Reaction Steps
To a stirred solution of ethyl {3-[(2′-oxo-5,6-dihydrospiro[benzo[1,2-b:5,4-b′]difuran-3,3′-indol]-1′(2′H)-yl)methyl]phenoxy}acetate (0.46 g, 0.98 mmol) in a mixture of tetrahydrofuran (30 mL) and water (15 mL) was added lithium hydroxide monohydrate (0.32 g, 2.3 mmol) at ambient temperature. The mixture was stirred at ambient temperature for 16 h. The mixture was concentrated in vacuo to a small volume, diluted with water (15 mL), washed with diethyl ether (60 mL), and acidified with 37% hydrochloric acid to pH 1. A white precipitate was formed. The mixture was extracted with ethyl acetate (3×60 mL). The combined organic solution was washed with water (30 mL), brine (50 mL), dried over anhydrous magnesium sulfate, filtered, and concentrated in vacuo to afford {3-[(2′-oxo-5,6-dihydrospiro[benzo[1,2-b:5,4-b′]difuran-3,3′-indol]-1′(2′H)-yl)methyl]phenoxy}acetic acid (0.41 g, 95%): mp 95-96° C.; 1H NMR (300 MHz, CDCl3) 7.33-7.14 (m, 3H), 7.07-6.97 (m, 2H), 6.92 (br s, 1H), 6.88-6.77 (m, 2H), 6.48 (s, 1H), 6.42 (s, 1H), 5.08-4.95 (m, 2H), 4.88-4.79 (m, 1H), 4.74-4.67 (m, 1H), 4.63 (s, 2H), 4.57-4.48 (m, 2H), 3.09-2.89 (m, 2H); 13C NMR (75 MHz, CDCl3) δ 178.2, 172.6, 161.8, 161.3, 157.9, 141.9, 137.6, 132.6, 130.1, 128.8, 123.9, 123.6, 120.9, 120.0, 118.9, 113.9, 113.7, 113.7, 109.3, 93.2, 80.5, 72.4, 64.7, 57.8, 44.0, 29.0; MS (ES+) m/z 444.0 (M+1).
