To a suspension of zinc (123 g, 1.90 mol) in DMF (500 mL) was added TMSCl (46 mL) dropwise. The mixture was stirred at ambient temperature for 45 min. The upper clear liquid was removed and the residue was washed with DMF (200 mL×2). The resulting solid was re-suspended in DMF (200 mL) and the mixture was cooled to 0° C. A solution of (R)-methyl 2-((tert-butoxycarbonyl)amino)-3-iodopropanoate (104 g, 0.320 mol) in DMF (300 mL) was added. The mixture was stirred at 0° C. under nitrogen for 20 min. The upper clear liquid was removed and added to a solution of cyclopent-1-en-1-yl trifluoromethanesulfonate (90 g, 0.37 mol) and Pd(dppf)Cl2 (3.9 g, 4.7 mmol) in DMF (500 mL) dropwise. After addition, the reaction mixture was stirred at 50° C. under nitrogen overnight then cooled to ambient temperature. Brine (500 mL) was added and the resulting mixture was extracted with MTBE (300 mL×3). The organics were combined, washed with brine, and concentrated. The residue was purified by flash column chromatography on silica gel (petroleum ether/EtOAc=100:1 to 40:1) to afford (S)-Methyl 2-(tert-butoxycarbonylamino)-3-cyclopentenylpropanoate as viscous oil (62 g, 72% yield). 1H NMR (300 MHz, CDCl3): δ 5.48 (br s, 1H), 4.97 (d, J=6.6 Hz, 1H), 4.40-4.43 (m, 1H), 3.74 (s, 3H), 2.46-2.63 (m, 2H), 2.23-2.34 (m, 4H), 1.82-1.93 (m, 2H), 1.45 (s, 9H).
