A mixture of tert-butyl (3aR,5R,6S,7R,7aR)-5-(hydroxymethyl)-6,7-bis(4-methoxybenzyloxy)-5,6,7,7a-tetrahydro-3aH-pyrano[3,2-d]thiazol-2-yl(methyl)carbamate (1 g, 1.74 mmol), KHCO3 (780 mg, 7.8 mmol), TBAB (28 mg, 0.09 mmol) and TEMPO (14 mg, 0.09 mmol) in dichloromethane (30 mL) and H2O (6 mL) was treated with NBS (620 mg, 3.5 mmol) overnight at room temperature. The reaction mixture was adjusted to acidic (pH at 3) with hydrochloric acid, and then extracted with dichloromethane (3×20 mL). The combined organic layers were dried over anhydrous sodium sulfate and concentrated under vacuum to provide a residue, which was purified by a silica gel column, eluted with 20˜50% ethyl acetate in petroleum ether to give compound 29 as a white solid (600 mg, 58%). (ES, m/z): [M+H]+ 589.0, 1H NMR (300 MHz, CDCl3) δ 7.25-7.32 (m, 2H), 6.85-6.90 (m, 2H), 6.08-6.10 (d, J=6.3 Hz, 1H), 4.50-4.62 (m, 5H), 4.22-4.29 (m, 2H), 3.97 (m, 1H), 3.81 (s, 6H), 3.34 (s, 3H), 1.54 (s, 9H).
