BF3.Et2O (7.7 mL, 60.7 mmol) was added dropwise over the course of 15 minutes to a solution of 1,2,3,4,6-penta-O-acetyl-α,β-D-mannose (5d) (See FIG. 7) (4.7 g, 12.1 mmol) and Br(CH2)2OH (1.05 mL, 14.8 mmol) in CH2Cl2 (22 mL) at 0° C. under N2. After 1 hour, the solution was warmed to room temperature. After 25 hours, the reaction solution was added to ice water (20 mL) and extracted with CH2Cl2 (20 mL×2). These extracts were combined, washed with water (20 mL), sat. NaHCO3 (aq., 20 mL), water (20 mL), dried (MgSO4), filtered, and the solvent removed. The residue was crystallized from EtOAc/iso-octane to give 2-bromoethyl 2,3,4,6-tetra-O-acetyl-α-D-mannopyranoside (4i) (See FIG. 7) (3.52 g, 64%). Purification of the resulting mother liquor by flash chromatography (EtOAc:hexane, 1 :3) gave further 4i (See FIG. 7) (320 mg, 6%; 70% in total) as a white highly crystalline solid; mp 121-123° C. [lit., (Dahmén et al., “2-Bromoethyl Glycosides—Synthesis and Characterization,” Carbohydr. Res., 116:303-307 (1983), which is hereby incorporated by reference) 118-119° C. (EtOAc/iso-octane)]; [α]28D=+48.3 (c 1.31, CHCl3) [lit., (Dahmén et al., “2-Bromoethyl Glycosides—Synthesis and Characterization,” Carbohydr. Res., 116:303-307 (1983), which is hereby incorporated by reference) [α]23D=+45 (c 0.6, CDCl3)]; 1H NMR (200 MHz, CDCl3) δ 1.99, 2.05, 2.10, 2.16 (s×4, 3H×4, Ac×4), 3.52 (t, J 6 Hz, 2H, —CH2Br), 3.82-4.04 (m, 2H, —OCH2—), 4.09-4.16 (m, 1H, H-5), 4.13 (dd, J5,6 2 Hz, J6,6′ 12 Hz, 1H, H-6) 4.28 (dd, J5,6′ 6 Hz, J6,6′ 12 Hz, 1H, H-6′), 4.87 (br s, 1H, H-1), 5.22-5.40 (m, 3H, H-2, H-3, H-4). NaSSO2CH3 (230 mg, 1.72 mmol) was added to a solution of 4i (See FIG. 7) (600 mg, 1.32 mmol) in DMF (17 mL) under N2 and warmed to 55° C. After 20 hours, the solution was cooled and the solvent removed. The residue ,as purified by flash chromatography (EtOAc:hexane, 9:11) and the resulting solid recrystallized from Et2O/hexane to give 1i (See FIG. 7) (566 mg, 88%) as a white solid; mp 128-129° C. (Et2O/hexane); [α]27D=+53.2 (c 0.92, CHCl3); IR (KBr) 1739 cm−1 (C═O), 1325, 1129 cm−1 (S—SO2); 1H NMR (500 MHz, CDCl3, COSY) δ 1.97, 2.04, 2.09, 2.14 (s×4. 3H×4, Ac×4), 3.37-3.40 (m, 2H, —CH2S—), 3.38 (s, 3H, CH3SO2—), 3.79 (dt, Jd 10.5 Hz, Jt 5.8 Hz, 1H, —OCHH′—), 3.98-4.03 (m, 2H, —OCHH′—, H-5), 4.09 (dd, J5,6 2.5 Hz, J6,6′ 12.5 Hz, 1H, H-6), 4.26 (dd, J5,6′ 5.6 Hz, J6,6′ 12.5 Hz, 1H, H-6′), 4.85 (d, J1,2 0.7 Hz, 1H, H-1), 5.23-5.29 (m, 3H, H-2, H-3, H-4); 13C NMR (50 MHz, CDCl3) δ 20.6, 20.7, 20.8 (CH3COO—×4), 35.7, (—CH2S—), 50.8 (CH3SO2—), 62.5 (—OCH2—), 66.0, 66.8, 69.0, 69.2, 69.3 (C-2, C-3, C-4, C-5, C-6), 97.7 (C-1), 169.7, 169.9, 170.0, 170.6 (CH3COO—×4); HRMS m/z (FAB+): Found 487.0954 (M+H+); C17H27O12S2 requires 487.0944.
