Reaction Steps
Under a nitrogen atmosphere, a solution of 4 (274 mg, 0.67 mmol), n-Bu3SnCl (57 μL, 0.21 mmol, 0.3 equiv.), NaBH3CN (95% grade, 65 mg, 1.04 mmol, 1.5 equiv.), diethyl vinylphosphonate (1.1 mL, 6.91 mmol, 10 equiv.), ABCN (110 mg, 0.45 mmol, 0.67 equiv.), and tert-butanol (0.65 mL, 6.91 mmol, 10 equiv.) in diethylether (5 mL) was stirred at reflux temperature (35° C.). After 4 days, TLC (cyclohexane/EtOAc 1:1) showed complete consumption of the starting material and the formation of two new species, the desired diethyl 2-(2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl)-ethylphosphonate 5a (Rf 0.1) and side product 2,3,4,6-tetra-O-acetyl-β-D-glucopyranose 5b (Rf 0.47). The reaction was concentrated in vacuo, and the oily residue was dissolved in CH2Cl2 (30 mL). The organic solution was washed with water (3×30 mL), dried over MgSO4, and reduced to dryness. The residue was purified by chromatography on a silica gel column, which was eluted first with cyclohexane/EtOAc (1:1) and then with EtOAc/EtOH (20:1), to afford 5a as a syrup (257 mg, 71%): Rf 0.5 (EtOAc/EtOH 20:1); δH (400 MHz, CDCl3) 5.37 (dd, 1H, J5,6 3.0 Hz, J6,7 2.8 Hz, H-6), 5.24 (dd, 1H, J3,4 5.2 Hz, J4,5 9.3 Hz, H-4), 5.14 (dd, 1H, J5,6 3.3 Hz, J4,5 9.5 Hz, H-5), 4.22-4.00 (m, 7H, H-3, H-8a, H-8b, 2 OCH2CH3), 3.97 (m, 1H, H-7), 2.09, 2.04, 2.01, 1.98 (all s, 12H, 4×C(O)CH3), 2.98-1.56 (m, 4H, H-1a, H-1b, H-2a, H-2b), 1.29 (dt, 6H, 4JH,P 2.8 Hz, JH,H 7.0 Hz, 2 OCH2CH3); δC (100 MHz, CDCl3) 170.4, 170.0, 169.9, 169.8 (4×C═O), 72.9 (d, JC,P 17.0 Hz, C-3), 68.3 (C-7), 68.2 (C-4), 67.9 (C-5), 67.6 (C-6), 61.8 (d, 2JC,P 6.0 Hz, OCH2CH3), 61.7 (d, 2JC,P 5.0 Hz, OCH2CH3), 61.5 (C-8), 22.1 (C-1), 20.7 (4×C(O)CH3), 19.3 (C-2), 16.4 (d, JC,P 6.0 Hz, 2×OCH2CH3); δP (161.9 MHz, CDCl3) 32.0. m/z (ESI) 497.1772 [M+H]+, C20H33O12P requires 497.1782. 5b: Rf 0.47 (cyclohexane/EtOAc 1:1); δH (400 MHz, CDCl3) 5.35 (dd, 1H, J3,4 3.4 Hz, J6,7<1.0 Hz, H-4), 5.11 (dd, 1H, J1a,2 5.5 Hz, J1b,2 10.3 Hz, J2,3 10.3 Hz, H-2), 4.95 (dd, 1H, H-3), 4.10 (dd, 1H, J1a,1b 11.1 Hz, H-1a), 4.00 (d, 2H, J5,6 6.4 Hz, H-6a, H-6b), 3.74 (t, 1H, H-5), 3.20 (dd, 1H, H-1b), 2.06, 1.97, 1.96, 1.91 (all s, 12H, 4×C(O)CH3); δC (100 MHz, CDCl3) 170.6, 170.4, 170.3, 170.1 (4×C═O), 75.0 (C-5), 71.6 (C-3), 67.9 (C-4), 67.2 (C-1), 66.5 (C-2), 62.2 (C-6), 20.9, 20.8 (4×C(O)CH3). m/z (ESI) 350.1445 [M+NH4]+, C14H2O9 requires 350.1446.
