Aluminum amalgam was prepared from aluminum foil (1.16 g, 14.4 mmol) and mercuric chloride (12 mg, catalytic amount) in 20 mL of anhydrous THF by vigorously stirring the mixture at room temperature for 1 hour under an argon atmosphere. A solution of propargyl bromide (4.80 mL, 80 wt. % in toluene, 43.1 mmol) in 25 mL of anhydrous THF was slowly added to a stirred suspension maintaining a temperature of 30° C.-40° C., and after addition, stirring at 40° C. was continued until a dark gray solution was obtained (ca. 1 hour). The propargyl aluminum sesquibromide solution was added to a solution of 4-(3-[1,3]dioxan-2-ylphenyl)-1,1,1-trifluoro-4-methylpentan-2-one (5.6 g, 14.2 mmol) in 100 mL of anhydrous diethyl ether at −78° C. The reaction mixture was stirred at this temperature for 3 hours, and then was allowed to warm to room temperature, at which time it was stirred for 12 hours. The reaction mixture was then poured into 20 mL of ice-water and extracted with four 30 mL portions of diethyl ether. The combined extracts were washed with 20 mL of brine, dried over magnesium sulfate, and concentrated in vacuo. Chromatography on silica gel (100% hexanes to 40% ethyl acetate in hexanes, gradient) afforded 2.5 g of the title compound as an oil (50% yield).
