7-Bromo-5H-pyrido[4,3-b]indole

Step 1: Preparation of 3-(4-bromobenzene)-4-nitropyridine

2.02 g (10.0 mmol) 3-bromo-4-nitropyridine, 2.20 g (11.0 mmol) 4-bromophenylboronic acid, 0.46 g (0.4 mmol) tetrakis(triphenylphosphine)palladium, and 1.33 g (25 mmol) NaCO3 were dissolved in 60 mL of dioxane and 10 mL of water. The mixture was refluxed at 110 °C for 12 h, cooled, poured into 80 mL of water, and then extracted three times with 100 mL of ethyl acetate. The mixture was dried over anhydrous magnesium sulfate.

Step 2: Preparation of 7-bromo-5H-pyrido[4,3-B]indole

1.68 g of 3-(4-bromobenzene)-4-nitropyridine was dissolved in 60 mL of triethyl phosphite, heated at 110 °C for 3 h under nitrogen protection, cooled, and the triethyl phosphite was removed under reduced pressure. The resulting solid was separated by column chromatography to obtain 1.05 g of brownish-yellow solid product (yield: 71%).