C([O:3][C:4]([C:6]1[CH:10]=[C:9]([C:11]2[O:12][CH:13]=[CH:14][CH:15]=2)[O:8][N:7]=1)=[O:5])C.[OH-].[Li+]>C1COCC1.CO>[O:12]1[CH:13]=[CH:14][CH:15]=[C:11]1[C:9]1[O:8][N:7]=[C:6]([C:4]([OH:5])=[O:3])[CH:10]=1To a solution of 5-furan-2-yl-isoxazole-3-carboxylic acid ethyl ester (4.14 g) in THF (130 mL) and methanol (25 mL) was slowly added 1N lithium hydroxide aqueous solution (80 mL). The resulting mixture was stirred for 15 hours, and then concentrated under reduced pressure. The remaining solution was acidified with 1N hydrochloric acid to form a solid, and the solid was filtered, washed with distilled water, dried to give 3.22 g of 5-furan-2-yl-isoxazole-3-carboxylic acid (yield: 90%) as a white solid.
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