[CH2:1](I)[CH2:2][CH2:3][CH3:4].[OH:6][N:7]=[C:8]([C:14](=[O:16])[CH3:15])[C:9]([O:11][CH2:12][CH3:13])=[O:10].C(=O)([O-])[O-].[K+].[K+]>CC(C)=O>[CH2:1]([O:6][N:7]=[C:8]([C:14](=[O:16])[CH3:15])[C:9]([O:11][CH2:12][CH3:13])=[O:10])[CH2:2][CH2:3][CH3:4]n-Butyl iodide (46.9 g.) was added dropwise to a stirred suspension of ethyl 2-hydroxyimino-3-oxobutyrate (syn isomer, 40 g.), potassium carbonate (52.7 g.) and acetone (200 ml.) under ice-cooling over 5 minutes, and stirred at room temperature for 4 hours. The resultant solution was filtered, and washed with acetone. The filtrate and washing solution were combined together and concentrated in vacuo. After adding water (300 ml.) to the residue, the solution was extracted with methylene chloride three times. The solution was washed with a saturated aqueous solution of sodium chloride, dried over magnesium sulfate and concentrated in vacuo to give ethyl 2-n-butoxyimino-3-oxobutyrate (syn isomer, 48.8 g.), oil.
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