To a solution of 3-(benzyloxycarbonylamino)-1-propanol (4.0 g, 19 mmol), as prepared in the preceding step, N-hydroxyphthalimide (3.26 g, 20 mmol) and triphenylphosphine (5.25 g, 20 mmol) in tetrahydrofuran (80 mL) was added diethyl azodicaroxylate (3.5 g, 20 mmol). The reaction mixture was stirred at room temperature overnight. Ethyl acetate (200 mL) was added, the solution washed with saturated NaHCO3 (2×100 mL) and brine (100 mL), and dried over Na2SO4. After evaporating the solvent, the residue was purified by flash column chromatography (methylene chloride to 4% ethyl acetate in methylene chloride) to give the title compound as a white solid (6.85 g, 100%). 1H-NMR (300 MHz, CDCl3) δ7.83 (m, 2H), 7.77 (m, 2H), 7.36 (m, 5H), 5.67 (br s, 1H), 5.12 (s, 2H), 4.28 (t, J=5.8 Hz, 2H), 3.51 (q, J=6.1 Hz, 2H), 1.99 (pentet, J=6.0 Hz, 2H).
