[CH3:1][O:2][C:3](=[O:19])[CH2:4][CH:5]([NH:9][C:10]([C:12]1[CH:13]=[N:14][C:15]([Cl:18])=[CH:16][CH:17]=1)=[O:11])[C:6](=O)[CH3:7].S(=O)(=O)(O)O>C(OC(=O)C)(=O)C>[CH3:1][O:2][C:3](=[O:19])[CH2:4][C:5]1[N:9]=[C:10]([C:12]2[CH:13]=[N:14][C:15]([Cl:18])=[CH:16][CH:17]=2)[O:11][C:6]=1[CH3:7]3-[(6-Chloro-pyridine-3-carbonyl)-amino]-4-oxo-pentanoic acid methyl ester is dissolved in acetic anhydride (75 mL) and concentrated sulfuric acid is added in 500 uL portions five times over a four hour period. The reaction is monitored by HPLC. The reaction is then heated to 40° C. until the starting material is consumed. The reaction is allowed to proceed at room temperature overnight. The reaction is then concentrated to dryness and purified by column chromatography. This procedure yielded (12.8 g, 48 mmol) 22% of the desired oxazole over four steps.
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