[OH:1][C:2]1[CH:13]=[CH:12][C:5]2[S:6][CH:7]=[C:8]([C:9]([OH:11])=[O:10])[C:4]=2[CH:3]=1.SC1C=C[C:18]([OH:21])=[CH:17]C=1.N1C=CC=CC=1.O>C(OC(=O)C)(=O)C>[C:18]([O:1][C:2]1[CH:13]=[CH:12][C:5]2[S:6][CH:7]=[C:8]([C:9]([OH:11])=[O:10])[C:4]=2[CH:3]=1)(=[O:21])[CH3:17]5-Hydroxybenzo[b]thiophene-3-carboxylic acid (11) (1,140 mg) prepared in above (1) was dissolved in acetic anhydride (2 ml), pyridine (4 ml). After 3 hours, water was added and the mixture was continuously stirred under ice-cooling for 1.5 hours. The deposited crystals were filtered, washed with water and dried to provide 1,349 mg of the title compound (12). Yield: 97.3% mp 239-240° C.
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