Reaction Steps
To a solution of 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 (minor isomer from the TMSCF3 addition step) (0.136 g, 0.277 mmol) and PMB (0.10 g, 0.68 mmol) in dry DCM (5 mL) at −78° C. under N2, was added BCl3 (1.0 M in DCM, 2.0 mL, 2.0 mmol). The mixture was stirred for ˜4 h while the temperature of the cooling bath slowly warmed to room temperature. The reaction mixture was cooled at −78° C., quenched with mixed MeOH/DCM, and then concentrated to dryness. The residue was purified on silica gel by flash column chromatography (1.0 M NH3 in MeOH/DCM, 1:13), affording (3aR,5S,6R,7S,7aR)-7-fluoro-2-(methylamino)-5-((S)-1,1,1-trifluoro-2-hydroxypropan-2-yl)-5,6,7,7a-tetrahydro-3aH-pyrano[3,2-d]thiazol-6-ol as a white solid (0.081 g, 92%). 1H NMR (600 MHz, CD3OD) δ 6.34 (d, J=6.7 Hz, 1H), 4.84 (ddd, J=3.5, 5.0, 46.3 Hz, 1H), 4.63-4.60 (m, 1H), 4.36-4.33 (m, 1H), 3.75 (d, J=6.9 Hz), 2.88 (s, 3H), 1.35 (s, 3H); 13C NMR (150.9 MHz, CD3OD) δ 165.25, 127.26 (q, J=287.0 Hz), 90.46 (d, J=9.1 Hz), 89.55 (d, J=186.4 Hz), 79.12 (d, J=4.0 Hz), 75.77 (q, J=27.3 Hz), 73.26 (d, J=16.6 Hz), 67.35 (d, J=16.9 Hz), 30.96, 18.72; MS, (ES, m/z) [M+H]+ 319.1.
