[CH3:1][O:2][C:3](=[O:11])[CH2:4][C:5](=[O:10])[CH2:6][CH2:7][O:8][CH3:9].[Cl-].[Mg+2].[Cl-].N1C=CC=CC=1.[C:21](OC(=O)C)(=[O:23])[CH3:22]>ClCCl>[CH3:1][O:2][C:3](=[O:11])[CH:4]([C:21](=[O:23])[CH3:22])[C:5](=[O:10])[CH2:6][CH2:7][O:8][CH3:9]To an ice cooled solution of 5.28 g (32.96 mmol) 5-methoxy-3-oxo-pentanoic acid methyl ester and 3.14 g (32.96 mmol) anhydrous magnesium chloride in 50 ml dichloromethane was dropped within 3 min 5.3 ml (65.92 mmol) pyridine. 3.27 ml (34.61 mmol) of acetic anhydride was then added within 3 min. The reaction mixture was stirred over night at RT and after concentration under reduced pressure it was partitioned between ether, 1N HCl and water. The ether solution was concentrated under reduced pressure to give 5.87 g pure 2-acetyl-5-methoxy-3-oxo-pentanoic acid methyl ester.
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