[Br-].[Li+].Cl[C:4]1([O:17][C:12]1([CH:14]([CH3:16])[CH3:15])[CH3:13])[C:5]([O:7][C:8]([CH3:11])([CH3:10])[CH3:9])=[O:6].O>C(=O)([O-])[O-].[Li+].[Li+]>[CH:14]([C:12](=[CH2:13])[C:4](=[O:17])[C:5]([O:7][C:8]([CH3:11])([CH3:10])[CH3:9])=[O:6])([CH3:16])[CH3:15]118 g of anhydrous lithium bromide were added under a nitrogen atmosphere at 5° C to a mixture of 117.5 g of tert.-butyl 2-chloro-2,3-epoxy-3-isopropyl-butanoate in 18.5 g of lithium carbonate and 1.15 liters of hexamethylphosphortriamide and after returning to room temperature, the mixture was stirred under a nitrogen atmosphere for 48 hours. 500 ml of distilled water were added thereto and the mixture was added to a decanting flask containing a 9:1 mixture of water and petroleum ether. After decanting, the aqueous phase was extracted with petroleum ether and the combined organic phases were washed with water, dried over magnesium sulfate, then the petroleum ether was evaporated under reduced pressure to obtain 84.6 g of tert.-butyl 3-isopropyl-2-oxo-3-butenoate in the form of a yellow liquid soluble in the usual organic solvents and insoluble in water.
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