To a cold solution of 37 (100 mg, 0.18 mmol) in acetonitrile (20 mL) at −5° C. was added a solution of Hg(OAc)2 (68 mg, 0.21 mmol) in water (10 mL) dropwise. After stirred at 0° C. for 4 h, the reaction mixture was treated with potassium iodide (40 mg, 0.24 mmol) in water (1.6 mL) for 10 min. The reaction solution was quenched with water, extracted with dichloromethane (40 mL), and dried over MgSO4. Removal of solvents gave crude 2-((3aR,5R,6R,7R,7aR)-6,7-bis(4-methoxybenzyloxy)-2-(dimethylamino)-5,6,7,7a-tetrahydro-3aH-pyrano[3,2-d]thiazol-5-yl)acetaldehyde. To a solution of the crude product in dry THF (20 mL) was added NaBH4 (16 mg, 0.42 mmol) at 0° C. in portions. After stirred at 0° C. overnight, the reaction solution was quenched with water (25 mL) and extracted with ethyl acetate (2×20 mL). The combined organic phases were washed with saturated aqueous NH4Cl, dried over MgSO4, and concentrated to give a residue, which was purified by silica gel chromatography, eluted with 20-50% ethyl acetate in petroleum ether to give the product 38 as a light yellow oil (50 mg, 48%). (ES, m/z)[M+H]+ 503.0; 1H NMR (300 MHz, CDCl3) δ 7.15-7.35 (m, 4H), 6.84-6.98 (m, 4H), 6.28 (d, J=6.3 Hz, 1H), 4.45-4.89 (m, 4H), 4.18 (t, J=5.7 Hz, 1H), 3.94 (t, J=4.8 Hz, 1H), 3.87-3.91 (m, 1H), 3.78 (s, 6H), 3.56-3.65 (m, 3H), 2.92 (s, 6H), 1.89-1.98 (m, 1H), 1.62-1.73 (m, 1H).
