16732-57-3

yellow to brown powder

To a dry 500 mL three-necked flask, ethyl 2-[2-(4-nitrophenyl)hydrazinylidene]propionate (10 g, 0.042 mol) was added sequentially. Polyphosphoric acid (110 g) was slowly heated to 100 °C under mechanical stirring. The reaction was maintained at this temperature for 2 h. The progress of the reaction was monitored by thin layer chromatography (TLC). After confirming the completion of the reaction, the heating was stopped. The reaction mixture was cooled to room temperature and the reaction was quenched by slowly pouring it into a large amount of ice water. The precipitate was collected by filtration and the filter cake was washed with cold water. The resulting green solid product, ethyl 5-nitroindole-2-carboxylate, was dried in a vacuum drying oven to give 8.9 g in 90.2% yield.

[1] Patent: CN107739368, 2018, A. Location in patent: Paragraph 0036; 0038; 0040
[2] Synthesis, 1980, # 3, p. 222 - 223
[3] Patent: US9226970, 2016, B2. Location in patent: Page/Page column 39
[4] Journal of the American Chemical Society, 1958, vol. 80, p. 4621
[5] Farmaco, Edizione Scientifica, 1958, vol. 13, p. 105,109