Acetic Anhydride → 3,5-Dioxohexanoic acid

To a solution of 1.28 g of 1-(2,4-dihydroxy-2,6,6-trimethylcyclohexyl)hex-1-en-3-ol in 50 ml of triethylamine was slowly added 1.2 ml of acetic anhydride under ice-cooling. To the mixture was further added 120 mg of p-dimethylaminopyridine. The mixture was allowed to stand at room temperature overnight. The reaction mixture was poured onto ice and extracted with diethyl ether. The extract was washed successively with a 0.5N hydrochloric acid aqueous solution and a saturated sodium chloride aqueous solution and dried over anhydrous magnesium sulfate, followed by filtration. The filtrate was concentrated under reduced pressure to obtain 1.25 g of a triacetate compound as an oily product. The resulting triacetate compound (1.21 g) was dissolved in 130 ml of carbon tetrachloride, followd by cooling to -5° C. to 0° C. with ice-cold sodium chloride. To the solution was slowly added dropwise 8.3 ml of bromine. After completion of the addition, the mixture was allowed to stand at 0° C. for 1 hour, washed successively with a 10% aqueous solution of sodium hydrogen carbonate and a saturated sodium chloride aqueous solution, and dried over ahhydrous magnesium sulfate. After filtration, the filtrate was concetrated under reduced pressure to obtain 1.95 g of an oily product.