Acetic Acid → 5-Methoxy-1-benzylindoline

Participants

Reaction Steps

To a solution of 5-methoxyindole (147 mg, 1.00 mmol) in 2.5 mL of tetrahydrofuran was added acetic acid (2.5 mL) and sodium cyanoborohydride (220 mg, 3.50 mmol) at room temperature. After the reaction mixture was stirred at the same temperature for 20 min, benzaldehyde (0.20 mL, 2.0 mmol) was added with additional stirring for 1 h. After the reaction mixture was diluted with water (20 mL) and a 1:1 solution (20 mL) of hexane and ethyl acetate, the aqueous layer was extracted with a 1:1 solution (20 mL) of hexane and ethyl acetate. The combined extracts were washed with saturated NaHCO3 aqueous solution, brine, and dried over MgSO4. After filtration, the filtrate was concentrated in vacuo, and the residue was purified by silica gel column chromatography (hexane/ethyl acetate=90/10 to 80/20) to obtain 5-methoxy-1-benzylindoline (158 mg, 66%) as a sticky oil. To 5-methoxy-1-benzylindoline (4.30 g, 18.0 mmol) was added a solution of 50% hydrogen bromide-acetic acid solution (90 mL) at room temperature. After the reaction mixture was stirred at 115° C. for 22 h, the reaction mixture was neutralized by saturated NaHCO3 aqueous solution (200 mL) and the solution was extracted with ethyl acetate (200 mL) twice. The combined extracts were washed with brine, and dried over MgSO4. After filtration, the filtrate was concentrated in vacuo, and the residue was purified by silica gel column chromatography (hexane/ethyl acetate=80/20 to 70/30) to obtain the title compound (3.78 g, 93%) as a sticky oil.

Provenance & Evidence