[C:1]1([NH:7]N)[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.[C:9]([C:12]1[O:13][C:14]2[CH:20]=[CH:19][CH:18]=[CH:17][C:15]=2[CH:16]=1)(=O)[CH3:10]>C(O)C.C(O)(=O)C>[CH:4]1[CH:5]=[C:6]2[CH:10]=[C:9]([C:12]3[O:13][C:14]4[C:15](=[CH:17][CH:18]=[CH:19][CH:20]=4)[CH:16]=3)[NH:7][C:1]2=[CH:2][CH:3]=1Phenylhydrazine (97%; 6.3 ml, 1 eq) is introduced into a solution of 2-acetylbenzofuran (10 g, 1 eq) in ethanol (25 ml). After adding 20 drops of glacial acetic acid, the mixture is stirred at 80° C. for 1 h. Subsequently, the solvent is distilled off. The residue is introduced gradually into polyphosphoric acid (100 g), heated to 120° C. and stirred for 1 h. The reaction output is added cautiously to ice-water and neutralized with 2M NaOH. The precipitate is filtered off and washed with distilled water. The residue is dried under reduced pressure. After recrystallization in ethyl acetate/n-hexane, 7.0 g are obtained. Yield: 48%
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