The preparation of Ethyl 5-Bromoindole-2-carboxylate was as follows: A 25 mL Schlenk reaction tube was used, and 69 mg of p-bromoaniline, 9 mg of palladium acetate, and 80 mg of molecular sieve were added. Then, 93 mg of ethyl 2-oxopropionate, 96 mg of acetic acid, and 2 mL of dimethyl sulfoxide were injected. A 200 mL oxygen bulb was attached, and the mixture was stirred at 70 °C for 18 hours using a chemical book. After the reaction was complete, 15 mL of ethyl acetate was added to dilute the reaction solution. The mixture was filtered, washed twice with 10 mL of brine, and the organic phase was separated. The aqueous phase was extracted once with ethyl acetate. The organic phases were combined, and column chromatography was used to separate the target product, yielding 50 mg of pure ethyl 5-bromoindole-2-carboxylate (47% yield).
