[CH3:1][O:2][C:3]1[CH:4]=[C:5]([CH2:12][C:13]([OH:15])=[O:14])[CH:6]=[CH:7][C:8]=1[N+:9]([O-:11])=[O:10].[CH3:16]O>OS(O)(=O)=O>[CH3:1][O:2][C:3]1[CH:4]=[C:5]([CH2:12][C:13]([O:15][CH3:16])=[O:14])[CH:6]=[CH:7][C:8]=1[N+:9]([O-:11])=[O:10]A solution of 2-(3-methoxy-4-nitrophenyl)acetic acid (4.6 g, 21.78 mmol) and concentrated H2SO4 (2 drops) in methanol (200 mL) was heated to reflux for 3 hours. The mixture was allowed to cool to room temperature then the solvents were removed under reduced pressure. The residue was partitioned between water (100 mL) and EtOAc (100 mL), then the separated organic layer was washed with sodium bicarbonate solution (100 mL), brine (200 mL), dried (Na2SO4) and evaporated under reduced pressure to give the title compound (4.5 g, 92%) as a solid.
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