S(Cl)(Cl)=O.[CH3:5][O:6][C:7]1[C:8]([N+:18]([O-:20])=[O:19])=[C:9]([CH:13]=[CH:14][C:15]=1[O:16][CH3:17])C(O)=O.[N-:21]=[N+]=[N-].[Na+].CCCCCC>ClCCCl.O.C(OCC)(=O)C>[CH3:5][O:6][C:7]1[C:8]([N+:18]([O-:20])=[O:19])=[C:9]([NH2:21])[CH:13]=[CH:14][C:15]=1[O:16][CH3:17]
Thionyl chloride (10 mL, 137.4 mmol, 4.98 eq) is added at room temperature to a stirred solution of 3,4-dimethoxy-2-nitro-benzoic acid (6.26 g, 27.6 mmol, 1.0 eq) in 1,2-dichloroethane (100 mL). The reaction mixture is heated at 82° C. for 2 hours, then solvent is removed and the resulting crude acid chloride is dissolved in acetone (50 mL), cooled down to 5° C. before the addition of a solution of sodium azide (10.0 g, 154.0 mmol, 5.58 eq) in water (20 mL). After 1 hour stirring, the reaction mixture is poured into water (300 ml), the resulting white precipitate of acyl azide is filtered, washed with water, dissolved in acetic acid (300 mL) and water (30 mL). The mixture is heated at 118° C. for 2 hours, then solvents are evaporated, the residue is taken in warm ethanol and filtered. The filtrate is concentrated and the residue is purified by column chromatography (silica gel, eluent: hexane: ethyl acetate, 10:1 to 5:1, v/v) to afford 3,4-dimethoxy-2-nitro-phenylamine as a red solid (3.5 g, 64% yield).
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