Br[C:2]1[CH:7]=[C:6]([Br:8])[N:5]=[C:4]([C:9]([O:11]C)=[O:10])[C:3]=1[O:13][CH2:14][C:15]1[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=1.[C:21](=O)([O-])[O-:22].[K+].[K+].CO.Cl>O>[Br:8][C:6]1[N:5]=[C:4]([C:9]([OH:11])=[O:10])[C:3]([O:13][CH2:14][C:15]2[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=2)=[C:2]([O:22][CH3:21])[CH:7]=1A vigorously stirred mixture of 15 (25.5 g), potassium carbonate (75 g) and methanol (300 mL) was heated at reflux for 30 hours. The mixture was cooled, poured into water (800 mL), and the pH adjusted to 2 by the addition of conc. HCl. The resulting mixture was extracted with CH2Cl2 (3×150 mL). The organic extracts were combined, dried (MgSO4) and the solvent was evaporated to give a nearly colorless oil (20.5 g) which slowly solidified upon standing. This was recrystallized from methanol (125 mL)/water (40 mL) to give the desired acid 16 (11.6 g), m.p. 134-135° C.
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