In a similar manner to Step 2 of Example 6, 4-chloro-7-[1-(tert-butoxycarbonyl)-5-formylindol-2-yl]isoindolinone (41.0 mg, 0.0998 mmol) was dissolved in acetonitrile (2 mL), and the solution was treated with 4-methylpiperidine (0.048 mL, 0.41 mmol), acetic acid (0.345 mL, 6.03 mmol) and sodium triacetoxyborohydride (169 mg, 0.797 mmol). The reaction mixture was added with water and sodium hydrogen carbonate to adjust the pH of to 9. The mixture was 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 to obtain 4-chloro-7-[1-(tert-butoxycarbonyl)-5-(4-methylpiperidinomethyl)indol-2-yl]isoindolinone (25.0 mg, yield 51%).
