[Br:1][C:2]1[C:7]([C:8]([O:10][CH3:11])=[O:9])=[C:6]([N+:12]([O-])=O)[C:5]([NH:15][CH:16]([CH2:18]C(OCC)=O)[CH3:17])=[CH:4][CH:3]=1.[Sn](Cl)Cl.[C:27](OCC)(=[O:29])C.C(=O)([O-])O.[Na+]>C(O)C>[Br:1][C:2]1[C:7]([C:8]([O:10][CH3:11])=[O:9])=[C:6]2[C:5]([NH:15][C:16]([CH3:17])([CH3:18])[C:27](=[O:29])[NH:12]2)=[CH:4][CH:3]=1Methyl 6-bromo-3-[(2-ethoxycarbonyl)propan-2-yl]amino-2-nitrobenzoate (Reference Compound No. 1-(5), 105 mg, 0.26 mmol) was dissolved in anhydrous ethanol (4.5 mL), tin (II) chloride (247 mg, 1.30 mmol) was added thereto, and then the reaction mixture was refluxed for 5 hours. After cooling down, ethyl acetate (25 mL) was added to the reaction mixture, the mixture was neutralized with aqueous sodium hydrogen carbonate solution, and then filtered on celite. After the filtrate was partitioned, the water layer was extracted with ethyl acetate (10 mL, twice), the combined organic layer was washed with water (50 mL, twice) and saturated brine (50 mL) successively, dried over anhydrous magnesium sulfate, and then the solvent was removed under reduced pressure. The obtained residue was purified by silica gel column chromatography (hexane-ethyl acetate) to give the titled reference compound (56.3 mg) as a pale yellow solid. (Yield 70%)
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