P(Cl)(Cl)(Cl)=O.[Br:6][CH2:7][CH2:8][CH2:9][CH2:10][N:11]1[C:19]2[C:14](=[N:15][C:16]([O:20][CH3:21])=[CH:17][CH:18]=2)[CH:13]=[CH:12]1.CN(C)[CH:24]=[O:25]>>[Br:6][CH2:7][CH2:8][CH2:9][CH2:10][N:11]1[C:19]2[C:14](=[N:15][C:16]([O:20][CH3:21])=[CH:17][CH:18]=2)[C:13]([CH:24]=[O:25])=[CH:12]1Under argon and in an anhydrous medium, 730 μl (7.95 mmol) of phosphorus oxychloride are added dropwise to 12.5 ml of N,N-dimethylformamide maintained at 0° C.: after 30 minutes' stirring, 1.50 g (5.3 mmol) of the compound obtained in Step A dissolved in 25 ml of N,N-dimethylformamide are added by transfer. The reaction mixture is stirred for 30 minutes at 0° C. and then for 3 hours at room temperature. The reaction mixture is evaporated to dryness and then taken up in water, the aqueous phase is rendered alkaline with a 6N sodium hydroxide solution and extracted several times with ethyl acetate. The combined organic phases are dried over magnesium sulphate, filtered and then evaporated. After washing with a petroleum ether/diethyl ether mixture, the title compound is obtained in the form of a yellow oil.
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