[C:1]([O:5][C:6]([NH:8][CH:9]1[CH2:12][NH:11][CH2:10]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].Br[C:14]1[S:15][C:16]([C:19]([O:21][CH2:22][CH3:23])=[O:20])=[CH:17][N:18]=1.C(N(C(C)C)CC)(C)C>CN(C=O)C.C(OCC)(=O)C>[C:1]([O:5][C:6]([NH:8][CH:9]1[CH2:10][N:11]([C:14]2[S:15][C:16]([C:19]([O:21][CH2:22][CH3:23])=[O:20])=[CH:17][N:18]=2)[CH2:12]1)=[O:7])([CH3:4])([CH3:2])[CH3:3]
A solution of 3-tert-butoxycarbonylaminoazetidine (300 mg, 1.74 mmol), ethyl 2-bromothiazole-5-carboxylate (0.29 mL, 1.92 mmol) and diisopropylethylamine (0.61 mL, 3.48 mmol) in DMF (17 mL) was stirred at 70° C. for 10.5 hours. The reaction solution was diluted with ethyl acetate, and then the mixture was washed with brine and dried over anhydrous magnesium sulfate. Following filtration, the solvent was evaporated under reduced pressure. The resulting residue was purified by silica gel column chromatography (elution solvent: hexane/ethyl acetate=2/1) to obtain 341 mg of the title compound as a pale yellow solid (60%).
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