Ethyl 5-chloro-2-indolecarboxylate

5296-86-6

4792-67-0

General procedure for the synthesis of ethyl 5-chloroindole-2-carboxylate from ethyl 2-[(4-chlorophenyl)hydrazinylidene]propionate: 500 g of polyphosphoric acid was mixed with 250 g of phosphoric acid and heated to 70 °C under stirring. 70 g of raw material 4-chlorophenylhydrazine pyruvic acid phenylhydrazone was added in batches, and the reaction temperature was controlled in the range of 70-90 °C. After 1 hour of reaction, it was confirmed that the feedstock was completely consumed. The reaction temperature was continued to be maintained for 40 minutes to ensure complete reaction. After completion of the reaction, the reaction mixture was poured into 1500 g of ice-water mixture and cooled to room temperature. The precipitate was collected by filtration and dried to give a light yellow solid product. Upon further drying, 58 g of ethyl 5-chloroindole-2-carboxylate was obtained in 90% yield.