A suspension of methyltriphenylphosphonium bromide (1.85 g, 5.18 mmol) in tetrahydrofuran (35 mL) was treated with n-BuLi (1.9 ml, 2.5M) for 30 min at 0° C., and followed by addition of tert-butyl (3aR,5S,6S,7R,7aR)-5-formyl-6,7-bis(4-methoxybenzyloxy)-5,6,7,7a-tetrahydro-3aH-pyrano[3,2-d]thiazol-2-yl(methyl)carbamate (44) prepared from compound 28 by a procedure identical to that described for the conversion of 10 to 11) (0.6 g, 1.05 mmol) in THF (5 mL). The resulting solution was stirred overnight at room temperature, quenched by water (25 mL), and extracted with dichloromethane (3×25 ml). The combined organic layers were dried over magnesium sulfate and concentrated under vacuum to give a residue, which was purified by a silica gel column, eluted with 20% ethyl acetate in petroleum ether to give crude compound 45 as a yellow oil (220 mg, purity 50% by LC-MS). (ES, m/z): [M+H]+ 571.0.
