C([Li])(CC)C.[F:6][C:7]1[CH:12]=[CH:11][C:10]([F:13])=[CH:9][CH:8]=1.[N:14]1[CH:19]=[C:18]2[C:20]([O:22][C:23](=[O:24])[C:17]2=[CH:16][N:15]=1)=[O:21].[Cl-].[NH4+]>O1CCCC1>[F:6][C:7]1[CH:12]=[CH:11][C:10]([F:13])=[CH:9][C:8]=1[C:20]([C:18]1[C:17]([C:23]([OH:24])=[O:22])=[CH:16][N:15]=[N:14][CH:19]=1)=[O:21]Sec-butyllithium (1.32 M in cyclohexane; 1.25 mL) is added dropwise via syringe over 0.25 h to a stirred solution of 1,4-difluorobenzene (0.162 g) in tetrahydrofuran (THF) (5 mL) at -84° C. under a nitrogen atmosphere. The yellow mixture is stirred for an additional 45 min at -80° C. and then added via a canula over 5 min to a stirred solution of pyridazine 4,5-dicarboxylic acid anhydride (0.22 g; prepared according to J.Het Chem. 14, 1099, (1977)) in THF at -80° C. by nitrogen pressure. The mixture is warmed to room temperature overnight and neutralized with amonium chloride. After removal of THF at reduced pressure the resultant tan solid is treated with an aqueous sodium bicarbonate solution (10 mL) and washed with diethyl ether (10 mL). The aqueous phase is acidified with aqueous hydrochloric acid. The precipitate is collected by filtration, washed with cold water (3×10 mL) and dried to give 4-(2',5'-difluorobenzoyl)pyridazine-5-carboxylic acid (0.23 g) as an off-white solid, m.p. 202°-205° C.
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