A mixture of 7.8 g of crude 1-(3,4-difluorophenyl)-4-(1,4-dioxa-8-spiro[4.5]decyl) cyclohexanol, 1.05 ml of ethylene glycol, 1.05 g of Amberlyst® 15 (strongly acid ion exchange resin, Fluka AG) and 80 ml of ethylene chloride was refluxed through neutral aluminum oxide for 3 hours. Subsequently, the mixture was cooled to room temperature and washed twice with water. The aqueous phases were extracted twice with methylene chloride. The organic phases where dried over sodium sulfate, filtered and concentrated. Chromatographic purification of the residue on silica gel with hexane/ethyl acetate (vol. 96:4) gave 4,9 g of 8-[4-(3,4-difluorophenyl)-3-cyclohexenyl]-1,4-dioxaspiro [4.5]decane as colorless crystals.
