Reaction Steps
A solution of 1′-[(2S)-pyrrolidin-2-ylmethyl]-5,6-dihydrospiro[benzo[1,2-b:5,4-b′]difuran-3,3′-indol]-2′(1′H)-one (0.23 g, 0.62 mmol), acetic anhydride (0.09 mL, 0.95 mmol) and triethylamine (0.17 mL, 1.2 mmol) in dichloromethane (4 mL) was stirred at ambient temperature for 40 min. The reaction was diluted with 0.2 M hydrochloric acid (50 mL) and extracted with dichloromethane (3×25 mL). The combined organic solution was dried over sodium sulfate, filtered and concentrated under reduced pressure. Purification by flash column chromatography with dichloromethane/diethyl ether (4:1) afforded 1′-{[(2S)-1-acetylpyrrolidin-2-yl]methyl}-5,6-dihydrospiro[benzo[1,2-b:5,4-b′]difuran-3,3′-indol]-2′(1′H)-one (0.21 g, 84%) as an off-white solid: mp 103-108° C. (hexanes); 1H NMR (300 MHz, CDCl3) (diastereomers) δ 7.54, 7.53 (d, J=7.8 Hz, 1H), 7.35, 7.34 (dd, J=8.1, 7.7 Hz, 1H), 7.15 (d, J=7.5 Hz, 1H), 7.06 (dd, J=7.5 Hz, 1H), 6.49, 6.46 (s, 1H), 6.42, 6.41 (s, 1H), 4.91, 4.90 (d, J=9.0 Hz, 1H), 4.68, 4.67 (d, J=9.0 Hz, 1H), 4.54, 4.53 (t, J=8.7 Hz, 2H), 4.49-4.42 (m, 1H), 3.95-3.80 (m, 2H), 3.61-3.54 (m, 1H), 3.46-3.36 (m, 1H), 3.00, 2.99 (t, J=8.6 Hz, 2H), 2.26-1.76 (m, 4H), 2.11-2.08 (s, 3H); 13C NMR (75 MHz, CDCl3) (diastereomers) δ 178.49, 178.47, 170.2, 161.9, 161.8, 161.5, 161.4, 142.6, 142.4, 132.5, 132.3, 129.36, 129.33, 123.8, 123.7, 123.6, 123.5, 120.4, 120.2, 120.0, 119.9, 119.2, 118.7, 110.01, 109.96, 93.4, 93.2, 80.9, 80.8, 72.5, 57.9, 55.0, 54.8, 47.9, 41.5, 41.2, 29.2, 29.1, 28.0, 27.8, 23.9, 22.92, 22.90; MS (ES+) m/z 405.1 (M+1).
