50 mg of 3-{4-[4-hydroxymethyl-2-(4-trifluoromethyl-phenyl)-thiazol-5-ylmethoxy]-2-methoxy-phenyl}-4H-[1,2,4]oxadiazol-5-one were dissolved in 2 mL of dimethylformamide by heating to 60° C. and 2 mL of dichloromethane was added. To the resulting solution was added 90 mg of manganese dioxide. The reaction mixture was heated to 60° C. overnight. 5 mL of dimethylformamide was added. The hot mixture was filtered through celite and washed with dichloromethane/methanol. The filtrate was concentrated under reduced pressure to give 30 mg of 5-[3-methoxy-4-(5-oxo-4,5-dihydro-[1,2,4]oxadiazol-3-yl)-phenoxymethyl]-2-(4-trifluoromethyl-phenyl)-thiazole-4-carbaldehyde which was used in the next step without further purification.
