P(Cl)(Cl)([Cl:3])=O.O=[C:7]1[NH:12][N:11]=[C:10]([C:13]([O:15][CH2:16][CH2:17][CH2:18][CH3:19])=[O:14])[CH:9]=[CH:8]1>C(#N)C.O>[Cl:3][C:7]1[N:12]=[N:11][C:10]([C:13]([O:15][CH2:16][CH2:17][CH2:18][CH3:19])=[O:14])=[CH:9][CH:8]=1To a mixture of phosphorus oxychloride (20 ml) and acetonitrile (40 ml) heated at reflux was added a solution of n-butyl 6-oxo-1,6-dihydropyridazine-3-carboxylate (20 g) in acetonitrile (80 ml). The reaction was heated at reflux for 30 minutes, cooled and added to an ice cooled solution of K2C03 (87.8 g) in water (600 ml) with vigorous stirring. The product was filtered off, washed with water and dried at 60° C. to give n-butyl 6-chloropyridazine-3-carboxylate (17.5 g, 80% yield), mpt 110-111° C.
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