[C:1]([O:7][CH3:8])(=[O:6])[CH2:2][C:3]([CH3:5])=[O:4].[CH3:9][C:10]([CH3:12])=O.C(OC(=O)C)(=O)C>C(Cl)Cl.[Cl-].[Cl-].[Zn+2]>[C:3]([C:2](=[C:10]([CH3:12])[CH3:9])[C:1]([O:7][CH3:8])=[O:6])(=[O:4])[CH3:5]To a mixture of 9.54 g (70 mmol) of anhydrous ZnCl2, 53.9 mL (500 mmol) of methyl acetoacetate and 55 mL (750 mmol) of acetone are added 64 mL of acetic anhydride. The reaction medium is then heated for 3 days at 50° C., and then diluted with 1 L of DCM and washed with water (3×100 mL). The organic phase is dried over Na2SO4, filtered and then concentrated under reduced pressure. The residue obtained is purified by chromatography on a column of silica gel, eluting with a cyclohexane/EtOAc gradient of 0 to 10% EtOAc. After concentrating under reduced pressure, 51.5 g of methyl 2-acetyl-3-methylbut-2-enoate are obtained in the form of a colourless oil.
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