[N:1]1[NH:2][C:3](=[O:7])[CH:4]=[CH:5][CH:6]=1.O.[C:9]1([CH3:19])[CH:14]=[CH:13][C:12](S(O)(=O)=O)=[CH:11][CH:10]=1.CO.[OH-].[Na+].[OH:24]P([O-])(O)=O.[K+]>O>[OH:24][C:12]1[CH:13]=[CH:14][C:9]([C:19]2[CH:5]([CH3:6])[CH2:4][C:3](=[O:7])[NH:2][N:1]=2)=[CH:10][CH:11]=1A 25 ml round-bottomed flask equipped with a stir bar and reflux condenser was charged with 0.10 g (0.49 mmol) of (-)-enriched-4,5-dihydro-6-(4'-hydroxyphenyl)-5-methyl-3(2H-pyridazinone (45% ee by chiral HPLC), 0.45 g (0.24 mmol) of p-toluenesulfonic acid monohydrate and methanol (15 ml). The solution was stirred under an atmosphere of nitrogen at reflux and epimerization of C-5 ° f the starting material was monitored by chiral HPLC (Cyclobond I, 75% pH 7 NaOH/KH2PO4 buffer, 25% methanol, 0.5 ml/min, lamba=280 nm). After 24 hrs, the starting material was nearly racemized. The solution was poured into water (30 ml) and extracted with EtOAc (3x35 ml). The combined EtOAc extracts were washed with saturated aqueous sodium chloride (50 ml), dried over anhydrous magnesium sulfate (5 g), filtered and concentrated in vacuo to provide 0.08 g (80%) of (±)-4,5-dihydro-6-(4'-hydroxyphenyl)-5-methyl-3(2H)-pyridazinone, m.p. 268°-273° C.; [α]D -9.8° (c 0.24, methanol); 2.5% optical purity.
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