To a stirred mixture of 1′-[(6-methoxypyridin-3-yl)methyl]-2,3-dihydrospiro[furo[2,3-g][1,4]benzodioxine-8,3′-indol]-2′(1′H)-one (0.24 g, 0.58 mmol), sodium iodide (0.29 g, 1.9 mmol), and water (2 drops) in acetonitrile (5 mL) was added chlorotrimethylsilane (0.23 mL, 1.8 mmol). The reaction mixture was stirred at ambient temperature for 16 h. Further, sodium iodide (0.14 g, 0.95 mmol) and chlorotrimethylsilane (0.12 mL, 0.95 mmol) were added and the reaction mixture was stirred at ambient temperature for 24 h. Further, sodium iodide (0.29 g, 1.9 mmol) and chlorotrimethylsilane (0.23 mL, 1.8 mmol) were added and the reaction mixture was stirred at ambient temperature for 5 days. A solution of sodium bisulfite (0.51 g, 4.9 mmol) in water (30 mL) and ethyl acetate (150 mL) were added. The layers were separated and the organic layer was washed with brine (2×50 mL), dried over anhydrous magnesium sulfate, filtered and concentrated in vacuo. The residue was triturated with diethyl ether and the crude product was purified by preparative thin layer chromatography and eluted with 30% acetone in dichloromethane to afford 1′-[(6-oxo-1,6-dihydropyridin-3-yl)methyl]-2,3-dihydrospiro[furo[2,3-g][1,4]benzodioxine-8,3′-indol]-2′(1′H)-one (0.15 g, 63%) as a colorless solid: mp 249-250° C.; 1H NMR (300 MHz, CDCl3) δ7.61-7.46 (m, 2H), 7.31-7.21 (m, 1H), 7.20-7.14 (m, 1H), 7.09-7.02 (m, 1H), 6.86-6.81 (m, 1H), 6.66-6.59 (m, 1H), 6.50 (s, 1H), 6.15 (s, 1H), 4.92-4.60 (m, 4H), 4.24-4.06 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 177.7, 164.4, 155.2, 144.7, 142.2, 141.4, 138.3, 133.5, 132.2, 129.0, 124.2, 123.8, 120.9, 120.7, 115.8, 111.4, 108.7, 99.5, 80.0, 64.5, 63.9, 58.0, 40.6; MS (ES+) m/z 403.0 (M+1).
