Synthesis
GENERAL STEPS: Oxalyl chloride (0.3 mL) was slowly added dropwise to ice-bath cooled N,N-dimethylformamide (DMF, 3 mL) under stirring conditions. The reaction mixture was stirred continuously at 0 °C for 1 hour. Subsequently, a solution of 6-chloroindole (4 mmol) dissolved in DMF (1.5 mL) was added slowly dropwise to the above reaction mixture. The resulting mixture was stirred and reacted at room temperature for 5 hours. Upon completion of the reaction, 2 N sodium hydroxide solution (2 mL) was added and the mixture was heated to 100°C maintained for 10 minutes. The reaction solution was cooled and extracted with ethyl acetate (3 x 50 mL). The organic phases were combined and washed sequentially with water and saturated saline. The organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure to obtain the crude product. The crude product was purified by fast column chromatography with the eluent of ethyl acetate/petroleum ether (3:1, v/v) to give pure 6-chloroindole-3-carbaldehyde.
References
[1] Journal of the American Chemical Society, 2006, vol. 128, # 6, p. 1995 - 2004
[2] European Journal of Medicinal Chemistry, 2013, vol. 65, p. 158 - 167
[3] Patent: WO2015/42053, 2015, A1. Location in patent: Paragraph 00331
[4] Patent: WO2016/144704, 2016, A2. Location in patent: Paragraph 00370
[5] Chemical and Pharmaceutical Bulletin, 2016, vol. 64, # 1, p. 34 - 41
