C[O:2][C:3]([C:5]1[CH:6]=[CH:7][C:8]2[CH:12]=[C:11]([CH3:13])[S:10][C:9]=2[CH:14]=1)=[O:4].[OH-].[Na+].Cl>O>[CH3:13][C:11]1[S:10][C:9]2[CH:14]=[C:5]([C:3]([OH:4])=[O:2])[CH:6]=[CH:7][C:8]=2[CH:12]=12-Methyl-benzo[b]thiophene-6-carboxylic acid methyl ester (0.83 g, 4.0 mmol) is reacted with NaOH (0.80 g, 20 mmol) in H2O (20 mL). at reflux for 2 h. The reaction is cooled to 0° C. and acidified with 1.0 M HCl to pH (3˜4). It is extracted with EtOAc (3×100 mL); dried with Na2SO4 filtered and concentrated gives the title compound (0.78 g, 4.0 mmol, quant.). 1H NMR (CDCl3): δ 2.64 (d, J=0.89 Hz, 3H), 7.06 (s, 1H), 7.71 (d, J=8.3 Hz, 1H), 8.03 (dd, J=8.3, 1.7 Hz, 1H), 8.54 (d, J=0.8 Hz, 1H) ppm. ES-MS (m/z): calcd for C10H8O2S (M−H)−: 191.2. found: 191.0.
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