876-72-2

25235-85-2

68-12-2

876-72-2

Trichlorophosphorus (3.55 mL) was added slowly and dropwise to N,N-dimethylformamide (10.63 mL) in stirring at 10-20 °C. Subsequently, a solution of 4-chloroindole (2 g, 13.19 mmol) was added at 20-30 °C. The reaction mixture was stirred at 35-37 °C for 45 min, after which it was poured into a stirred mixture of ice (28 g) and water (21 mL). The pH of the reaction solution was adjusted to 8 by adding a solution of sodium hydroxide (6.86 g) in water (36 mL) at 20-30 °C. The mixture was boiled for 5 min, cooled to room temperature and then extracted with ethyl acetate and washed with brine. The organic phases were combined, dried with anhydrous sodium sulfate and concentrated under reduced pressure to give the crude product. The crude product was purified by silica gel column chromatography with 60% petroleum ether/ethyl acetate as eluent to give 4-chloroindole-3-carboxaldehyde (1.037 g, 44% yield) as an off-white solid. m/z = 180 [M+H]+ by LC-MS.