To a solution of 4′-bromo-1′,2,2′,3-tetrahydrospiro[furo[2,3-g][1,4]benzodioxine-8,3′-indole] (0.30 g, 0.80 mmol) in anhydrous tetrahydrofuran (20 mL) at −98° C. was added tert-butyllithium (1.90 mL, 1.7 M solution in pentane, 3.2 mmol) and stirred for 15 min. Trimethyl borate (0.36 mL, 3.2 mmol) was added and the reaction mixture was allowed to warm to ambient temperature and stirred for 16 h. A solution of hydrogen peroxide in water (0.28 mL, 35% w/w, 3.2 mmol) was added to the reaction mixture at 0° C., and the mixture was allowed to warm to ambient temperature, stirred for 0.5 h and concentrated in vacuo. The residue was triturated with water and filtered. The resultant solid was purified by column chromatography and eluted with a 0% to 50% gradient of ethyl acetate in dichloromethane to afford 4′-hydroxy-2,3-dihydrospiro[furo[2,3-g][1,4]benzodioxine-8,3′-indol]-2′(1′H)-one (0.004 g, 2%) as a colorless solid: mp>250° C.; 1H NMR (300 MHz, DMSO-d6) δ 10.37 (s, 1H), 9.50 (s, 1H), 7.00 (dd, J=8.0, 8.0 Hz, 1H), 6.39-6.34 (m, 3H), 6.08 (s, 1H), 4.64 (ABq, 2H), 4.09 (m, 4H); 13C NMR (75 MHz, DMSO-d6) δ 179.3, 155.5, 154.1, 144.0, 143.6, 137.7, 130.1, 121.0, 116.1, 111.1, 110.5, 101.8, 98.7, 76.8, 64.6, 64.0, 57.2; MS (ES+) m/z 311.7 (M+1).
