Water → Indoline-4-ol

Participants

Reaction Steps

A solution of 4-hydroxyindole (6.66 g, 50 mmol) in acetic acid (250 mL) was treated with NaBH3CN (9.42 g, 150 mmol) over 0.5 h, keeping the temperature at <15 C. The mixture was then stirred at room temperature for 1 h and water (5 mL) was added and the solvent evaporated. The residue was dissolved in EtOAc (150 mL) and washed with saturated aq. NaHCO3 and brine, dried and evaporated to give 4-hydroxyindoline as pale crystals (6.76 g. 100%); 1H NMR (δ, CDCl3 DMSO-d6): 6.82 (1H, t, J=8 Hz), 6.20 (1H, d, J=8 Hz), 6.16 (1H, d, J=8 Hz), 3.52 (2H, t, J=8 Hz) and 2.90 (2H, d, J=8 Hz). The crude indoline was dissolved in a mixture of acetic acid (50 mL) and acetic anhydride (50 mL) and heated under reflux for 1 h. The solution was diluted with water (10 mL) and the solvents evaporated. The residue was dissolved in EtOAc (150 mL) and washed with saturated aq. NaHCO3 and brine, dried and evaporated to give 4-acetoxy-1-acetylindoline as pale crystals (9.01 g, 82%), NMR (δ, 90 MHz): 8.07 (1H, d, J=8 Hz), 7.19 (1H, t, J=8 Hz), 6.72 (1H, d, J=8 Hz), 4.05 (2H, t, J=8 Hz), 3.03 (2H, t, J=8 Hz) 2.28 (3H, s) and 2.19 (3H, s).

Provenance & Evidence