CC(C)([O-])C.[K+].[CH3:7][O:8][C:9](=[O:17])[C:10]1[CH:15]=[CH:14][C:13]([OH:16])=[CH:12][CH:11]=1.[Cl:18][C:19]1[N:20]=[N:21][C:22](Cl)=[CH:23][CH:24]=1>C1COCC1.O>[CH3:7][O:8][C:9](=[O:17])[C:10]1[CH:15]=[CH:14][C:13]([O:16][C:22]2[N:21]=[N:20][C:19]([Cl:18])=[CH:24][CH:23]=2)=[CH:12][CH:11]=1Potassium tert-butoxide (0.87 g, 7.75 mmol) was added in portions to a solution of 4-hydroxybenzoic acid methyl ester 1 (1.15 g, 7.56 mmol) in anhydrous THF (25 ml). The mixture was stirred at room temperature for 30 minutes, then 3,6-dichloro-pyridazine (1.12 g, 7.56 mmol) was added. The reaction mixture was stirred at room temperature for 1 h and heated at reflux for 14 h. The mixture was cooled to room temperature and diluted with water (100 ml). The formed precipitate was collected by filtration, washed with water and dried to obtain 1.315 g (66%) of 4-(6-chloro-pyridazin-3-yloxy)-benzoic acid methyl ester which was used for the next step without further purification.
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