[Synthesis]
Method 1: Procedure for the synthesis of spiro[indolin-3,4'-piperidin]-2-one. Hydroxyindole (3.00 g, 22.5 mmol) was dissolved in tetrahydrofuran (20 mL) under argon protection, and a tetrahydrofuran solution (20 mL) with benzylbis(2-chloroethyl)amine (5.20 g, 22.5 mmol) was added sequentially to tetrahydrofuran (100 mL). Sodium hydride (1.60 g, 67.6 mmol) was added at room temperature and the mixture was stirred at the same temperature for 1 hour, then warmed up to 90 °C and continued stirring for 3 hours. After the reaction solution was cooled to room temperature, a tetrahydrofuran solution (10 mL) of sodium hydride (0.540 g, 22.5 mmol) was added and stirring was continued at 90 °C for 12 hours. After the reaction was completed, saturated aqueous ammonium chloride solution was added and stirred for 10 min at room temperature. The mixture was poured into a mixture of saturated aqueous sodium bicarbonate solution and brine and extracted with ethyl acetate. The organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: chloroform:methanol=20:1) to afford 1'-benzylspiro[indoline-3,4'-piperidin]-2-one (2.94 g, 44.6% yield) as a yellow amorphous solid.1H-NMR (400 MHz, CDCl3) δ: 1.78-1.93 (m, 2H), 1.95-2.06 (m, 2H), 2.65-2.06 (m, 2H). 2H), 2.65-2.77 (m, 2H), 2.87-3.00 (m, 2H), 3.69 (s, 2H), 6.90 (d, J=7.6Hz, 1H), 7.02 (t, J=7.6Hz, 1H), 7.20 (t, J=7.6Hz, 1H), 7.26 (t, J=6.2Hz, 1H), 7.34 (t, J=6.2Hz, 1H), 7.34 (t, J=7.6Hz, 1H). J=7.6 Hz, 2H), 7.40-7.41 (m, 3H), 8.72 (s, 1H). 1'-Benzylspiro[indoline-3,4'-piperidin]-2-one (300 mg, 1.03 mmol) was dissolved in methanol (5 mL) and 10% palladium carbon (30.0 mg) was added. The mixture was stirred at room temperature under hydrogen atmosphere for 15 hours. The reaction solution was filtered through diatomaceous earth and concentrated under reduced pressure to give spiro[indoline-3,4'-piperidin]-2-one (187 mg, 90.2% yield) as a colorless amorphous solid.1H-NMR (400 MHz, CDCl3) δ: 1.73-1.78 (m, 2H), 1.88-1.94 (m, 2H), 3.06-3.12 (m, 2H) , 3.35-3.41 (m, 2H), 6.92 (d, J=7.7Hz, 1H), 7.04 (t, J=7.7Hz, 1H), 7.22 (t, J=7.7Hz, 1H), 7.42 (d, J=7.7Hz, 1H), 8.70 (br, 1H). |