To a mixture of D-mannose pentaacetate (16.0 g, 0.041 mol) and p-thiocresol (7.6 g, 0.0615 mol) in CH2Cl2 (200 mL), boron trifluoride diethyl etherate (6.8 mL, 0.0533 mol) was added. The mixture was stirred overnight. The reaction mixture was then diluted with CH2Cl2 (200 mL), washed with sat. NaHCO3 (2×120 mL) and water (100 mL). The organic layer was dried over Na2SO4. The solvent was removed, and the residue was purified by column chromotography on silia gel (hexanes/EtOAc 3:1) to give product (16.2 g, 87%) as a syrup: 1HNMR (500 MHz, CDCl3), δ 7.38 (d, J=8.0 Hz, 2H), 7.12 (d, J=8.0 Hz, 2H), 5.49 (dd, 1H, J=2.5, 1.5 Hz), 5.42 (d, 1H, J=1.0 Hz), 5.30-5.35 (m, 2H), 4.54-4.58 (m, 1H), 4.30 (dd, 1H, J=12.5, 6.0 Hz), 4.11 , (dd, 1H, J=12.0, 2.5 Hz), 2.33 (s, 3H), 2.15 (s, 3H), 2.08 (s, 3H), 2.06 (s, 3H), 2.02 (s, 3H); HRMS (M+Cs) calcd for C21H26O9SCs 587.0352, found 587.0331.
