[CH3:1][C:2]1([CH3:14])[S:6](=[O:8])(=[O:7])[C:5]2[CH:9]=[CH:10][CH:11]=[CH:12][C:4]=2[C:3]1=[O:13].[BH4-].[Na+]>C(O)C>[CH3:1][C:2]1([CH3:14])[S:6](=[O:8])(=[O:7])[C:5]2[CH:9]=[CH:10][CH:11]=[CH:12][C:4]=2[CH:3]1[OH:13]To a solution of 2,2-dimethyl-1,1-dioxo-1,2-dihydro-llambda*6*-benzo[b]thiophen-3-one (240 mg, 1.14 mmol) in ethanol (30 mL) at 0° C. is added NaBH4 (43 mg, 1.14 mmol). The reaction is placed at room temperature and permitted to stir for one hour. The reaction is quenched with saturated aqueous NH4Cl, and concentrated to near dryness. The resulting residue is diluted with ethyl acetate and washed with brine, dried with Na2SO4, filtered, and concentrated. The resulting residue is purified by silica gel flash chromatography (ethyl acetate-heptane, 0:1 to 1:0) to provide 2,2-dimethyl-1,1-dioxo-2,3-dihydro-1H-1lambda*6*-benzo[b]thiophen-3-ol; MS: (ESI) m/z 213 (M+H)+.
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