Hydrochloric Acid → (1R*,5S*)-3-(4-bromo-2-ethylphenyl)-1-methyl-8-oxabicyclo[3.2.1]octane-2,4-dione

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(1R*,5S*)-1-Methyl-8-oxabicyclo[3.2.1]octane-2,4-dione (6 g, 38.96 mmol) and 4-dimethylaminopyridine (23.76 g, 194.75 mmol) are added to a mixture of chloroform (120 ml) and toluene (30 ml). The reaction mixture is flushed with nitrogen for 15 minutes at ambient temperature. 4-Bromo-2-ethylphenyllead triacetate (24.3 g, 42.85 mmol) is added in one portion and the reaction mixture is stirred and heated to 80° C. (pre-heated oil bath) under an atmosphere of nitrogen for 1 hour. The reaction mixture is cooled to room temperature, acidified to pH 1 with 2N aqueous hydrochloric acid, filtered through a plug of diatomaceous earth and the two phases separated. The aqueous phase is extracted with dichloromethane (2×50 ml), the organic phases are combined, washed with water, and dried over anhydrous sodium sulfate. The mixture is filtered, and the filtrate is evaporated under reduced pressure. The residue is purified by column chromatography on silica gel to give (1R*,5S*)-3-(4-bromo-2-ethylphenyl)-1-methyl-8-oxabicyclo[3.2.1]octane-2,4-dione as a white solid (6 g).

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