Reaction Steps
A solution of 2-((2′-oxo-6H-spiro[benzofuro[6,5-d][1,3]dioxole-7,3′-indoline]-1′-yl)methyl)oxazole-4-carboxylic acid (0.41 g, 1.0 mmol), N-hydroxybenzotriazole (0.20 g, 1.5 mmol) and 1-ethyl-3-(3-dimethyllaminopropyl)carbodiimide hydrochloride (0.29 g, 1.5 mmol) in dichloromethane (10 mL) was stirred for 30 min, followed by the addition of cyclopropylamine (0.8 mL). The solution was stirred at ambient temperature for 16 h, diluted with dichloromethane (100 mL), washed with distilled water (2×50 mL), dried over magnesium sulfate, filtered and concentrated in vacuo to dryness. The residue was purified by flash chromatography with ethyl acetate in hexanes (gradient: 50% to 75%) to afford N-(1-methylethyl)-2-[(2′-oxospiro[furo[2,3-f][1,3]benzodioxole-7,3′-indol]-1′(2′H)-yl)methyl]-1,3-oxazole-4-carboxamide (0.40 g, 91%) as a colorless solid: mp 188-191° C.; 1H NMR (300 MHz, CDCl3) δ8.14 (s, 1H), 7.28-7.22 (m, 1H), 7.19 (d, J=6.8 Hz, 1H), 7.07 (dd, J=7.4, 7.4 Hz, 1H), 6.85 (d, J=7.7 Hz, 2H), 6.49 (s, 1H), 6.16 (s, 1H), 5.85 (ABq, 2H), 5.04 (ABq, 2H), 4.81 (ABq, 2H), 2.82 (m, 1H), 0.85-0.77 (m, 2H), 0.64-0.58 (m, 2H); 13C NMR (75M Hz, CDCl3) δ177.2, 161.3, 158.1, 155.8, 149.0, 142.4, 141.8, 141.0, 136.6, 132.0, 129.1, 124.15, 124.10, 119.2, 108.6, 103.0, 101.6, 93.7, 80.2, 58.2, 37.1, 22.3, 6.60, 6.55; MS (ES+) m/z 446.2 (M+1).
