To a stirred solution of 2H-[1,4]dioxino[2,3-f]indole-7,8(3H,6H)-dione (2.05 g, 10.0 mmol) in dry N,N-dimethylformamide (100 mL) was added cesium carbonate (4.4 g, 12.0 mmol) at ambient temperature. The dark mixture was stirred for 1 h, followed by the addition of (R)-(tetrahydrofuran-2-yl)methyl 4-methylbenzenesulfonate (3.07 g, 12.0 mmol) in one portion and potassium iodide (0.66 g, 4.0 mmol). The dark mixture was stirred at 70° C. for 16 h. The mixture was poured into 5% hydrochloric acid solution (300 mL) and extracted with ethyl acetate. The organic layer was separated, dried over magnesium sulfate, filtered and evaporated. The residue was purified by flash column chromatography with ethyl acetate in hexanes (30 to 50% gradient) to afford 6-[(2R)-tetrahydrofuran-2-ylmethyl]-2,3-dihydro-6H-[1,4]dioxino[2,3-f]indole-7,8-dione (0.59 g, 20%): MS (ES+) m/z 290.2 (M+1).
