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To a solution of 16 (240 mg, 0.6 mmol) in THF (5 mL) was added benzylamine (100 μL, 0.9 mmol) followed by NaHB(OAc)3 (153 mg, 0.72 mmol). The reaction was allowed to stir for an additional 3 h then partitioned between EtOAc (100 mL) and brine (50 mL). The aqueous layer was extracted with EtOAc (50 mL). The combined organic layers were dried over Na2SO4 and concentrated. The crude product was purified by flash column chromatography (EtOAc:hexanes, 1:2-1:1) to give 19 (270 mg, 0.55 mmol, 92%) as a colorless oil: 1H NMR (500 MHz, CDCl3) δ 0.99-1.01 (d, J=6.5 Hz, 3H), 1.09-1.11 (d, J=6.5 Hz, 3H), 2.13 (s, 6H), 2.37 (s, 3H), 2.76-2.85 (ddd, J=4.5, 5.0, 12.5, Hz, 1H), 2.98-3.08 (ddd, J=5.5, 14.0, 15.5, Hz, 1H), 3.49-3.52 (m, 1H), 3.81 (s, 2H), 3.82-3.89 (m, 1H), 4.04-4.08 (dd, J=6.0, 12.5, Hz, 1H), 4.09-4.12 ((dd, J=5.5, 13.0, Hz, 1H), 4.86-4.89 (m, 1H), 5.13-5.15 (dd, J=1.0, 10.0, Hz, 1H), 5.23-5.28 (dd, J=1.5, 17.0, Hz, 1H), 5.86-5.91 (m, 3H), 6.85 (s, 1H), 7.00 (s, 1H), 7.20-7.27 (m, 2H), 7.27-7.35 (m, 3H); 13C NMR (125 MHz, CDCl3) δ 13.6, 21.2, 21.8, 21.9, 35.1, 47.6, 49.9, 54.0, 68.0, 71.4, 79.4, 106.8, 117.2, 120.3, 123.4, 127.2, 128.4, 128.6, 128.8, 134.9, 140.4, 149.5, 151.7, 159.4, 173.0; LCQ-MS (M+H+) calcd for C30H40N3O3 490. found 490; LC-TOF-MS (M+H+) calcd for C30H40N3O3 490.30697. found 490.30644.
