[CH3:1][N:2]1[C:10]2[C:5](=[CH:6][CH:7]=[CH:8][CH:9]=2)[C:4]([CH:11]=[CH2:12])=[N:3]1.[N+](=[CH:15][C:16]([O:18][CH2:19][CH3:20])=[O:17])=[N-]>C1(C)C=CC=CC=1>[CH3:1][N:2]1[C:10]2[C:5](=[CH:6][CH:7]=[CH:8][CH:9]=2)[C:4]([CH:11]2[CH2:12][CH:15]2[C:16]([O:18][CH2:19][CH3:20])=[O:17])=[N:3]1A solution of compound 2 (1.1 g, 7 mmol) in toluene (5 mL) was treated with ethyl diazoacetate (1.2 g, 10 mmol) and stirred at reflux overnight under N2. The mixture was concentrated and the residue was purified by gradient elution on silica gel (PE: EA=5:1) to afford the title compound as a pale yellow oil.
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