A mixture of 10.8 g (31.5 mmol) of the vinylsulphone product of step 3 of Example 17 and 24 g (165 mmol) of the 3-trimethylsiloxy-1,3-butadiene in 100 mL of trifluorotoluene in a sealed tube was heated at 150° C. for 15 h. It was concentrated, the residue was dissolved in 50 mL of THF. To this solution was added 3 mL of 1N HCl, the mixture was stirred at room temperature for 30 min. It was diluted with 300 mL of methylene chloride, washed with 50 mL of brine, and concentrated. The residue was recrystallized from ethyl acetate to give 6.8 g of the ketone. Chromatography of the mother liquid gave additional 3.4 g of the ketone.
