In a similar manner to Step 2 of Example 6, 4-chloro-7-[1-(tert-butoxycarbonyl)-5-formylindol-2-yl]isoindolinone (40.0 mg, 0.0974 mmol) was dissolved in acetonitrile (2 mL), and the solution was treated with N,N-dimethylethylenediamine (0.043 mL, 0.39 mmol), acetic acid (0.112 mL, 1.96 mmol) and sodium triacetoxyborohydride (103 mg, 0.486 mmol). The reaction mixture was added with water and sodium carbonate to adjust the pH to 9, followed by extracting 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-[(2-dimethylaminoethyl)aminomethyl]indol-2-yl)isoindolinone (51.5 mg).
