78137-76-5

5344-78-5

78137-76-5

Step 1. Synthesis of 4-bromo-3-nitrophenol (C3). 1-Bromo-4-methoxy-2-nitrobenzene (170 g, 0.73 mol) was dissolved in dichloromethane (1.5 L) under argon protection in a 5 L three-necked round-bottomed flask equipped with a thermometer, a pressure equalizing dropping funnel, and an exhaust gas scrubber (1 M aqueous sodium hydroxide solution). The reaction system was cooled to -78 °C. Another boron tribromide (176 mL, 1.86 mol) was dissolved in pre-cooled dichloromethane (1.6 L, 0 °C) and slowly added to the reaction system through the dropping funnel over a period of 2 h. The temperature was raised to -55 °C during the reaction. After addition, the cooling bath was removed and the reaction system was allowed to warm slowly to room temperature with continuous stirring for 48 hours. Subsequently, the reaction mixture was slowly added to cold water (2.0 L, ice/water bath) through a dropping funnel over a period of 4 h. The internal temperature was controlled to be lower than 20 °C, while the generated HBr gas was absorbed using a scrubber (1 M aqueous sodium hydroxide solution). After quenching, the mixture was continued to be stirred for 1 h at room temperature, partitioned and the aqueous layer was extracted with EtOAc (2.0 L). The organic layers (dichloromethane and EtOAc) were combined, washed sequentially with saturated aqueous sodium bicarbonate (2 x 1.2 L; organic layer as lower phase) and brine (1 L; aqueous layer as lower phase), dried over magnesium sulfate and concentrated under reduced pressure. The residue was suspended in dichloromethane (320 mL), slurried overnight, and the solid was collected by filtration. The solid was dissolved in aqueous sodium hydroxide (2.0 M, 500 mL) and extracted with dichloromethane (500 mL). The dichloromethane layer was then extracted with aqueous sodium hydroxide (250 mL), and the combined aqueous layers were acidified with aqueous HCl (1.0 M, 790 mL) to pH 2. The precipitate precipitated was filtered and dried under vacuum at 40 °C for 18 h to afford the target product C3 (125.5 g, 0.5757 mol, 79% yield).1H NMR (400 MHz, CD3OD) δ 6.95 (dd, J = 8.8, 2.9 Hz, 1H), 7.24 (d, J = 2.9 Hz, 1H), 7.57 (d, J = 8.8 Hz, 1H).