B(Br)(Br)Br.[CH2:5]([O:7][C:8]([C:10]1[CH:27]=[CH:26][C:13]2[S:14][C:15]([C:17]3[CH:22]=[CH:21][C:20]([O:23]C)=[CH:19][C:18]=3[CH3:25])=[CH:16][C:12]=2[CH:11]=1)=[O:9])[CH3:6].O.C(Cl)(=O)C>ClCCl.C(OCC)(=O)C>[CH2:5]([O:7][C:8]([C:10]1[CH:27]=[CH:26][C:13]2[S:14][C:15]([C:17]3[CH:22]=[CH:21][C:20]([OH:23])=[CH:19][C:18]=3[CH3:25])=[CH:16][C:12]=2[CH:11]=1)=[O:9])[CH3:6]A 0° C. solution of boron tribromide (1M in dichloromethane, 1.29 mmol; 1.29 mL) is added under nitrogen atmosphere to a solution of 2-(4-methoxy-2-methyl-phenyl)-benzo[b]thiophene-5-carboxylic acid ethyl ester (1.07 mmol; 350 mg) in anhydrous dichloromethane (4.00 mL) and the mixture is stirred at room temperature for 4 h. Water and ethyl acetate are added. The aqueous layer is separated and the organic layer is dried (Na2SO4), filtered, and concentrated under reduced pressure. The residue is dissolved in ethanol (5 mL) and acetyl chloride (3.48 mmol, 0.25 mL) is added. The mixture is stirred at reflux for 5 h. The solvent is removed and the residue is chromatographed (5-20% EtOAc in hexanes) to yield the title compound (145 mg, 40%) as a white solid. LC-ES/MS m/e 313 (M+1).
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