(S)-tert-butyl 1-(benzyl(but-3-enyl)amino)-1-oxopent-4-en-2-ylcarbamate → (S,Z)-tert-butyl 1-benzyl-2-oxo-1,2,3,4,7,8-hexahydroazocin-3-ylcarbamate

A solution of (S)-tert-butyl 1-(benzyl(but-3-enyl)amino)-1-oxopent-4-en-2-ylcarbamate (255 mg, 0.711 mmol) in ClCH2CH2Cl (120 mL) was degassed with argon for 5 min. Then, the Grubbs II catalyst (30 mg, 0.036 mmol) was added. The reaction mixture was stirred at 55-60° C. under argon for 13 hr. The reaction mixture was then cooled to rt and concentrated. The brownish residue was purified using silica gel chromatography (ISCO system) eluting with a gradient of 0-30% EtOAc/Hex to give (S,Z)-tert-butyl 1-benzyl-2-oxo-1,2,3,4,7,8-hexahydroazocin-3-ylcarbamate (110 mg, 0.333 mmol, 46.8% yield) as a colorless oil. 1H NMR (400 MHz, CDCl3) δ ppm 7.36-7.19 (m, 5H), 5.95 (d, J=6.5 Hz, 1H), 5.75-5.65 (m, 1H), 5.49-5.39 (m, 1H), 4.96 (d, J=14.8 Hz, 1H), 4.88 (q, J=6.8 Hz, 1H), 4.17 (d, J=14.9 Hz, 1H), 3.89-3.75 (m, 1H), 3.17 (dt, J=15.3, 5.8 Hz, 1H), 2.94-2.83 (m, 1H), 2.51-2.39 (m, 1H), 2.38-2.25 (m, 2H), 1.46 (s, 9H).