[CH3:1][O:2][C:3]1[C:8]([C:9]#[N:10])=[CH:7][C:6]2[C:11]3([CH2:30][O:31][C:5]=2[CH:4]=1)[C:19]1[C:14](=[CH:15][CH:16]=[CH:17][CH:18]=1)[N:13](CC1C=CC(OC)=CC=1)[C:12]3=[O:29].FC(F)(F)S(O)(=O)=O>ClCCl.FC(F)(F)C(O)=O>[CH3:1][O:2][C:3]1[C:8]([C:9]#[N:10])=[CH:7][C:6]2[C:11]3([CH2:30][O:31][C:5]=2[CH:4]=1)[C:19]1[C:14](=[CH:15][CH:16]=[CH:17][CH:18]=1)[NH:13][C:12]3=[O:29]To a stirred solution of 6-methoxy-1′-(4-methoxybenzyl)-2′-oxo-1′,2′-dihydrospiro[1-benzofuran-3,3′-indole]-5-carbonitrile (0.50 g, 1.2 mmol) in dichloromethane (5 mL) and trifluoroacetic acid (5 mL) was added trifluoromethanesulfonic acid (1.0 mL, 11 mmol). The reaction mixture was stirred at ambient temperature for 18 h and concentrated in vacuo. The residue was basified with saturated aqueous sodium bicarbonate and extracted with ethyl acetate. The organic phase was washed with water and brine, dried over anhydrous sodium sulfate and filtered. The filtrate was concentrated in vacuo. The residue was purified by column chromatography to afford 6-methoxy-2′-oxo-1′,2′-dihydrospiro[1-benzofuran-3,3′-indole]-5-carbonitrile (0.34 g, 96%): mp 185-186° C.; 1H NMR (300 MHz, CDCl3) δ 8.46 (s, 1H), 7.30-7.25 (m, 1H), 7.11-7.03 (m, 2H), 6.97-6.94 (m, 2H), 6.56 (s, 1H), 4.91 (ABq, 2H), 3.90 (s, 3H); MS (ES+) m/z 292.9 (M+1).
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