Example XIX- Synthesis of ethyl 7-bromo-1H-indole-2-carboxylate: 11.0 g of 2-bromophenylhydrazine and 550 mg of p-toluenesulfonic acid monohydrate were dissolved in 200 mL of toluene, 6.74 mL of ethyl pyruvate was added, and the reaction was carried out at reflux, also assembled with an aqueous separator, for 2 hours. Upon completion of the reaction, the mixture was cooled to 40°C and combined with a pre-prepared solution (prepared by dissolving 44.75 g of p-toluenesulfonic acid monohydrate in 300 mL of toluene, also fitted with a water separator and refluxed for 2 hours). The combined mixture was continued to reflux the reaction. At the end of the reaction, it was cooled to room temperature and the solvent was removed by distillation under reduced pressure. The residue was dissolved in ethyl acetate and washed sequentially with water and saturated aqueous sodium bicarbonate. The organic phase was dried with anhydrous magnesium sulfate, followed by the addition of activated carbon, stirring for 15 minutes and filtration through diatomaceous earth. This process was repeated twice to ensure purification. The filtrate was concentrated under reduced pressure and the residue was dissolved in a petroleum ether/dichloromethane (7:3) solvent mixture, 30 g of silica gel was added, stirred for 10 minutes and filtered through diatomaceous earth extraction. The silica gel was washed with petroleum ether/dichloromethane (7:3). Finally, the solvent was removed under reduced pressure to give 7.37 g of product in 47% yield. The product was analyzed by HPLC (Method 1): retention time = 3.82 min. mass spectrum (ESI+): m/z = 268 [M+H]+.
