Reaction Steps
To a solution of crude phenyl 6-deoxy-1-thio-β-L-galactopyranoside 3 in 15 mL of pyridine is added pivaloyl chloride (4.0 mL, 3.90 g, 32.5 mmol) and DMAP (0.33 g, 2.71 mmol). The reaction mixture is heated at 100° C. for 12 h, cooled, diluted with 50 mL of CH2Cl2, washed with H2O (100 mL) and saturated NaCl (100 mL), dried over Na2SO4, filtered and concentrated to afford 3.25 g of phenyl 6-deoxy-2,3,4-tri-O-pivaloyl-1-thio-β-L-galactopyranoside 4 as a brown oil. This oil is purified by flash chromatography (15% EtOAc/petroleum ether) to afford 0.53 g (48%) of the pure compound. An additional 0.81 g of a brown oil, which that appeared to be a mixture of incompletely acylated products, is also isolated. This material is resubjected to the reaction conditions for 48 h and provided an additional 0.21 g (19%, total yield 67% for 2 steps): Rf 0.48 (15% EtOAc/petroleum ether); 1H NMR (CDCl3, 270 MHz) δ 7.50-7.59 (m, 2H), 7.23-7.35 (m, 3H), 5.16-5.30 (m, 2H), 5.08 (dd, J=9.9, 3.0 Hz, 1H, H-3), 4.66 (d, J=9.6 Hz, 1H, H-1), 3.90 (q, J=6.3 Hz, 1H, H-5), 1.21 (s, 9H), 1.18 (s, 9H), 1.21 (s, 9H), 1.21 (d, J=6.6 Hz, 3H, H-6); 13C NMR (CDCl3, 68 MHz) δ 177.2, 177.4, 177.1, 133.5, 131.1, 128.6, 128.4, 128.1, 127.7, 85.1, 73.3, 72.6, 69.9, 66.3, 38.9, 38.6, 26.9, 27.0, 16.4; FABMS C27H39O7S (MNa+) calcd 531.2392, found 531.2404.
