[NH2:1][C:2]1[C:11]([N+:12]([O-])=O)=[CH:10][C:5]([C:6]([O:8][CH3:9])=[O:7])=[CH:4][C:3]=1[Br:15].[Sn](Cl)Cl.C(=O)(O)[O-].[Na+]>CO>[NH2:12][C:11]1[CH:10]=[C:5]([CH:4]=[C:3]([Br:15])[C:2]=1[NH2:1])[C:6]([O:8][CH3:9])=[O:7]A suspension of methyl 4-amino-3-bromo-5-nitrobenzoate (10 g, 36.3 mmol) and tin(II) chloride (33 g, 14.5 mmol) in methanol (100 mL) was heated to 60° C. and maintained for 4 hours. The reaction mass was cooled to ambient temperature and concentrated to obtain a residue; the residue was basified using saturated aqueous sodium bicarbonate until pH was 11 and the aqueous layer was extracted with dichloromethane (3×200 mL). The combined organic layers were washed with aqueous saturated sodium chloride (200 mL), dried over anhydrous sodium sulfate and concentrated to obtain methyl 3,4-diamino-5-bromobenzoate as an off-white solid (5 g, 58%). 1HNMR (CDCl3): δ ppm 7.74 (s, 1H), 7.35 (s, 1H), 4.18 (broad s, 2H), 3.85 (s, 3H) and 3.38-3.56 (broad s, 2H).
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