Reaction Steps
To a solution of (S)-methyl 3-((2S,3R)-2,3-bis(benzyloxy)-4-oxobutoxy)-2-((tert-butoxycarbonyl)amino)propanoate (0.980 g, 1.95 mmol) in DCM (18.61 ml) at −78° C. was added a 3.0 M solution of methylmagnesium bromide in diethyl ether (Et2O) (1.30 ml, 3.91 mmol) and the reaction was stirred at −70° C. for 1 h, warmed slowly to −20° C. over 2 h, and then quenched at −20° C. with H2O. The organic layer was separated and the aqueous layer was extracted with EtOAc. The combined organic phases were washed with brine, dried over MgSO4, filtered, and the filtrate was concentrated and purified by flash chromatography (SiO2, hexanes/EtOAc gradient) to yield the title compound as a colorless oil (0.475 g, 47%): 1H NMR (400 MHz, CDCl3) δ 7.37-7.27 (m, 10H), 5.43 (d, J=8.6 Hz, 1H), 4.71 (d, J=14.0 Hz, 1H), 4.69 (d, J=14.4 Hz, 1H), 4.55 (dd, J=11.5, 2.6 Hz, 2H), 4.49-4.41 (m, 1H), 3.96-3.84 (m, 2H), 3.75 (dd, J=10.1, 5.0 Hz, 1H), 3.72 (s, 3H), 3.71-3.63 (m, 3H), 3.32-3.29 (m, 1H), 2.26 (d, J=6.3 Hz, 1H), 1.45 (s, 9H), 1.14 (d, J=6.4 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ 171.20, 155.58, 138.36, 138.21, 128.59, 128.53, 128.21, 128.07, 128.05, 127.89, 82.88, 80.16, 78.55, 74.94, 73.18, 71.71, 71.34, 67.04, 54.16, 52.58, 28.46, 20.30; ESIMS m/z 516.3 ([M−H]−).
