To a suspended mixture of 7′-bromospiro[furo[2,3-f][1,3]benzodioxole-7,3′-indol]-2′(1′H)-one (0.44 g, 1.2 mmol) and zinc cyanide (0.28 g, 2.4 mmol) in anhydrous N,N-dimethylformamide (12 mL) was added tetrakis(triphenylphosphine)palladium (0.14 g, 0.12 mmol). The reaction mixture was refluxed for 3 h. The solid was filtered and washed with ethyl acetate (40 mL). The filtrate was concentrated in vacuo to dryness. The residue was purified by column chromatography with ethyl acetate in hexanes (20% to 30% gradient) to afford 2′-oxo-1′,2′-dihydrospiro[furo[2,3-f][1,3]benzodioxole-7,3′-indole]-7′-carbonitrile (0.28 g, 76%) as a colorless solid: mp 205-207° C.; 1H NMR (300 MHz, DMSO-d6) δ11.55 (s, 1H), 7.62 (dd, J=8.0 Hz, 1.1 Hz, 1H), 7.41 (d, J=7.0 Hz, 1H), 7.12-7.07 (m, 1H), 6.69 (s, 1H), 6.44 (s, 1H), 5.93 (dd, J=3.4, 0.8 Hz, 2H), 4.78 (d, J=9.5 Hz, 1H), 4.67 (d, J=9.5 Hz, 1H); 13C NMR (75 MHz, DMSO-d6) δ178.4, 155.4, 148.3, 145.2, 141.7, 133.8, 131.6, 128.3, 122.5, 118.9, 115.9, 103.2, 101.3, 93.1, 92.6, 79.6, 57.5; MS (ES+) m/z 307.3 (M+1).
