To a mixture of ((3aR,5R,6S,7R,7aR)-6,7-bis(4-methoxybenzyloxy)-2-(dimethylamino)-5,6,7,7a-tetrahydro-3aH-pyrano[3,2-d]thiazol-5-yl)methanol (500 mg, 1.0 mmol), TBAB (16.5 mg, 0.05 mmol), KHCO3 (461 mg, 4.6 mmol) and TEMPO (8 mg, 0.05 mmol) in dichloromethane (25 mL) and H2O (5 mL) was added NBS (201 mg, 1.13 mmol) at 15° C. After stirred for 30 min, the reaction mixture was quenched by saturated Na2SO3 (5 mL). The organic layer was dried over anhydrous magnesium sulfate and condensed to provide a residue, which was purified by silica gel column, eluted with 20-30% ethyl acetate in dichloromethane to give compound 11 as a yellow syrup (320 mg, 75% pure). (ES, m/z): [M+H]+ 487.0. 1H NMR (300 MHz, CDCl3) δ 9.61 (s, 1H), 7.22-7.34 (m, 4H), 6.83-6.92 (m, 4H), 6.11-6.13 (d, J=6.0 Hz, 1H), 4.17-4.67 (m, 8H), 3.83 (s, 6H), 3.00-3.04 (s, 6H).
