4770-37-0

2380-86-1

4770-37-0

General procedure for the synthesis of 6-hydroxyindoline from 6-hydroxyindole: Sodium cyanoborohydride (NaBH3CN, 1.4 g, 22.60 mmol) was slowly added to a solution of 6-hydroxyindole (1.0 g, 7.51 mmol) in acetic acid (AcOH, 20 mL) at 0 °C. Subsequently, the reaction mixture was stirred under nitrogen (N2) protection for 3 h at room temperature. Upon completion of the reaction, the reaction was quenched with saturated ammonium chloride (NH4Cl, 3 mL) solution and concentrated under reduced pressure to give a residue. The residue was redissolved in ethyl acetate (EtOAc, 50 mL) and washed sequentially with saturated sodium bicarbonate (NaHCO3, 50 mL) solution and brine (50 mL). The organic phase was dried with anhydrous sodium sulfate (Na2SO4), filtered and concentrated. The residue was purified by fast column chromatography using petroleum ether/ethyl acetate (5:1→3:1→2:1, v/v) as eluent to afford the target product 6-hydroxyindoline (0.61 g, 60% yield) as a brown solid. The structure of the product was confirmed by 1H NMR (400 MHz, DMSO-d6) and 13C NMR (101 MHz, DMSO-d6).