To a solution of 1-(2-cyclopropylethyl)-3-hydroxy-3-(6-hydroxy-1,3-benzodioxol-5-yl)-1,3-dihydro-2H-indol-2-one (2.22 g, 6.27 mmol) in dichloromethane (30.0 mL) was added trifluoroacetic acid (2.12 g, 18.8 mmol) and triethylsilane (2.14 g, 18.8 mmol). The brown solution was stirred at ambient temperature for 0.5 h and concentrated in vacuo to dryness. The residue was diluted with dichloromethane (100 mL), washed with water (3×50.0 mL), dried over anhydrous sodium sulfate and filtered. The filtrate was concentrated in vacuo to dryness. The residue was subjected to column chromatography eluting with ethyl acetate/hexane (20/80) to give the title compound (1.69 g, 80%) as a brown solid: 1H NMR (300 MHz, CDCl3) δ 9.21-9.10 (br, 1H), 7.38-7.30 (m, 2H), 7.16 (t, 1H), 6.96 (d, 1H), 6.63 (s, 1H), 6.33 (s, 1H), 5.84 (dd, 2H), 5.01 (s, 1H), 3.87-3.72 (m, 2H), 1.66-1.46 (m, 2H), 0.69-0.59 (m, 1H), 0.43-0.30 (m, 2H), 0.09-0.06 (m, 2H); 13C NMR (75 MHz, CDCl3) δ 178.8, 151.3, 147.6, 144.1, 141.5, 128.7, 126.2, 123.1, 115.2, 109.5, 109.4, 106.5, 101.5, 101.2, 47.4, 40.5, 32.2, 8.6, 4.3, 4.2; MS (ES+) m/z 338.3 (M+1).
