[C:1](=[O:4])([O-])[O-:2].[K+].[K+].[OH:7][C:8]1[CH:18]=[CH:17][C:11]([C:12]([O:14][CH2:15][CH3:16])=[O:13])=[CH:10][CH:9]=1.O>[N+](C1C=CC=CC=1)([O-])=O.[Cu]>[CH2:15]([O:14][C:12]([C:11]1[CH:10]=[CH:9][C:8]([O:7][C:8]2[CH:18]=[CH:17][CH:11]=[CH:10][C:9]=2[C:1]([OH:2])=[O:4])=[CH:18][CH:17]=1)=[O:13])[CH3:16]Potassium carbonate (14 g) was added to a solution of 2-indobenzoic acid (50 g) in nitrobenzene (50 ml) at 140°-150° C. with stirring. The mixture was stirred for an additional 10 minutes after the addition. Then, ethyl 4-hydroxybenzoate (33.5 g), potassium carbonate (28 g) and copper (3 g) were added. The mixture was stirred at 150°-160° C. for 30 minutes and allowed to cool. After the addition of water, the mixture was filtered and the filtrate was acidified with concentrated hydrochloric acid. The precipitate was collected and recrystallized from dilute ethanol to give the title compound (42 g, 72%), m.p. 152°-153° C.
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