Water → 1-Vinyl-4-ethyl-2,6,7-trioxabicyclo[2,2,2] octane

25 g (0.1 moles) of the product obtained in step (b) above was added dropwise over about one hour at room temperature to a solution of 11 g (0.1 moles) of potassium t-butoxide in 100 ml of tetrahydrofuran placed in a 250 ml flask. The mixture was heated at reflux temperature for 5 hours and the reaction solution obtained was poured into water. The resulting solution was extracted with ethyl ether and the organic layer was dried over anhydrous magnesium sulfate and concentrated by evaporation of the ether. The residue was distilled under reduced pressure to give 14 g (83%) of the title compound with a boiling point of 68°-72° C./2 mmHg and a specific gravity of 1.216 (Method D).