[NH2:1][C:2]1[C:7]([C:8]([O:10][CH2:11][CH3:12])=[O:9])=[CH:6][N:5]=[CH:4][N:3]=1.[C:13](OC(=O)C)(=[O:15])[CH3:14]>>[C:13]([NH:1][C:2]1[C:7]([C:8]([O:10][CH2:11][CH3:12])=[O:9])=[CH:6][N:5]=[CH:4][N:3]=1)(=[O:15])[CH3:14]Compound 21 (0.72 g, 4.3 mmol) was mixed with 8 mL of acetic anhydride and the reaction mixture was stirred under reflux for 2 h until no starting material was observed by TLC (4:1 EtOAc/hexanes). The reaction mixture was concentrated in vacuo and the product was purified by flash chromatography (CH2Cl21EtOAc) to yield 0.53 g of compound 22 in 59% yield.
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