Reaction Steps
To a cooled (0° C.) suspension of sodium hydride (60% w/w in mineral oil, 0.16 g, 3.7 mmol) in anhydrous N,N-dimethylformamide (30 mL) was added 2,3-dihydrospiro[furo[2,3-g][1,4]benzodioxine-8,3′-indol]-2′(1′H)-one (0.99 g, 3.39 mmol), followed by ethyl chloroformate (0.35 mL, 3.7 mmol). The reaction mixture was stirred at ambient temperature for 18 h and was concentrated in vacuo. The residue was purified by column chromatography and eluted with a 5% to 66% gradient of ethyl acetate in hexanes to afford ethyl 2′-oxo-2,3-dihydrospiro[furo[2,3-g][1,4]benzodioxine-8,3′-indole]-1′(2′H)-carboxylate (0.68 g, 55%) as a colourless solid: mp 198-200° C. (hexanes/ethyl acetate); 1H NMR (300 MHz, CDCl3) δ7.96 (d, J=7.7 Hz, 1H), 7.39-7.34 (m, 1H), 7.19-7.18 (m, 2H), 6.50 (s, 1H), 6.27 (s, 1H), 4.93 (d, J=9.1 Hz, 1H), 4.63 (d, J=9.1 Hz, 1H), 4.49 (q, J=7.1 Hz, 2H), 4.21-4.18 (m, 2H), 4.13-4.10 (m, 2H) 1.45 (t, J=7.1 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ175.7, 155.1, 150.8, 144.9, 138.7, 138.4, 130.7, 129.2, 125.5, 123.8, 121.0, 115.2, 111.7, 99.4, 80.8, 64.5, 63.9, 63.7, 58.6, 14.2; MS (ES+) m/z 367.7 (M+1).
