[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].C(=O)([O-])[O-].[Li+].[Li+]>O>[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 an inert atmosphere to a mixture of 117.5 g of tert.butyl 2-chloro-2,3-epoxy-3-isopropyl-butanoate and 18.5 g of lithium carbonate in 1.15 liters of hexamethylphosphonotriamide cooled to 5° C. and after the temperature was returned 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 poured into an ampoule containing a mixture of water-petroleum ether (9-1). The mixture was decanted and the aqueous phase was extracted with petroleum ether. The combined ether phases were washed with water, dried over magnesium sulfate and the petroleum ether was evaporated under reduced pressure to obtain 84.6 g of tert.-butyl 3-isopropyl-2-oxo-3-butenoate.
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