To a solution of tert-butyl 3-(3-((tert-butoxycarbonyl)(4-methoxybenzyl)amino)-2-chloro-5-cyanophenyl)-3-hydroxyazetidine-1-carboxylate (408 mg, 0.75 mmol) in dry CH2Cl2 (12 mL) at −78° C. under nitrogen was added diethylaminosulfur trifluoride (153 μL, 0.90 mmol). The mixture was allowed to warm to 0° C. over 4 h and quenched by adding 1M aqueous NaOH at −5° C. The reaction mixture was diluted with EtOAc, washed with water, brine, and dried over sodium sulfate. Solvent was removed. The residue was purified by ISCO column (12 g) chromatography, eluting with hexane containing 0 to 40% EtOAc to afford tert-butyl 3-(3-((tert-butoxycarbonyl)(4-methoxybenzyl)amino)-2-chloro-5-cyanophenyl)-3-fluoroazetidine-1-carboxylate (321 mg).
