Reaction Steps
To a stirred solution of tert-butyl 4-[(5,5-dimethyl-2′-oxo-5,6-dihydrospiro[benzo[1,2-b:5,4-b′]difuran-3,3′-indol]-1′(2′H)-yl)methyl]piperidine-1-carboxylate (80 mg, 0.16 m mol) in 10.0 mL dichloromethane was added hydrobromic acid (0.50 mL of hydrobromic acid ≧33% in glacial acetic acid, 1.60 mmol) slowly at 0° C. The mixture was stirred at ambient temperature for one hour and concentrated in vacuo to dryness. The residue was treated with 10.0 mL of 2 N sodium hydroxide solution and extracted with dichloromethane (3×30.0 mL). The combined organic layers was washed with brine (100 mL), dried over anhydrous sodium sulfate and filtered. The filtrate was concentrated in vacuo to dryness. The residue was subjected to column chromatography (2% methanol in ethyl acetate) to give 5,5-dimethyl-1′-(piperidin-4-ylmethyl)-5,6-dihydrospiro[benzo[1,2-b:5,4-b′]difuran-3,3′-indol]-2′(1′H)-one (0.03 g, 46%), which was treated with 2.0 M HCl in diethyl ether to give the title compound: 1H NMR (300 MHz, CD3OD) δ 7.41 (td, 1H), 7.25-7.12 (m, 3H), 6.43 (s, 1H), 6.37 (s, 1H), 4.87 (d, 1H), 4.72 (d, 1H), 4.23 (s, 2H), 3.80 (d, 2H), 3.51-3.38 (m, 2H), 3.11-2.94 (m, 2H), 2.39-2.19 (m, 1H), 2.06-1.94 (m, 2H), 1.67-1.49 (m, 2H), 1.22 (s, 3H), 1.19 (s, 3H); 13C NMR (75 MHz, CD3OD) δ 181.4, 163.9, 163.4, 144.7, 134.7, 132.3, 131.0, 125.9, 125.8, 122.6, 118.4, 111.3, 94.9, 87.4, 82.6, 60.2, 46.7, 45.7, 45.6, 43.3, 34.6, 28.8, 28.7, 28.6; MS (ES+) m/z 405.4 (M+1).
