[CH3:1][N:2]1[C:6]([C:7]2[CH:12]=[CH:11][N:10]=[CH:9][CH:8]=2)=[C:5]([CH:13]=[O:14])[C:4](=[O:15])[N:3]1[C:16]1[CH:21]=[CH:20][CH:19]=[CH:18][CH:17]=1.CC(=CC)C.Cl([O-])=[O:28].[Na+].OP([O-])(O)=O.[K+]>CC(O)(C)C.O>[CH3:1][N:2]1[C:6]([C:7]2[CH:8]=[CH:9][N:10]=[CH:11][CH:12]=2)=[C:5]([C:13]([OH:28])=[O:14])[C:4](=[O:15])[N:3]1[C:16]1[CH:21]=[CH:20][CH:19]=[CH:18][CH:17]=1The crude 1-methyl-3-oxo-2-phenyl-5-(pyridin-4-yl)-2,3-dihydro-1H-pyrazole-4-carbaldehyde was dissolved in t-BuOH (˜70 ml) and 2-methyl-2-butene (25 ml, 236 mmol) was added, followed by sodium chlorite (2.43 g, 27 mmol) in water (30 ml) with ˜5 ml water rinse. Then, potassium phosphate monobasic (10.35 g, 76 mmol) was added as a suspension in water (˜70 ml), and the reaction was stirred at room temperature. After 9 hours, the reaction was poured into water (400 ml) and the aqueous phase was then extracted with EtOAc, DCM, and 10:1 DCM/MeOH exhaustively until most of the product had been extracted. The organic extracts were combined, dried over sodium sulfate, filtered, and concentrated to give desired 1-methyl-3-oxo-2-phenyl-5-(pyridin-4-yl)-2,3-dihydro-1H-pyrazole-4-carboxylic acid (1.98 g, 6.7 mmol, 52% yield over two steps). MS (ESI pos. ion) m/z: 296 (MH+). Calc'd exact mass for C16H13N3O3: 295.
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