Synthesis
Methyl 1H-indole-5-carboxylate (11 g, 62.3 mmol) was dissolved in 100 mL of N,N-dimethylformamide (DMF) at 0 °C and phosphorus oxychloride (POCl3, 7.9 mL, 84.8 mmol) was added slowly. The reaction mixture was stirred at room temperature for 2 hours. Upon completion of the reaction, the reaction was quenched by the addition of 350 mL of water and the mixture was heated to reflux for 15 minutes to form a brown suspension. After cooling to room temperature, a large amount of precipitate was observed to be generated. Subsequently, an additional 300 mL of water was added and stirring was continued for 10 minutes. The solid product was collected by filtration, washed sequentially with water and hexane, and finally dried under vacuum at 60 °C overnight to afford methyl 3-formylindole-5-carboxylate (12.7 g, 99.5% yield) as a pale pink solid.
References
[1] Patent: US2006/276496, 2006, A1. Location in patent: Page/Page column 62; 63
[2] Patent: WO2017/136395, 2017, A1. Location in patent: Page/Page column 263
[3] Chemistry - A European Journal, 2016, vol. 22, # 2, p. 716 - 723
[4] Patent: US2012/309757, 2012, A1. Location in patent: Page/Page column 170
[5] Journal of Antibiotics, 2017, vol. 70, # 7, p. 832 - 844
