Synthesis
General procedure for the synthesis of 5-nitrodihydroindole from 1-(5-nitroindolin-1-yl)ethanone: To a stirred solution of 5-nitroN-acetyldihydroindole (5 g, 31 mmol) in ethanol (50 ml) was slowly added 30% HCl aqueous solution (10 ml) at 50 °C. The reaction mixture was heated to reflux and maintained for 2 hours. Upon completion of the reaction, the mixture was cooled to room temperature and the solvent was subsequently removed by evaporation under reduced pressure. The resulting residue was alkalized by adjusting to pH 9 with ammonium hydroxide solution and the solid was collected by filtration and dried to give the target product 5-nitrodihydroindole as a yellow solid (3.8 g, 97.43% yield). Mass spectrometry analysis showed MS = m/z 164 [M + 1].
References
[1] Patent: WO2009/109999, 2009, A1. Location in patent: Page/Page column 80
[2] Chemical Communications, 2017, vol. 53, # 82, p. 11368 - 11371
[3] Journal of Organic Chemistry, 1955, vol. 20, p. 1538,1541
[4] Zhurnal Obshchei Khimii, 1959, vol. 29, p. 2541,2550; engl. Ausg. S. 2504, 2511
[5] Chemical and Pharmaceutical Bulletin, 2000, vol. 48, # 6, p. 817 - 827
