5-Formylindole (2.00 g, 13.8 mmol) was dissolved in acetonitrile (40 mL), and the solution was added with di-tert-butyldicarbonate (3.31 g, 15.2 mmol) and DMAP (16.8 mg, 0.138 mmol), followed by stirring at room temperature for 2.7 hours. The solution was added with a solution of N-(2-hydroxyethyl)piperazine (6.46 g, 49.6 mmol) in acetonitrile (15 mL), and acetic acid (14.2 mL, 248 mmol), then sodium triacetoxyborohydride (13.1 g, 62.0 mmol) was added thereto little by little, followed by stirring at room temperature for 2.5 hours. The reaction mixture was added with water and sodium carbonate to adjust the pH to 9, and extracted with ethyl acetate. The organic layer was washed with saturated brine and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure. The residue was purified by flash column chromatography (chloroform/methanol=9/1, 4/1) to obtain 5-[4-(2-hydroxyethyl)piperazin-1-ylmethyl]indole (4.73 g, yield 95%).
