A mixture of spiro[furo[2,3-f][1,3]benzodioxole-7,3′-indol]-2′(1′H)-one (0.30 g, 1.07 mmol) and cesium carbonate (0.56 g, 1.71 mmol) in N,N-dimethylformamide (7 mL) was stirred at ambient temperature under nitrogen for 40 min. To this mixture was added potassium iodide (0.05 g, 0.28 mmol) and (R)-(1,4-dioxan-2-yl)methyl 4-methylbenzenesulfonate (0.38 g, 1.40 mmol). The reaction was warmed to 60° C. and stirred for 2 h. The solvent was removed under reduced pressure, and the residue was suspended in ethyl acetate and filtered through Celite. The filtrate was concentrated under reduced pressure and the product was purified by flash column chromatography with dichloromethane/t-butyl methyl ether (19:1) to afford 1′-[(2S)-1,4-dioxan-2-ylmethyl]spiro[furo[2,3-f][1,3]benzodioxole-7,3′-indol]-2′(1′H)-one (0.38 g, 93%) as a colorless solid: mp 147-149° C. (ethyl acetate/hexanes); 1H NMR (300 MHz, CDCl3) (diastereomers) δ7.34-7.28 (m, 1H), 7.17 (d, J=7.2 Hz, 1H), 7.09-7.02 (m, 2H), 6.51 (s, 1H), 6.16, 6.12 (s, 1H), 5.89-5.86 (m, 2H), 4.81, 4.80 (2ABq, 2H), 3.99-3.55 (m, 8H), 3.46-3.38 (m, 1H); 13C NMR (75 MHz, CDCl3) (diastereomers) δ178.0, 177.9, 156.0, 155.9, 149.01, 148.98, 142.7, 142.6, 142.5, 142.4, 132.3, 132.2, 129.02, 128.97, 123.94, 123.87, 123.6, 119.7, 119.5, 109.6, 109.4, 103.14, 103.07, 101.64, 101.62, 93.74, 93.72, 80.5, 80.4, 73.3, 73.2, 69.4, 69.2, 66.8, 66.7, 66.53, 66.49, 58.3, 58.2, 41.9, 41.7; MS (ES+) m/z 381.9 (M+1).
