Reaction Steps
Under an atmosphere of N2, a 2.0M solution of Me3Al in toluene (PhMe) (Aldrich, 150 ml, 300 mmol) was added dropwise to a stirred and ice-cooled suspension of NH4Cl (14.9 g, 278 mmol) in dry PhMe (280 ml). The stirring at room temperature for 30 minutes gave rise to the clear and homogeneous reaction mixture. To this was added a solution of (2R*,3S*,4S*,5S*)-1-benzyloxycarbonyl-4-benzyloxymethyl-5-(t-butyldimethylsilyloxy)methyl-3-methoxycarbonyl-2-phenylpyrrolidine (16.8 g, 27.8 mmol) in dry PhMe (30 ml) dropwise. The resultant turbid reaction mixture was stirred and heated at an inner temperature of 50 C. for 24 hours. H2O (20 ml) was added cautiously to the ice-cooled and stirred reaction mixture. To this was then added a 1.0M potassium sodium tartrate aqueous solution (280 ml, 280 mmol), and the stirring was continued under the same cooling conditions for an hour. The mixture was filtered through a pad of Celite, and the filter cake was washed with AcOEt throughly. From the combined filtrate and AcOEt washings the organic layer was separated, and the aqueous layer was extracted with AcOEt (100 ml×3). The combined organic layer and AcOEt extracts were washed with sat. NaCl aq. solution (×1), dried (MgSO4), and concentrated in vacuo to give a foam (15.4 g). This was chromatographed over SiO2 (Merck Kieselgel 60, 160 g). Elution with n-hexane-AcOEt (6:1→4:1→1:1) gave pure title compound (12.0 g, 73%) as a white glass: IRmax (film): 3350(m), 3200(m), 1699(vs), 1680(vs), 1605(m), 1490(m), 1100(s), 780(s), 730(s), 697(s) cm-1 ; 1H-NMR δ: 7.53-7.40(m, 3H), 7.40-7.03(m, 12H), 5.60(br.s, 1H), 5.27(d, J=9.2 Hz, 1H), 5.03(br.s, 2H), 4.48(br.s, 2H), 4.47(dd, J=10.3, 8.1 Hz, 1H), 4.27(br.s, 1H), 3.99(dd, J=10.3, 2.9 Hz, 1H), 3.88-3.76(m, 1H), 3.70(dd, J=10.3, 3.3 Hz, 1H), 3.60(dd, J=10.3, 4.7 Hz, 1H), 3.32(dd, J=11.7, 9.2 Hz, 1H), 3.24-3.08(m, 1H), 0.90(br.s, 9H), 0.05(br.s, 6H) ppm.
