To a solution of 1,3-benzodioxol-5-ol (12.8 g, 92.9 mmol) in tetrahydrofuran (200 mL) was added isopropylmagnesium chloride solution (50.7 mL, 101 mmol, 2.0 M in ether) at 0° C. The reaction mixture was stirred at 0° C. for 0.5 h, upon which time the colorless precipitate was formed. After the solvent was removed under reduced pressure, the residue was dissolved in methylene chloride (100 mL) and added to a solution of 4-bromo-1-pentyl-1H-indole-2,3-dione (25.0 g, 84.5 mmol) in dichloromethane (100 mL) via a canula over 10 min at 0° C. The reaction mixture was stirred at ambient temperature for 16 h, quenched with saturated ammonium chloride solution (100 mL) and the organic layer was separated. The aqueous layer was extracted with dichloromethane (100 mL). The combined organic layers was washed with brine, 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 to give the title compound (34.9 g, 97%) as a brown gummy material: 1H NMR (300 MHz, DMSO-d6) δ 8.95 (s, 1H), 7.29-7.21 (m, 2H), 6.88-6.81 (m, 1H), 6.55, (s, 1H), 6.14 (s, 1H), 5.86 (dd, 2H), 4.24 (s, 1H), 3.70-3.52 (m, 2H), 1.69-1.55 (m, 2H), 1.31-1.24 (m, 4H), 0.83 (t, 3H); 13C NMR (75 MHz, DMSO-d6) δ 177.6, 152.6, 149.1, 144.8, 141.2, 131.7, 127.7, 127.6, 121.0, 113.8, 108.3, 106.7, 101.7, 101.4, 80.5 40.5, 28.8, 26.7 22.2, 13.9.
