Reaction Steps
At 15° C., to a solution of (3aR,4R,5R,6R,7aS)-4,5-bis(benzyloxy)-6-((benzyloxy)methyl)-N,N-dimethyl-3a,4,5,6,7,7a-hexahydrobenzo[d]thiazol-2-amine (13) (0.950 g, 1.84 mmol) in mixed Ac2O/AcOH (10 mL/2 mL) was added anhydrous ZnCl2 (2.5 g, 18 mmol). The mixture was stirred at room temperature for 2 h and concentrated under vacuum at room temperature. The residue was diluted with DCM (50 mL) and saturated aqueous NaHCO3 (50 mL). The mixture was stirred for 30 min, and the solid was filtered off over a Celite 521 cake. The organic layer was collected from the filtrate, and the aqueous was extracted with DCM (3×30 mL). The combined extract was dried over anhydrous Na2SO4. After filtration the solvent was evaporated under reduced pressure, and the residue was dissolved in MeOH (15 mL). Anhydrous K2CO3 (0.47 g, 3.4 mmol) was added, and the mixture was stirred at room temperature for 2 h. AcOH (0.5 mL) was added and the reaction mixture was concentrated under reduced pressure at room temperature. The residue was diluted with saturated aqueous NaHCO3 (30 mL), and then extracted with DCM (3×30 mL). 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 (EtOAc, then MeOH/DCM, 1:10), affording 14 as a sticky pale yellow foam (0.36 g, 46%). 1H NMR (400 MHz, CDCl3) δ 7.44-7.41 (m, 2H), 7.36-7.24 (m, 8H), 5.02 (d, J=11.0 Hz, 1H), 4.95 (d, J=11.2 Hz, 1H), 4.70 (d, J=11.0 Hz, 1H), 4.62 (d, J=11.2 Hz, 1H), 4.31-4.28 (m, 1H), 4.11 (t, J=7.3 Hz, 1H), 3.70 (t, J=8.4 Hz, 1H), 3.64-3.62 (m, 2H), 3.35 (dd, J=8.9, 10.2 Hz, 1H), 3.00 (s, 6H), 2.23 (s, br. 1H), 2.24-2.16 (m, 1H), 2.07-2.02 (m, 1H), 1.72-1.64 (m, 1H).
