882
HETEROCYCLES, Vol. 77, No. 2, 2009
(CH), 27.1 (CH3, 3C), 25.4 (CH3), 22.4 (CH3), 20.4 (CH3), 19.3 (C), 12.4 (CH3). IR νmax 3049, 2962,
1704, 1589, 1471, 1427, 1187, 1111, 741, 702 cm-1. MS (EI, 70 eV, 30 °C): m/z: 323, 280, 241, 223, 183,
141, 84. HRMS (70 eV, 30 °C): m/z calcd for C20H25O2Si (M – t-Bu) : 325.1624, found: 325.1631.
Synthesis of 1-(tert-butyldiphenylsilanyloxy)-6-hydroxy-2,3,3,7,8-pentamethyl-8-(2-methyl-1,3-
dioxolan-2-yl)nonan-4-one (20)
To a solution of freshly prepared LDA (0.39 M, 10.0 mL, 3.92 mmol, 1.50 eq) in THF (8 mL) was added
slowly ketone (14b) (1.00 g, 2.61 mmol, 1.00 eq) in THF (8 mL) with stirring at -78 °C. Stirring of the
slightly yellow solution was continued for additional 30 min. Then aldehyde 13 (730 mg, 3.92 mmol,
1.50 eq) in THF (6 mL) was added at once. The solution was kept at -78 °C for 2 ½ h (TLC) and then
quenched by the addition of MeOH and solid NH4Cl. The mixture was allowed to warm up and diluted
with Et2O. Water was added and the layers were separated. The aqueous layer was extracted three times
with Et2O and the combined organic layer was washed with water and brine, dried over MgSO4, filtered
and concentrated in vacuo. The crude product was purified by column chromatography (hexane/EtOAc =
10:1) to yield 20 (1.04 g, 70%) as a colorless oil.
Mr = 568.86, C34H52O5Si. Rf = 0.40 (hexane/EtOAc = 5:1). d.e. ~ 5:4 (determined by 1H NMR)
major diastereomer:
1H NMR (400 MHz, CDCl3): δ 7.65 (m, 4H), 7.39 (m, 6H), 4.65 (m, 1H), 3.92 (m, 4H), 3.54 (dd, 1H, J
= 10.2, 5.4 Hz), 3.41 (m, 1H), 2.95 (d, 1H, J = 3.7 Hz), 2.72 (dd, 1H, J = 19.3, 8.5 Hz), 2.38 (dd, 1H, J =
17.3, 4.3 Hz), 2.13 (m, 1H), 1.43 (m, 1H), 1.04 (s, 9H), 1.00 (m, 18H), 0.89 (m, 3H). 13C NMR (101
MHz, CDCl3): δ 215.1 (C), 135.8 (CH, 4C), 133.7 (C, 2C), 129.8 (CH, 2C), 127.8 (CH, 4C), 114.8 (C),
67.4 (CH), 66.0 (CH2), 64.9 (CH2), 64.5 (CH2), 49.7 (C), 45.1 (C), 43.9 (CH), 43.1 (CH2), 41.2 (CH),
27.0 (CH3, 3C), 23.6 (CH3), 21.6 (CH3), 21.1 (CH3), 20.7 (CH3), 20.1 (CH3), 19.3 (C), 12.5 (CH3), 9.1
(CH3).
minor diastereomer :
1H NMR (400 MHz, C6D6): δ 7.65 (m, 4H), 7.39 (m, 6H), 4.65 (m, 1H), 3.92 (m, 4H), 3.60 (dd, 1H, J =
10.1, 5.2 Hz), 3.41 (m, 1H), 3.03 (d, 1H, J = 3.5 Hz), 2.76 (dd, 1H, J = 17.2, 8.7 Hz), 2.26 (dd, 1H, J =
17.2, 3.7 Hz), 2.13 (m, 1H), 1.43 (m, 1H), 1.04 (s, 9H), 1.00 (m, 18H), 0.89 (m, 3H). 13C NMR (101
MHz, CDCl3): δ 215.8 (C), 135.7 (CH, 4C), 133.7 (C, 2C), 129.8 (CH, 2C), 127.8 (CH, 4C), 114.8 (C),
67.6 (CH), 65.9 (CH2), 64.9 (CH2), 64.5 (CH2), 49.8 (C), 45.1 (C), 43.6 (CH), 43.1 (CH2), 41.2 (CH),
27.0 (CH3, 3C), 23.4 (CH3), 21.3 (CH3), 21.1 (CH3), 20.6 (CH3), 20.1 (CH3), 19.3 (C), 12.7 (CH3), 9.0
(CH3).
IR νmax 3518, 3071, 2973, 2884, 1698, 1589, 1471, 1427, 1112, 741, 703 cm-1. MS (EI, 70 eV, 30 °C):
m/z: 553, 511, 449, 325, 239, 199, 125, 87, 55. HRMS (70 eV, 30 °C): m/z calcd for C33H49O5Si (M –