A solution of Ethyl (E)-4-((tertbutoxycarbonyl)amino)but-2-enoate (50 mg, 0.22 mmol, 1 equiv.) in DCM (0.5 mL, 0.4 M) was cooled to 0°C, and TFA (0.07 mL, 0.92 mmol, 4 equiv.) was added dropwise. The reaction stirred at 0°C for 10 minutes, and then allowed back to room temperature for 2 hours. Solvent was removed to give an orange oil. Product was used for the next reaction without further purification.