C[O:2][CH:3](OC)[C:4]1[S:5][CH:6]=[C:7]([C@@H:9]2[CH2:13][C@@H:12]([O:14][S:15]([CH3:18])(=[O:17])=[O:16])[CH2:11][N:10]2[C:19]([O:21][CH2:22][C:23]2[CH:28]=[CH:27][C:26]([N+:29]([O-:31])=[O:30])=[CH:25][CH:24]=2)=[O:20])[N:8]=1.C1(C)C=CC(S(O)(=O)=O)=CC=1>CC(C)=O>[CH:3]([C:4]1[S:5][CH:6]=[C:7]([C@@H:9]2[CH2:13][C@@H:12]([O:14][S:15]([CH3:18])(=[O:17])=[O:16])[CH2:11][N:10]2[C:19]([O:21][CH2:22][C:23]2[CH:28]=[CH:27][C:26]([N+:29]([O-:31])=[O:30])=[CH:25][CH:24]=2)=[O:20])[N:8]=1)=[O:2]To a solution of (2S,4R)-2-[2-(dimethoxymethyl)-thiazol-4-yl]-4-methanesulfonyloxy-1-(4-nitrobenzyloxycarbonyl)pyrrolidine (2.6 g) in acetone (100 ml) was added p-toluenesulfonic acid (0.49 g) at room temperature. After stirring under reflux for 1 hour, the mixture was evaporated. The residue was dissolved in ethyl acetate, washed in turn with saturated aqueous sodium bicarbonate and brine, and dried over magnesium sulfate. The organic layer was evaporated to give (2S,4R)-2-(2-formylthiazol-4-yl)-4-methanesulfonyloxy-1-(4-nitrobenzyloxycarbonyl)pyrrolidine (2.26 g).
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