Reaction Steps
To a solution of (3aS,4R,5R,6S,7aS)-4,5-bis(benzyloxy)-N-ethyl-6-(fluoromethyl)-3a,4,5,6,7,7a-hexahydrobenzo[d]oxazol-2-amine (209 mg, 0.507 mmol) in DCM (5 mL) at −78° C. was added a solution of BCl3 in DCM (1.0 M, 1.27 mL, 1.27 mmol). The mixture was slowly warmed up to 0° C. and stirred at this temperature for 5 h. The reaction was cooled to −78° C. again and a 1:1 mixture of MeOH-DCM (10 mL) was added dropwise to quench the reaction. Solvents were evaporated and the residue was treated with MeOH for three more times. The crude product was purified by silica gel column chromatography, eluted with 5%-15% 2 M NH3 MeOH solution in DCM to give the product (3aR,4R,5R,6S,7aS)-2-(ethylamino)-6-(fluoromethyl)-3a,4,5,6,7,7a-hexahydrobenzo[d]oxazole-4,5-diol (86.0 mg, 73%) as a white solid. MS m/z 233.2 (M+1, 100%); 1H NMR (400 MHz, MeOD) δ 4.60 (dd, J=9.0 Hz, 4.4 Hz, 0.5H), 4.45-4.51 (m, 2H), 4.35 (dd, J=9.0 Hz, 2.5 Hz, 0.5H), 3.47 (t, J=7.1 Hz, 1H), 3.13-3.22 (m, 2H), 3.06-3.12 (m, 2H), 2.12-2.21 (m, 1H), 1.65-1.80 (m, 2H), 1.06 (t, J=7.3 Hz, 3H); 13C NMR (100 MHz, MeOD) δ 163.88, 84.63 (d, J=165.6 Hz), 80.81, 80.65, 71.86 (d, J=4.8 Hz), 68.43, 39.40 (d, J=18.6 Hz), 38.23 (d, J=2.4 Hz), 28.14 (d, J=3.8 Hz), 15.24.
