C([O:3][C:4]([C:6]1[C:11]([CH3:12])=[C:10]([C:13]#[N:14])[C:9](=[O:15])[N:8]([C:16]2[CH:21]=[CH:20][C:19]([O:22][CH3:23])=[CH:18][CH:17]=2)[N:7]=1)=[O:5])C.[OH-].[Na+]>C(O)C.O>[C:13]([C:10]1[C:9](=[O:15])[N:8]([C:16]2[CH:21]=[CH:20][C:19]([O:22][CH3:23])=[CH:18][CH:17]=2)[N:7]=[C:6]([C:4]([OH:5])=[O:3])[C:11]=1[CH3:12])#[N:14]To a solution of 5-cyano-4-methyl-1-(4-methoxy-phenyl)-6-oxo-1,6-dihydro-pyridazine-3-carboxylic acid ethyl ester (15 g, 0.048 mol, prepared as described in example 23) in a mixture of ethanol (250 ml) and water (100 ml) was added sodium hydroxide (2.1 g, 0.053 mol). The reaction mixture was stirred at room temperature for 16 h, the volatiles were evaporated and the residue diluted with water (200 ml). The aqueous phase was washed with ethyl acetate (250 ml) and pH was adjusted to pH=2 by addition of concentrated hydrochloric acid. The precipitate was filtered off and washed with water (2×80 ml) and dried in vacuo at 50° C. for 16 h which afforded 12.3 g (90%) of 5-cyano-1-(4-methoxy-phenyl)-4-methyl-6-oxo-1,6-dihydro-pyridazine-3-carboxylic acid as a solid.
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