[CH2:1]([O:3][C:4]([C:6]1[N:7]=[C:8]([N:11]2[CH2:15][CH2:14][C@@H:13](OS(C)(=O)=O)[CH2:12]2)[S:9][CH:10]=1)=[O:5])[CH3:2].[C:21]([O-:24])(=S)[CH3:22].[K+]>CN(C)C=O>[C:21]([C@H:13]1[CH2:14][CH2:15][N:11]([C:8]2[S:9][CH:10]=[C:6]([C:4]([O:3][CH2:1][CH3:2])=[O:5])[N:7]=2)[CH2:12]1)(=[O:24])[CH3:22]To a solution of (3R)-1-(4-ethoxycarbonyl-1,3-thiazol-2-yl)-3-methanesulfonyloxypyrrolidine (1.0 g, 3.12 mmol) (obtained as described in Reference Example 20(1)) in dimethylformamide (30 ml) was added potassium thioacetate (919 mg, 9.36 mmol) at room temperature. The mixture was stirred in an oil bath (80° C.) for 5.5 hours. After checking the completion of the reaction, the reaction mixture was partitioned between ethyl acetate and 10% aqueous sodium chloride solution. The organic layer was washed successively with saturated aqueous sodium hydrogencarbonate solution and saturated aqueous sodium chloride solution, dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The residue was purified by chromatography on a silica gel column using toluene:acetonitrile (3:1→1:1) as the eluant to afford (3S)-3-acetyl-1-(4-ethoxycarbonyl-1,3-thiazol-2-yl)pyrrolidine (877 mg, yield 99%) as a pale brown solid.
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