[F:1][C:2]1[CH:7]=[CH:6][C:5]([C:8]2[O:9][C:10]([C:17]3[CH:21]=[CH:20][S:19][CH:18]=3)=[C:11](CC(O)=O)[N:12]=2)=[CH:4][CH:3]=1.C1(P(N=[N+]=[N-])(C2C=CC=CC=2)=O)C=CC=CC=1.C(N(CC)CC)C>C(O)(C)(C)C>[F:1][C:2]1[CH:3]=[CH:4][C:5]([C:8]2[O:9][C:10]([C:17]3[CH:21]=[CH:20][S:19][CH:18]=3)=[CH:11][N:12]=2)=[CH:6][CH:7]=1A mixture of 2-(4-fluorophenyl)-5-(3-thienyl)oxazol-4-yl acetic acid (1.5 g), diphenylphosphoryl azide (1.28 ml) and triethylamine (0.83 ml) in t-butanol (30 ml) was refluxed for one day. After cooling the reaction mixture, the solvent was removed under reduced pressure. Water was added to the residue and the mixture was extracted with chloroform. The organic layer was washed with a saturated aqueous sodium hydrogen carbonate solution and brine, dried over anhydrous sodium sulfate, and the solvent was removed under reduced pressure. Chloroform was added to the residue, the mixture was heated and insoluble material was removed by filtration, and the filtrate was concentrated under reduced pressure. The residue was purified by silica gel column chromatography (solvent: ethyl acetate:n-hexane=1:9→1:7) to obtain 4-(t-butoxycarbonylamino)methyl-2-(4-fluorophenyl-5-(3-thienyl)oxazole (501 mg).
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