Reaction Steps
To a solution of (S)-methyl 3-((2S,3R)-2,3-bis(benzyloxy)-4-oxobutoxy)-2-((tert-butoxycarbonyl)amino)propanoate (7.55 g, 15.05 mmol) in DCM (30 ml) and THF (30 ml) at −78° C. was added triisopropoxy(methyl)titanium, 1.0 M in THF (31.6 ml, 31.6 mmol) and the reaction was stirred at −78° C. for 2 h, warmed to −20° C., and stored at −20° C. overnight. The reaction was warmed to 0° C., stirred for 4 h between 0° C. and −10° C., and then quenched at this temperature with saturated aqueous NH4Cl. The reaction mixture was extracted with EtOAc, and the combined extracts were washed with brine, dried over MgSO4, filtered, and concentrated. The crude residue was purified by flash chromatography (SiO2, hexanes/EtOAc) to yield the title compound as a colorless oil (4.59 g, 59%, diastereomer selectivity=6:1): 1H NMR (400 MHz, CDCl3) δ 7.45-7.14 (m, 11H), 5.45 (d, J=8.8 Hz, 1H), 4.67 (d, J=11.6 Hz, 1H), 4.61-4.51 (m, 3H), 4.50-4.41 (m, 1H), 3.90 (dd, J=9.4, 3.0 Hz, 1H), 3.84-3.78 (m, 1H), 3.74-3.61 (m, 6H), 3.31 (dd, J=6.8, 4.0 Hz, 1H), 2.85 (d, J=4.5 Hz, 1H), 1.45 (s, 9H), 1.20 (d, J=6.2 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ 171.04, 155.45, 137.99, 137.76, 128.51, 128.44, 128.12, 128.00, 127.97, 127.87, 81.43, 80.05, 77.91, 73.55, 72.88, 71.60, 70.91, 67.53, 54.00, 52.47, 28.34, 19.89; ESIMS m/z 540.6 ([M+Na]+).
