To a solution of diisopropyl ester 10 (140 mg, 0.31 mmol) in toluene (5 mL) at −78° C. was added dropwise a solution of Dibal-H (1.0 M in toluene, 620 μL, 0.62 mmol) along the side of the flask over a period of 15 min. The reaction was maintained at −78° C. during the addition and allowed to react at the same temperature for 7 h. To the resulting solution at −78° C., MeOH (100 μL) was added dropwise along the side of the flask to quench the reaction. The reaction mixture was warmed to −20° C. and poured directly onto a vigorously stirring Rochelle's solution (potassium sodium tartrate solution, 5 mL). The viscous solution was allowed to stir for an additional 30 min then settled down to two clear phases. The organic layer was separated, and the aqueous layer was extracted with ether (3×5 mL). The combined organic layers were dried over Na2SO4 and concentrated. The crude product was purified by flash column chromatography (EtOAc/hexanes, 1:9-1:4) to give 16 (75 mg, 0.19 mmol, 62%) as a colorless oil: 1H NMR (500 MHz, CDCl3) δ 1.11-1.13 (d, J=6.0, 3H), 1.16-1.18 (d, J=6.5, 3H), 2.11 (s, 6H), 2.40 (s, 3H), 3.01-3.04 (dd, J=6.5, 14.5 Hz, 1H), 3.28-3.33 (dd, J=8.0, 15.0 Hz, 1H), 3.60-3.73 (ddd, J=4.0, 7.0, 11.5 Hz, 1H), 3.85-3.86 (dd, J=1.0, 4.5 Hz, 1H), 4.03-4.06 (dd, J=6.0, 13.0 Hz, 1H), 4.21-4.25 (dd, J=6.0, 12.5 Hz, 1H), 4.96-4.98 (m, 1H), 5.19-5.22 (dd, J=1.5, 10.5 Hz, 1H), 5.24-5.28 (dd, J=2.0, 17.5 Hz, 1H), 5.86-5.91 (m, 3H), 6.88 (s, 1H), 7.03 (s, 1H), 9.75-9.77 (d, J=1.0 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 13.5, 21.2, 22.0, 35.4, 46.8, 69.1, 72.7, 83.1, 106.9, 107.0, 118.6, 120.7, 123.7, 128.7, 133.9, 149.9, 151.9, 158.5, 171.0, 202.5; LCQ-MS (M+H+) calcd for C23H31N2O4 399. found 399; LC-TOF-MS (M+H+) calcd for C23H31N2O4 399.22838. found 399.22859.
