[C:1]1(=[O:16])[N:5]([CH2:6]/[C:7](/[CH3:10])=[CH:8]/[F:9])[C:4](=[O:11])[C:3]2=[CH:12][CH:13]=[CH:14][CH:15]=[C:2]12.[Br:17]NC(=O)CCC(N)=O>C(Cl)(Cl)(Cl)Cl>[F:9]/[CH:8]=[C:7](\[CH2:10][Br:17])/[CH2:6][N:5]1[C:4](=[O:11])[C:3]2=[CH:12][CH:13]=[CH:14][CH:15]=[C:2]2[C:1]1=[O:16]A mixture of 1-phthalimido-2-methyl-3-fluoro-2-propene (prepared in Step E) (2.09 g) and N-bromosuccinamide (1.78 g) in carbon tetrachloride (100 ml) was refluxed for 45 min. The cooled mixture is filtered and the filtrate is washed with water, dried and evaporated to leave an almost colorless oil. Chromatography (silica; 20% ether in light petroleum) followed by recrystallization of the major fractions from EtOAc/light petroleum gives:
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