Reaction Steps
To a solution of 7-Benzyloxy-5-hydroxy-1,1-diisopropoxy-2,2,4,6-tetramethyl-heptan-3-one 32 (1.0 g, 2.4 mmol) and pyridine (0.8 mL, 7.3 mmol) in CH2Cl2 (10.0 mL) at 0° C. was added 2,2,2-trichloroethyl chloroformate (668.0 μL, 4.9 mmol) and the mixture was then allowed to warm to rt. After 1 h, the reaction mixture was quenched with brine and then extracted with CH2Cl2. The combined organic layers were dried over MgSO4 and concentrated under reduced pressure. The crude product was purified by flash chromatography (gradient hexane to hexane/EtOAc 93:7) to give 32a (1.285 g, 92%) as a clear oil: 1H NMR (400 MHz, CDCl3) δ 1.03-1.09 (m, 12H), 1.15 (d, J=1.8 Hz, 3H), 1.17 (d, J=1.9 Hz, 3H), 1.19-1.21 (m, 6H), 1.97-2.11 (m, 1H), 3.2 (dd, J=6.2 and 9.0 Hz, 1H), 3.54 (dd, J=4.8 and 9.1 Hz, 1H), 3.57-3.60 (m, 1H), 3.82 (qd, J=3.6 and 5.9 Hz, 2H), 4.47 (s, 2H), 4.57 (s, 1H), 4.72 (d, J=11.9 Hz, 1H), 4.81 (d, J=11.9 Hz, 1H), 5.08 (t, J=6.0 Hz, 1H), 7.29-7.35 (m, 5H); 13C NMR (100 MHz, CDCl3) δ 11.9, 15.0, 18.8, 21.4, 21.7, 22.3, 23.2, 23.4, 35.7, 42.5, 53.4, 53.9, 69.4, 70.9, 71.4, 73.3, 81.3, 94.7, 103.4, 127.5, 127.6, 128.2, 138.2, 154.0, 215.6; IR (film, NaCl, cm−1) 2966, 1760, 1698, 1247; LRMS (ESI) calcd for C27H41O7Cl3Na [M+Na+] 605.2, found 605.2; [α]23D=−20.4 (c=1.0, CHCl3.
