C[O:2][C:3]([C:5]1[C:6]([C:12]2[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=2)=[N:7][O:8][C:9]=1[CH2:10][CH3:11])=[O:4].O[Li].O>C1COCC1.O>[CH2:10]([C:9]1[O:8][N:7]=[C:6]([C:12]2[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=2)[C:5]=1[C:3]([OH:4])=[O:2])[CH3:11]8.0 g (34 mmol) of 5-Ethyl-3-phenyl-isoxazole-4-carboxylic acid methyl ester (prepared according to: Synthesis 2003; 1347-1356) was dissolved in 50 mL of THF, to which 7.2 g (170 mmol) LiOH.H2O in 25 ml of H2O was added in one portion. The reaction mixture was refluxed for 12 h. After evaporation of THF, the aqueous solution was acidified with 2N HCl to pH=2. After extraction with ethyl acetate (3×100 mL), the combined organic extracts were dried over Na2SO4 and evaporated to dryness to give 5-Ethyl-3-phenyl-isoxazole-4-carboxylic acid (6.32 g) in 72.3% yield as a red solid. (m/e): 216.2 (M−; 100%).
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