To a stirred solution of 6-fluoro-2′-oxo-1′-[(2R)-tetrahydrofuran-2-ylmethyl]-1′,2′-dihydrospiro[1-benzofuran-3,3′-indole]-5-carbonitrile (0.59 g, 1.6 mol) and acetone oxime (0.35 g, 4.8 mmol) in N,N-dimethylformamide (20 mL) was added cesium carbonate (1.56 g, 4.8 mmol). The reaction mixture was stirred at ambient temperature for 19 h, then heated at 60° C. for 7 h and allowed to cool to ambient temperature. Water was added and the mixture was extracted with ethyl acetate (3×50 mL). The combined organic extracts were washed with water and brine, dried over anhydrous sodium sulfate and filtered. The filtrate was concentrated in vacuo. The residue was dissolved in a mixture of ethanol (30 mL), water (10 mL), and concentrated hydrochloric acid (2 mL) and stirred at reflux for 4 h. The mixture was allowed to cool to ambient temperature and neutralized with saturated aqueous sodium bicarbonate. The mixture was extracted with ethyl acetate (3×100 mL). The combined organic extracts were washed with water and brine, dried over anhydrous sodium sulfate and filtered. The filtrate was concentrated in vacuo. The residue was subjected to column chromatography and eluted with (ethyl acetate/hexanes (1/3)+0.1% v/v 7 N methanolic ammonia) to afford 3-amino-1′-[(2R)-tetrahydrofuran-2-ylmethyl]spiro[furo[3,2-f][1,2]benzisoxazole-5,3′-indol]-2′(1′H)-one (0.37 g, 60%): mp 116-119° C. (ethyl acetate/hexanes); 1H NMR (300 MHz, CDCl3) δ 7.35-7.32 (m, 1H), 7.13-7.02 (m, 3H), 6.09 (s, 1H), 6.84-6.81 (m, 1H), 4.91 (ABq, 2H), 4.31-4.25 (m, 1H), 4.13-4.09 (m, 2H), 3.86-3.66 (m, 4H), 2.12-1.87 (m, 4H); (ES+) m/z 377.9 (M+1).
