2.0 g of 4-(cis-3-allyloxycyclohexyloxymethyl)-2-(4-fluorophenyl)-5-methyl-oxazole are dissolved in 50 ml of diethyl ether, and 3.8 g of sodium periodate, dissolved in 50 ml of water, are added. At 0° C., 1 ml of an osmium tetroxide solution (2.5% by weight in tert-butanol) is added, and the mixture is stirred vigorously at room temperature. After 8 hours, 100 ml of methyl tert-butyl ether are added, and the mixture is washed with a saturated sodium thiosulfate solution. The organic phase is dried over magnesium sulfate and the solvent is removed under reduced pressure. The residue is purified on silica gel (n-heptane:ethyl acetate=1:1→1:5). This gives 1.4 g of [cis-3-[2-(4-fluorophenyl)-5-methyloxazol-4-ylmethoxy]cyclohexyl]acetaldehyde as a colorless oil. C20H25NO4 (343.42), MS (ESI): 344 (M+H+), Rf(n-heptane:ethylacetate=1:1)=0.25.
