Reaction Steps
A solution of 1′-(piperidin-4-ylmethyl)-5,6-dihydrospiro[benzo[1,2-b:5,4-b']difuran-3,3′-indol]-2′(1′H)-one (0.29 g, 0.77 mmol), acetone (0.10 mL, 1.4 mmol), sodium cyanoborohydride (0.10 g, 1.51 mmol) and acetic acid (6 drops) in methanol (4 mL), sealed in a well-stoppered round-bottomed flask, was stirred at 60° C. for 16 h. The reaction was cooled, diluted with saturated aqueous sodium bicarbonate (30 mL) and extracted with dichloromethane (3×25 mL). The organic solution was dried over sodium sulfate, filtered and concentrated under reduced pressure. Purification by flash column chromatography with dichloromethane/methanol (14:1) afforded 1′-{[1-(1-methylethyl)piperidin-4-yl]methyl}-5,6-dihydrospiro[benzo[1,2-b:5,4-b′]difuran-3,3′-indol]-2′(1′H)-one (0.21 g, 64%) as a colorless foam: 1H NMR (300 MHz, CD3OD) δ 7.33 (ddd, J=7.8, 7.5, 0.9 Hz, 1H), 7.14-7.05 (m, 3H), 6.44 (s, 1H), 6.32 (s, 1H), 4.81 (d, J=9.2 Hz, 1H), 4.65 (d, J=9.2 Hz, 1H), 4.99 (t, J=8.7 Hz, 2H), 3.74 (dd, J=14.0, 7.2 Hz, 1H), 3.65 (dd, J=14.0, 7.1 Hz, 1H), 3.02-2.91 (m, 4H), 2.77 (septet, J=6.6 Hz, 1H), 2.30-2.18 (m, 2H), 2.00-1.84 (m, 1H), 1.81-1.71 (m, 2H), 1.50-1.34 (m, 2H), 1.08 (d, J=6.6 Hz, 6H); 13C NMR (75 MHz, CD3OD) δ180.3, 163.2, 162.9, 144.1, 134.1, 123.0, 124.8, 124.6, 121.6, 121.4, 120.0, 110.5, 93.7, 81.7, 73.5, 59.2, 56.2, 49.5, 49.4, 46.6, 36.0, 30.7 (2C), 29.9, 18.3, 18.3; MS (ES+) m/z 419.2 (M+1).
