Suspend diethyl-(1S,2S,5R,6R)-2-amino-4-oxo-bicyclo[3.1.0]hexane-2,6-dicarboxylate-hydrochloride (55.0 g, 188.5 mmol) in tetrahydrofuran (220 mL), then add water (220 mL) and potassium carbonate (92.1 g, 659.9 mmol). Stir the resulting mixture for 30 minutes. Add benzyl chloroformate (26.7 mL, 175.3 mmol) to the mixture over 45 minutes, keeping the reaction temperature below 25° C. Stir reaction mixture for 30 minutes, then dilute with ethyl acetate (550 mL) and water (275 mL). Separate the phases and back extract the aqueous layer with ethyl acetate (250 mL). Combine the organics and wash it sequentially with aqueous HCl (0.5N, 100 mL), saturated NaHCO3 (100 mL) and brine (100 mL). Dry the organic solution over Na2SO4, filter and concentrate in vacuo to afford the title compound as a clear oil (67.6 g, 92.1%). 1H NMR (CDCl3) δ 1.24-1.26 (m, 6H), 2.36 (bs, 1H), 2.47 (dd, 1H), 2.78 (dd, 1H), 2.90 (dd, 1H), 4.09-4.19 (m, 4H), 5.08 (s, 2H), 5.73 (s, 1H), 7.24-7.36 (m, 5H).
