[NH2:1][C:2]1[CH:10]=[CH:9][C:8]([N+:11]([O-:13])=[O:12])=[CH:7][C:3]=1[C:4]([OH:6])=[O:5].CO[CH:16]1[CH2:20][CH2:19][CH:18](OC)O1>C(O)(=O)C>[N+:11]([C:8]1[CH:9]=[CH:10][C:2]([N:1]2[CH:16]=[CH:20][CH:19]=[CH:18]2)=[C:3]([CH:7]=1)[C:4]([OH:6])=[O:5])([O-:13])=[O:12]A mixture of 2-amino-5-nitrobenzoic acid (475 mg), 2,5-dimethoxytetrahydrofuran (345 mg) and acetic acid (10 ml) was heated under reflux for 3 hours and then concentrated at reduced pressure. Brine was added to the resulting residue and the mixture was extracted with ethyl acetate. The organic layer was dried with anhydrous sodium sulfate and then concentrated at reduced pressure. The resulting residue was purified by silica gel column chromatography (eluent; ethyl acetate:n-hexane=1:1) to give the titled compound (yield, 73%).
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