[CH3:1][O:2][C:3](=[O:16])[CH2:4][S:5][CH:6]([CH3:15])[CH2:7][C:8]([O:10]C(C)(C)C)=[O:9].FC(F)(F)C(O)=O>ClCCl>[CH3:1][O:2][C:3](=[O:16])[CH2:4][S:5][CH:6]([CH3:15])[CH2:7][C:8]([OH:10])=[O:9]1.5 g (6.0 mmol) of t-butyl 3-[(2-methoxy-2-oxoethyl)thio]butanoate (product of step 1) was stirred at room temperature with 10 mL of dichloromethane and 5 mL of trifluoroacetic acid for 6 hours, followed by distillation under reduced pressure. After addition of 40 mL of ethylacetoacetate 40 mL and washing with water, an organic layer was dried over anhydrous magnesium sulfate. The solvent was distilled off under reduced pressure and then the residue was purified by column chromatography to give 1 g (5.1 mmol) of the title compound in a yield of 85%.
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