Pyridine (2.6 mL, 35.0 mmol) was added to a solution of tert-butyl-4-(2-((2S,5R)-6-(benzyloxy)-7-oxo-1,6-diaza-bicyclo[3.2.1]octane-2-carbonyl)hydrazinecarbonyl)piperidine-1-carboxylate (901 mg, 1.8 mmol) in DCM (200 mL). Then, (CF3SO2)2O (2.6 mL, 9.0 mmol) was added slowly at −10° C. The reaction mixture was stirred at rt for 3 hrs then saturated NaHCO3 was added very slowly at −10° C. The organic layer was separated and the aqueous layer was exacted with EtOAc (3×). The combined organic layer was dried over Na2SO4, and concentrated. The crude product was purified by silica gel column chromatography (2:1 EtOAc/hexanes) to give tert-butyl 4-(5-((2S,5R)-6-(benzyloxy)-7-oxo-1,6-diaza-bicyclo[3.2.1]octan-2-yl)-1,3,4-oxadiazol-2-yl)piperidine-1-carboxylate (719 mg, 82%) as a slight yellow solid. ESI-MS (EI+, m/z): 484.2 [M+H]+.
