[N+:1]([C:4]1[CH:5]=[C:6]([NH2:13])[C:7](=[CH:11][CH:12]=1)[C:8]([OH:10])=[O:9])([O-:3])=[O:2].[Si](C=[N+]=[N-])(C)(C)[CH3:15]>C1C=CC=CC=1.CO>[CH3:15][O:9][C:8](=[O:10])[C:7]1[C:6](=[CH:5][C:4]([N+:1]([O-:3])=[O:2])=[CH:12][CH:11]=1)[NH2:13]To a solution of 4-nitro-anthranilic acid (2.200 g, 10.9 mmol, 1 eq) in benzene/methanol (4/1) (100 mL) was added TMSCHN2 (2M in hexanes) (12 mL, 24 mmol, 2.2 eq). The reaction was stirred at room temperature for 30 minutes and then concentrated in vacuo. The residue was purified by flash chromatography using ethyl acetate/hexanes (20/80) to afford 4-nitro-anthranilic acid methyl ester (1.841 g, 86%) as a bright yellow solid. 1H NMR (300 MHz, CDCl3); δ 8.00 (d, 1H), 7.50 (d, 1H), 7.40 (dd, 1H), 3.92 (s, 3H).
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