[CH3:1][O:2][C:3]1[C:8]2[O:9][C:10]3[CH:15]=[CH:14][CH:13]=[CH:12][C:11]=3[C:7]=2[CH:6]=[CH:5][CH:4]=1.[N+:16]([O-])([OH:18])=[O:17].[OH-].[Na+].COC1C2OC3C=CC=CC=3C=2C=CC=1[N+]([O-])=O>C(O)(=O)C.O>[CH3:1][O:2][C:3]1[C:8]2[O:9][C:10]3[CH:15]=[CH:14][CH:13]=[CH:12][C:11]=3[C:7]=2[C:6]([N+:16]([O-:18])=[O:17])=[CH:5][CH:4]=1
To a solution of 4-methoxy-dibenzofuran (3.15 g; 15.89 mmol) in glacial acetic acid (50 mL), fuming nitric acid (2.6 mL; 63.50 mmol) was added dropwise. The reaction was kept at 20° C. during the addition and stirred for 3 h. Upon completion, the reaction mixture was poured carefully onto iced water; pH was adjusted to 7 by addition of 1 M sodium hydroxide, and the product was extracted in DCM. The organic layer was dried on magnesium sulfate, filtered and then concentrated. The residue was purified by flash chromatography using ethyl acetate/EP (1:19) as eluant. The first compound to come off the column was the 4-methoxy-3-nitro-dibenzofuran (270 mg, 1.11 mmol, 7%) then the title compound (1.85 g, 7.62 mmol, 48%) was obtained as a cream solid: Rf=0.13 (EtOAc-EP 1:19); mp: 155-156° C.; λmax (EtOH)/nm 239; IR (cm−1) 3092, 2917, 2851, 2042, 1876, 1630, 1568, 1506, 1438, 1396, 1342, 1297, 1274, 1239, 1205, 1159, 1129, 1091, 1002, 938, 888, 831, 812, 738, 676; 1H NMR, (300 MHz, CDCl3) δ 4.06 (3H, s, OCH3), 6.92 (1H, d, J=8 Hz), 7.18 (1H, t, J=8 Hz), 7.36 (2H, m), 8.17 (1H, d, J=8 Hz), 8.63 (1H, d, J=8 Hz); 13C NMR, (75 MHz, CDCl3) δ 56.81 (OCH3), 107.53, 111.81, 120.50 (Cq), 121.14 (Cq), 122.27, 123.71, 126.32, 129.55, 136.29 (Cq), 145.20 (Cq), 150.53 (Cq), 157.02 (Cq); MS (EI) m/z 243.1 M+; HRMS calcd for C13H9NO4 [M+H]+ 243.0526, found 243.0528.
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