C(O[C:4]1[O:8][C:7]([CH2:9][CH2:10][C:11]([O:13][CH3:14])=[O:12])=[N:6][CH:5]=1)C.[C:15]1(=O)[O:20][C:18](=[O:19])[CH:17]=C1.C[Si](C=[N+]=[N-])(C)C.[CH2:29]([O:31][CH2:32][CH3:33])C.Cl.C[OH:36]>>[OH:8][C:4]1[C:17]([C:18]([O:20][CH3:15])=[O:19])=[C:33]([C:32]([O:31][CH3:29])=[O:36])[C:7]([CH2:9][CH2:10][C:11]([O:13][CH3:14])=[O:12])=[N:6][CH:5]=1A mixture of methyl 3-(5-ethoxy-1,3-oxazol-2-yl)propanoate (7.00 g, 35.1 mmol) and maleic anhydride (3.44 g, 35.1 mmol) was stirred at room temperature for 2 hr, 10% hydrochloric acid-methanol solution (100 mL) was added, and the mixture was heated under reflux for 15 hr. The solvent was evaporated under reduced pressure, and the residue was purified by silica gel column chromatography (ethyl acetate/methanol=100/0→70/30). The purified product was dissolved in methanol, 2M trimethylsilyldiazomethane/diethyl ether solution (34 mL, 68 mmol) was added at room temperature, and the mixture was stirred for 30 min. The solvent was evaporated under reduced pressure, and the residue was purified by silica gel column chromatography (ethyl acetate/hexane=25/75→50/50) to give the title compound (3.10 g, yield 30%).
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