[NH2:1][C:2]1[S:3][CH:4]=[C:5]([C:7](=[N:13][O:14][CH2:15][CH2:16][CH2:17][CH3:18])[C:8]([O:10]CC)=[O:9])[N:6]=1.CO.[OH-].[Na+]>O1CCCC1>[NH2:1][C:2]1[S:3][CH:4]=[C:5]([C:7](=[N:13][O:14][CH2:15][CH2:16][CH2:17][CH3:18])[C:8]([OH:10])=[O:9])[N:6]=1A solution of ethyl 2-(2-aminothiazol-4-yl)-2-n-butoxyiminoacetate (syn isomer, 36 g.), methanol (133 ml.), tetrahydrofuran (133 ml.) and 2N aqueous solution of sodium hydroxide (133 ml.) was stirred at 30° C. for 5 hours. After the resultant solution was concentrated in vacuo, the residue was dissolved in water. The solution was adjusted to pH 7 with 10% hydrochloric acid and treated with activated charcoal. The solution was adjusted to pH 2.0 with 10% hydrochloric acid and stirred for 20 minutes under ice cooling. The precipitates were collected by filtration, washed with water and acetone in turn, and dried to give 2-(2-aminothiazol-4-yl)-2-n-butoxyiminoacetic acid (syn isomer, 25.4 g.).
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