611-09-6

6146-52-7

611-09-6

The general procedure for the synthesis of 5-nitroindigo red from 5-nitroindole was as follows: a solution of anhydrous acetonitrile (4.0 mL) with 5-nitroindole (0.5 mmol), and iodobenzene diacetate (PIDA, 0.25 mmol) was added sequentially by the addition of a stirrer to a flask that had been pre-dried in an oven. To the reaction mixture, 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO, 0.5 mmol) was added under air atmosphere. The reaction mixture was stirred at room temperature until thin layer chromatography (TLC) analysis showed complete conversion of the feedstock. Upon completion of the reaction, the reaction mixture was extracted with ethyl acetate (3 x 10 mL). The organic phases were combined and dried with anhydrous sodium sulfate (Na2SO4) and subsequently concentrated under reduced pressure to give the crude product. Finally, the crude product was purified by silica gel column chromatography.