m-Chloroperbenzoic acid → Tert-butyl 4-{3-[4-(methylsulfonyl)benzyl]-1,2,4-oxadiazol-5-yl}piperidine-1-carboxylate

tert-Butyl 4-{3-[4(methylthio)benzyl]-1,2,4-oxadiazol-5-yl}piperidine-1-carboxylate (3.10 g, 7.96 mmol) (Method E, step 1) was dissolved in dichloromethane(100 mL), at room temperature, under argon. 3-Chloroperbenzoic acid (60% wt, 6.87 g, 23.88 mmol) was added portionwise and stirred for 1 hour. Sodium metabisulfite (1M, 250 mL) was added and stirred and the organics separated and washed with 1N sodium hydroxide and brine, dried (MgSO4) and solvents evaporated to a clear oil which crystallised upon addition of diethyl ether (50 mL). The solid was filtered, washed with a minimum of diethyl ether and dried to give tert-butyl 4-{3-[4-(methylsulfonyl)benzyl]-1,2,4-oxadiazol-5-yl}piperidine-1-carboxylate as a white fluffy solid (2.61 g, 78% yield); NMR (CDCl3): 1.46 (9H, s), 1.61 (3H, s), 1.79 (2H, m), 2.04 (2H, m), 2.93 (2H, m), 3.04 (3H, s), 4.15 (2H, s), 7.53 (2H, d), 7.90 (2H, d).