To a suspension of 4-(5-cyano-benzooxazol-2-ylamino)-piperidine-1-carboxylic acid tert-butyl ester (1.03 g, 3.01 mmol, 1.0 equiv; intermediate T (2-(piperidin-4-ylamino)-benzooxazole-5-carbonitrile)/step 1) and 0.084 g (0.6 mmol) of potassium carbonate in DMSO (5 mL) was added a solution of 35% hydrogen peroxide in water (0.53 mL, 0.59 g, 6.02 mmol, 2.0 equiv) and the reaction mixture stirred at ambient temperature for 24 h. The solution was poured on crashed ice, the reaction mixture extracted with dichloromethane/2-propanol (4:1, 3×50 mL) and the combined organic phases dried over MgSO4. The organic solvent was evaporated under reduced pressure and the crude reaction product purified with column chromatography on silica eluting with a gradient of dichloromethane/methanol (100:0→95:5) containing 33% of NH4OH to yield 1.05 g (97%) of the title compound. MS (ESI): 361.2 [M+H]+.
