[Synthesis]
(a) Synthesis of 4-methoxy-7-bromoindole. 2-Bromo-5-methoxyaniline (4.4 g, 21.8 mmol) was slowly added dropwise to a dichloromethane solution of boron trichloride (1.0 M, 24 mL, 24 mmol) cooled in an ice-water bath. The reaction mixture was gradually warmed to room temperature with continuous stirring for 30 minutes. Subsequently, chloroacetonitrile (4.01 mL, 26.2 mmol), aluminum chloride (4.01 g, 24.0 mmol) and 1,2-dichloroethane (28.5 mL) were added sequentially. The reaction system was heated to 70 °C to evaporate the dichloromethane and then warmed to reflux for 24 hours. Upon completion of the reaction, it was cooled to 0-5 °C and 2.5 M HCl (38.4 mL) was slowly added, followed by heating to 80 °C for 1 h until the solid was completely dissolved. The aqueous phase was separated, the organic phase was extracted with dichloromethane, the organic layers were combined, washed with water and saturated saline in turn, dried over anhydrous sodium sulfate, and concentrated under reduced pressure to give a yellow solid crude product, which was used directly in the next reaction. The above crude product was dissolved in a solvent mixture of dioxane (37 mL) and water (4.2 mL), and sodium borohydride (0.91 g, 24.0 mmol) was added in batches. After stirring for 30 minutes at room temperature to confirm complete consumption of the ingredients, the reaction was heated to reflux for 14 hours. The reaction solution was cooled to room temperature, acidified with concentrated HCl and extracted with ethyl acetate. The organic phase was washed with water and saturated saline, dried over anhydrous sodium sulfate and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (eluent: hexane/ethyl acetate) to afford 4-methoxy-7-bromoindole (1.2 g, 24% yield).1H NMR (400 MHz, CDCl3) δ 3.94 (s, 3H), 6.44 (d, J = 8.21 Hz, 1H), 6.73 (m, 1H), 7.17 (t, J = 2.74 Hz, 1H), 7.22-7H). 1H), 7.22-7.26 (m, 1H), 8.32 (br, 1H); MS (ES, m/z): C9H8BrNO: 227.99 (M+ (79Br)+1), 230.0 (M+ (81Br)+1). |