A suspension of -(3aR,5R,6S,7R,7aR)-2-(dimethylamino)-5-(hydroxymethyl)-5,6,7,7a-tetrahydro-3aH-pyrano[3,2-d]thiazole-6,7-diol (0.800 g, 3.23 mmol) and anhydrous ZnCl2 (1.00 g, 7.35 mmol) in benzaldehyde (5 mL) was stirred at room temperature overnight. DCM (50 mL) and satd. aqueous NaHCO3 (50 mL) was added, and mixture was stirred for 20 min. The solid was filtered off, and the organic layer was collected from the filtrate. The aqueous layer was extracted with DCM (2×50 mL), and the combined extract was dried over anhydrous Na2SO4. After filtration the solvent was evaporated under reduced pressure, and the residue was purified on silica gel by flash column chromatography (1.0 M NH3 in MeOH/DCM, 3:100), affording -(3aR,4aR,8aS,9R,9aR)-2-(dimethylamino)-7-phenyl-3a,4a,5,8a,9,9a-hexahydro-[1,3]dioxino[4′,5′:5,6]pyrano[3,2-d]thiazol-9-ol as a pale yellow solid (0.76 g, 70%). 1H NMR (400 MHz, CDCl3) δ 7.51-7.48 (m, 2H), 7.40-7.34 (m, 3H), 6.39 (d, J=6.6 Hz, 1H), 5.58 (s, 1H), 4.31 (dd, J=5.1, 10.4 Hz, 1H), 4.10-4.03 (m, 2H), 3.86 (dd, J=8.2, 9.5 Hz, 1H), 3.76 (t, J=10.4 Hz, 1H), 3.59 (t, J=9.5 Hz, 1H), 3.00 (s, 6H).
