C[O:2][C:3](=[O:21])[C:4]1[CH:9]=[CH:8][C:7]([O:10][CH2:11][C:12]2[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=2)=[C:6]([N+:18]([O-:20])=[O:19])[CH:5]=1.CO.[OH-].[K+].Cl>O1CCCC1>[CH2:11]([O:10][C:7]1[CH:8]=[CH:9][C:4]([C:3]([OH:21])=[O:2])=[CH:5][C:6]=1[N+:18]([O-:20])=[O:19])[C:12]1[CH:13]=[CH:14][CH:15]=[CH:16][CH:17]=1A solution the crude 4-benzyloxy-3-nitro-benzoic acid methyl ester from the previous step in tetrahydrofurane (150 mL) and MeOH (600 mL) was treated with KOH 3N (152 mL) and stirred at room temperature for 18 hours. The mixture was acidified with HCl 3N. The precipitate thus formed was filtered, washing with MeOH/water 1:1 and dried under vacuum. 4-Benzyloxy-3-nitro-benzoic acid (42 g, 95% over two steps) was obtained as a white solid, which was used crude in the following reaction.
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