Reaction Steps
A mixture of 3-O-allyl-2,4,6-tri-O-benzoyl-α-D-mannopyranosyl trichloroacetimidate [26] (902 mg, 1.21 mmol) and benzyl 3,4,6-tri-O-benzyl-α-D-mannopyranoside [27] (723 mg, 1.34 mmol) in 1,2-DCE (10 mL), was stirred in the presence of mol. sieves (1.0 g of 3 Å powder) under an atmosphere of argon (30 min). The mixture was cooled (0° C.) with continued stirring (10 min) prior to the addition of TMSOTf (219 μL, 1.21 mmol). After some time (10 min), Et3N (100 μL) was introduced and the mixture was filtered. The solvent was evaporated and the residue subjected to FC (10-50% EtOAc/hexane) to yield the tribenzoate (24) as, a colourless oil (1.14 g, 84%). 1H NMR (CDCl3) δ 3.67-3.81, 3.88-3.95, 4.06-4.15, 4.30-4.35 (4 m, 12H; H-2I,-3I,-4I,-5I,-6aI,-6bI,-3II,-5II,-6aII,-6bII, OCH2), 4.94-4.70 (m, 7H; CH2Ph), 4.84 (d, 1H, JA,B 10.8 Hz; A of AB quartet), 4.93-4.96, 5.04-5.09 (2 m, 2H; ═CH2), 5.02 (d, 1H, J1,2 1.9 Hz; H-1I), 5.24 (d, 1H; J1,2 1.9 Ha; H-1II), 5.59-5.69 (m, 1H; ═CH), 5.72 (dd, 1H, J2,3 3.1 Hz; H-2II), 5.75 (dd, 1H, J3,4 9.8, J4,5 9.9 Hz; H-4II), 7.09-7.58, 7.97-8.06 (2 m, 35H; Ar). 13C NMR (CDCl3) δ 61.50, 63.49 (2 C; C-6I,-6II), 68.63, 69.17, 69.31, 69.46, 69.64, 71.08, 72.04, 72.64, 73.60, 74.73, 75.30, 75.38 (13 C; C-3I,-4I,-5I,-2II,-3II,-4II,-5II, OCH2, CH2Ph), 79.97 (C-2I), 98.52, 99.60 (C-1I,-1II), 117.67 (═CH2), 127.70-138.43 (43 C; ═CH, Ar), 165.61, 165.69, 166.42 (3 C; C═O).
