N1C=CC=CC=1.[CH3:7][O:8][C:9](=[O:17])[CH2:10][C:11](=[O:16])[CH2:12][CH2:13][O:14][CH3:15].[Cl-].[Mg+2].[Cl-].[C:21](OC(=O)C)(=[O:23])[CH3:22]>ClCCl>[CH3:7][O:8][C:9](=[O:17])[CH:10]([C:21](=[O:23])[CH3:22])[C:11](=[O:16])[CH2:12][CH2:13][O:14][CH3:15]
Pyridine (5.3 ml, 65.92 mmol) was dropped within 3 min to an ice cooled solution of 5-methoxy-3-oxo-pentanoic acid methyl ester (5.28 g, 32.96 mmol) and anhydrous magnesium chloride (3.14 g, 32.96 mmol) in dichloromethane (50 ml). Acetic anhydride (3.27 ml, 34.6 mmol) was added within 3 min. The reaction mixture was stirred over night at RT and after partial removal of the solvent under reduced pressure it was partitioned between ether and 1 N HCl/water. The ether solution was concentrated under reduced pressure to give 5.87 g (29 mmol, 88%) 2-acetyl-5-methoxy-3-oxo-pentanoic acid methyl ester.
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