dried over sodium sulfate and concentrated to provide 30 g of 1-(4-bromo-3-methoxyphenyl)-1H-pyrazole as a black solid (30 g, MS: 254 [M+H+].).
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