O[C:2]1[C:11]2[C:6](=[CH:7][CH:8]=[C:9]([N+:12]([O-:14])=[O:13])[CH:10]=2)[N:5]=[CH:4][C:3]=1[C:15]([O:17][CH2:18][CH3:19])=[O:16].C(Cl)(=O)C([Cl:23])=O.CN(C)C=O.CC(C)=O>C(Cl)(Cl)Cl>[Cl:23][C:2]1[C:11]2[C:6](=[CH:7][CH:8]=[C:9]([N+:12]([O-:14])=[O:13])[CH:10]=2)[N:5]=[CH:4][C:3]=1[C:15]([O:17][CH2:18][CH3:19])=[O:16]To a suspension of 3a in chloroform were added 4 equivalents of oxalyl chloride followed by 0.1 equiv. of dimethylformamide. The solution was refluxed for 3 hours and was quenched with 5 M sodium hydroxide solution at 4° C. The chloroform layer was collected, washed with 100 mL water and brine solution, dried over anhydrous sodium sulfate, filtered and concentrated in vacuo. Product was obtained by recrystallization using acetone. 1H-NMR (CDCl3) δ (ppm): 1.48 (3H, t, J=7.08 Hz), 4.55 (2H, q, J=7.08 Hz), 8.31 (1H, d, J=9.27 Hz), 8.62 (1H, m), 9.36 (2H, m). m/z 281.7 (MH+).
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