[CH3:1][O:2][CH2:3][CH2:4][CH2:5][O:6][C:7]1[CH:12]=[CH:11][CH:10]=[CH:9][C:8]=1[N:13]1[C:21]2[C:16](=[CH:17][CH:18]=[CH:19][CH:20]=2)[CH:15]=[CH:14]1.ClN1C(=[O:28])CCC1=O.P(=O)(O)(O)O>C(Cl)Cl.O>[CH3:1][O:2][CH2:3][CH2:4][CH2:5][O:6][C:7]1[CH:12]=[CH:11][CH:10]=[CH:9][C:8]=1[N:13]1[C:21]2[C:16](=[CH:17][CH:18]=[CH:19][CH:20]=2)[CH2:15][C:14]1=[O:28]The compound of step 2 (3.09 g, 11.0 mmol) was dissolved in DCM (83 ml), and N-chlorosuccinimide (1.54 g, 11.6 mmol) was added. The reaction mixture was stirred at room temperature for 2 h. The solvent was removed, the resulting solid was dissolved in concentrated acetic acid (45 ml) and heated to 70° C. After the addition of phosphoric acid (9.35 ml, 137 mmol; 85%), the reaction mixture was heated to 120° C. for 2 h. The cooled mixture was diluted with water, extracted with EA, the organic layer separated, dried over sodium sulfate, filtered, and evaporated. The residue was purified by silica gel chromatography (EA/HEP 1:6). 2.38 g of the title compound was obtained.
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