Reaction Steps
A round bottom flask was charged with 4-[(2′-oxo-5,6-dihydrospiro[benzo[1,2-b:5,4-b′]difuran-3,3′-indol]-1′(2′H)-yl)methyl]benzonitrile (0.50 g, 1.27 mmol), sodium azide (0.21 g, 3.17 mmol), and triethylamine hydrochloride (0.45 g, 3.17 mmol) in toluene (20 mL). The reaction mixture was refluxed under argon for 24 h. After cooling to ambient temperature, the product was extracted with water. 36% hydrochloric acid was added dropwise to the aqueous layer. The solid was filtrated and dried under reduced pressure to afford 1′-[4-(1H-tetrazol-5-yl)benzyl]-5,6-dihydrospiro[benzo[1,2-b:5,4-b′]difuran-3,3′-indol]-2′(1′H)-one (0.38 g, 58%); 1H NMR (300 MHz, CDCl3) δ8.02 (d, J=8.0 Hz, 2H), 7.55 (d, J=8.0 Hz, 2H), 7.22 (t, J=7.6 Hz, 1H), 7.16 (d, J=7.6 Hz, 1H), 7.05-6.94 (m, 2H), 6.47 (s, 1H), 6.40 (s, 1H), 5.01 (ABq, 2H), 4.79 (ABq, 2H), 4.53-4.38 (m, 2H), 3.03-2.82 (m, 2H); 13C NMR (75 MHz, CD3OD) δ177.6, 161.6, 161.2, 142.5, 140.1, 132.6, 129.1, 128.6, 127.9, 124.2, 123.6, 120.8, 120.4, 119.4, 109.8, 92.9, 80.3, 72.5, 57.4, 43.3, 28.8; MS (ES+) m/z 437.9 (M+1).
