[NH:1]([C:8]1[C:18](=[O:19])[C:12]2[N:13]=[C:14]([CH2:16][CH3:17])[O:15][C:11]=2[C:10](=[O:20])[CH:9]=1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[Cl:21]N1C(=O)CCC1=O>C(O)(=O)C>[NH:1]([C:8]1[C:18](=[O:19])[C:12]2[N:13]=[C:14]([CH2:16][CH3:17])[O:15][C:11]=2[C:10](=[O:20])[C:9]=1[Cl:21])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1A solution of 5-anilino-2-ethyl-1,3-benzoxazole-4,7-dione (1 eq.) in acetic acid is treated with N-chlorosuccinimide (1.1 eq.) at ambient temperature. The reaction medium is maintained under stirring for 2 hours before being concentrated, followed by taking up in ethanol and concentrating again. The residue is purified by medium pressure chromatography on silica in order to produce a violet-coloured powder.
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