Reaction Steps
To solution of 32a (1.28 g, 2.25 mmol) in 4:1 THF/H2O (25 mL) was added p-TsOH (111.0 mg, 0.6 mmol). After heating at 70° C. 5 h, the reaction mixture was poured into a cold (0° C.) sat. NaHCO3 aq solution (12 mL) and then extracted with EtOAc. The combined organic layers were washed with brine, dried over MgSO4 and concentrated under reduced pressure. The crude product was purified by flash chromatography (gradient hexane to hexane/EtOAc 84:16) to give 67 (793.2 mg, 76%) as a clear oil: 1H NMR (400 MHz, CDCl3) □ 0.90 (d, J=5.8 Hz, 3H), 1.0 (d, J=6.9 Hz, 3H), 1.24 (s, 6H), 1.97-2.04 (m, 1H), 3.24 (dd, J=4.8 and 9.2 Hz, 1H), 3.34 (m, 1H), 3.42 (dd, J=5.8 and 9.2 Hz, 1H), 4.35 (d, J=11.9 Hz, 1H), 4.39 (d, J=11.9 Hz, 1H), 4.64 (d, J=11.9 Hz, 1H), 4.69 (d, J=11.9 Hz, 1H), 4.96 (t, J=6.0 Hz, 1H), 7.19-7.28 (m, 5H), 9.49 (s, 1H); 13C NMR (100 MHz, CDCl3) −12.0, 14.8, 19.5, 19.6, 35.4, 43.3, 60.9, 71.1, 73.3, 80.37, 94.5, 127.7, 127.8, 128.3, 137.9, 154.1, 201.0, 210.1; IR (film, NaCl, cm−1) 2973, 2880, 1758, 1701, 1453, 1380, 1248; LRMS (ESI) calcd for C21H27O6Cl3Na [M+Na+] 503.0, found 503.0; [α]23D=−18.5 (c=0.8, CHCl3).
