Reaction Steps
To a stirred solution of 1′-[(2S)-2-hydroxypropyl]-5,6-dihydrospiro[benzo[1,2-b:5,4-b′]difuran-3,3′-indol]-2′(1′H)-one (0.19 mg, 0.56 mmol) in anhydrous tetrahydrofuran (10 mL) was added sodium hydride (60% dispersion in mineral oil, 0.03 g, 0.71 mmol). The solution was stirred at ambient temperature for 30 min, then benzylbromide (0.14 g, 0.84 mmol) was added. The reaction mixture was stirred for 16 h. The solution was cooled to ambient temperature, filtered and concentrated in vacuo to dryness. The residue was purified by flash chromatography with ethyl acetate in hexanes (25%) to afford 1′-[(2S)-2-(benzyloxy)propyl]-5,6-dihydrospiro[benzo[1,2-b:5,4-b′]difuran-3,3′-indol]-2′(1′H)-one (0.20 g, 77%) as a colorless solid: mp 45-47° C.; 1H NMR (300 MHz, CDCl3) (diastereomers) δ7.30-6.97 (m, 9H), 6.38 (s, 1H), 6.33 (d, J=36.0 Hz, 1H), 4.84 (dd, J=21.7, 8.9 Hz, 1H), 4.68-4.55 (m, 2H), 4.49 (dt, J=8.6, 0.8 Hz, 2H), 4.40 (dd, J=12.0, 3.8 Hz, 1H), 4.01-3.83 (m, 2H), 3.80-3.68 (m, 1H), 2.88 (t, J=8.6 Hz, 3H); 13C NMR (75 MHz, CDCl3) (diastereomers) δ178.1 (2), 161.7 (2), 161.3 (2), 143.0 (2), 138.3 (2), 132.7, 128.6, 128.3 (2), 127.5 (2), 127.3, 123.6 (2), 123.2, 120.3 (2), 119.8 (2), 118.9 (2), 109.7 (2), 93.2, 80.7 (2), 73.2, 72.8, 72.4, 70.9, 70.7, 57.6, 46.1 (2), 29.0 (2), 17.7 (2); MS (ES+) m/z 428.0 (M+23).
