Reaction Steps
To a solution of tert-butyl ((3aR,5S,6R,7S,7aR)-5-acetyl-6-(benzyloxy)-7-fluoro-5,6,7,7a-tetrahydro-3aH-pyrano[3,2-d]thiazol-2-yl)(methyl)carbamate (0.310 g, 0.704 mmol) and TMSCF3 (0.299 g, 2.10 mmol) in anhydrous THF (12 mL) was added TBAF (1.0 M in THF, 0.040 mL, 0.040 mmol). After addition the reaction mixture was stirred at room temperature for 16 h. Another batch of TBAF (1.0 M in THF, 1.2 mL, 1.2 mmol) was added at 0° C., and the mixture was stirred at room temperature for another 2 h. The reaction solution was then diluted with brine (50 mL), and extracted with EtOAc (2×30 mL). The combined extract was dried over anhydrous Na2SO4. After filtration the solvent was evaporated under reduced pressure, and the residue was purified and separated on silica gel by automatic flash column chromatography (EtOAc/hexanes, 1:10 to 1:2), affording tert-butyl ((3aR,5S,6R,7S,7aR)-6-(benzyloxy)-7-fluoro-5-((R)-1,1,1-trifluoro-2-hydroxypropan-2-yl)-5,6,7,7a-tetrahydro-3aH-pyrano[3,2-d]thiazol-2-yl)(methyl)carbamate (0.178 g, 50%) as a white foam, 1H NMR (major isomer) (400 MHz, CDCl3) δ 7.37-7.28 (m, 5H), 6.18 (d, J=7.7 Hz, 1H), 5.08 (td, J=4.3, 45.6 Hz, 1H), 4.92 (d, J=10.7 Hz, 1H), 4.67-4.60 (m, 1H), 4.49 (d, J=10.7 Hz, 1H), 4.27-4.22 (m, 1H), 3.66-3.92 (m, 1H), 3.28 (s, 3H), 3.05 (s, br. 1H), 1.54 (s, 9H), 1.38 (s, 3H); and tert-butyl ((3aR,5S,6R,7S,7aR)-6-(benzyloxy)-7-fluoro-5-((S)-1,1,1-trifluoro-2-hydroxypropan-2-yl)-5,6,7,7a-tetrahydro-3aH-pyrano[3,2-d]thiazol-2-yl)(methyl)carbamate (0.136 g, 38%) as a white foam, 1H NMR (minor isomer) (400 MHz, CDCl3) δ 7.37-7.28 (m, 5H), 6.19 (d, J=7.7 Hz, 1H), 5.05 (td, J=4.3, 45.7 Hz, 1H), 4.94 (d, J=10.7 Hz, 1H), 4.64-4.60 (m, 1H), 4.49 (d, J=10.7 Hz, 1H), 4.26-4.24 (m, 1H), 3.90 (d, J=7.5 Hz, 1H), 3.29 (s, 3H), 3.25 (s, br. 1H), 1.54 (s, 9H), 1.37 (s, 3H). The stereochemistry for each isomer was assigned randomly.
