A solution of 2.20 9 cholesta-5,8-dien-3β-ol in 27 ml toluene and 6 ml cyclohexanone is refluxed for 10 minutes in a Dean-Stark apparatus. 0.57 g aluminum isopropoxide are added and the reaction mixture is refluxed for 30 minutes. After cooling and addition of sulfuric acid (2 N), the resulting mixture is extracted with ethyl acetate. The organic layer is separated, washed with saturated sodium bicarbonate solution and water, dried over anhydrous sodium sulphate and filtered. After evaporation of the solvent the residue is chromatographed with a mixture of hexane and ethyl acetate to give 1.53 g cholesta-4,8-dien-3-one as a white solid.
