Reaction Steps
Solution of hydroxy ketone 3 (1.64 g, 5.8 mmol) in anhydrous pyridine (12 mL) and acetic anhydride (5.5 mL) was stirred for 3 h at room temperature. It was poured into water and extracted with ethyl acetate. The organic layer was washed with saturated NaHCO3, saturated CuSO4 and water, dried (MgSO4), and evaporated to give an oily residue which was dissolved in hexane/ethyl acetate (8:2) and filtered through short path of silica gel. Evaporation of solvents gave pure crystalline acetate 4 (1.51 g, 81%). Analytical sample was obtained by recrystallization from hexane/ethyl acetate. 4: m.p. 134-7° C.; [α]24D−78° (c 1.00 CHCl3); 1H NMR (400 MHz, CDCl3) δ 0.046 and 0.141 (3H and 3H, each s, 2×SiCH3), 0.901 (9H, s, Si-t-Bu), 2.17 (3H, s, CH3CO), 2.28 (1H, dd, J=12.2, 10.4 Hz, 2α-H), 2.32 (1H, d, J=12.1 Hz, 8α-H), 2.65 (1H, ddd, J=12.2, 8.8, 3.9 Hz, 2β-H), 3.56 (1H, ddd, J=12.1, 6.9, 3.9 Hz, 8β-H), 4.58 (1H, dd, J=10.4, 8.8 Hz, 3β-H), 4.80 (1H, d, J=6.9 Hz, 5α-H); 13C NMR (125 MHz) δ −5.8 (Si—CH3), −4.9 (Si—CH3), 18.2 [C(CH3)3], 20.9 (CH3—C═O), 25.6 [C(CH3)3], 38.3 (C8), 40.3 (C2), 70.4 (C3), 75.3 (C1), 78.4 (C5), 169.1 (CH3—C═O), 171.5 (C═O), 201.8 (C4); MS (EI) m/z (relative intensity) 328 (M+, 6), 271 (100), 256 (38), 229 (54), 211 (53); HRMS (ESI) exact mass calcd for C11H15O6Si (M+−t-Bu) 271.0638, measured 271.0646; Anal. Calcd for C15H24O6Si: C, 54.86, H, 7.37. Found: C, 54.88, H, 7.37.
