4594
Martinez-Pascual et al.
General Procedure for the Acetylation of Alcohols
To a solution or suspension of alcohols 1a–g (2 mmol, in all experiments)
in 5 mL of either CH2Cl2 (Entries a–d) or AcOEt (Entries e–g), Ac2O
.
(1 mL) and BF3 OEt2 (0.5 mL) were added in this order. The mixture was
stirred for 5 seconds, poured into ice/water, stirred for 15 min, and extracted
with selected solvents (2 Â 10 mL). The organic layer was washed with water
(3 Â 15 mL), 10% aqueous NaHCO3 (3 Â 15 mL) and water (3 Â 15 mL),
dried (anh. Na2SO4), and evaporated to afford the desired acetylated
product 2a–h.
1
Cholesteryl acetate, 2a. M.p 113–1158C. Lit[5] 114–1158C. H NMR: 5.4
(1H, m, H-6), 4.6 (1H, m, H-3), 2.03 (3H, s, CH3-AcO), 1.02 (3H, s, CH3-
19), 0.91 (3H, d, J20–21 ¼ 6.2 Hz, CH3-21), 0.86 (3H, d, J25–26 ¼ 6.6 Hz,
CH3-26), 0.86 (3H, d, J25–27 ¼ 6.6 Hz, CH3-27). 13C NMR: 37.06 (C-1),
27.86 (C-2), 73.95 (C-3), 38.18 (C-4), 139.45 (C-5), 122.51 (C-6), 31.93
(C-7), 31.98 (C-8), 50.06 (C-9), 36.65 (C-10), 21.14 (C-11), 39.58 (C-12),
42.36 (C-13), 57.70 (C-14), 24.38 (C-15), 28.33 (C-16), 56.14 (C-17), 11.98
(C-18), 19.42 (C-19), 35.88 (C-20), 18.83 (C-21), 36.26 (C-22), 23.95
(C-23), 39.79 (C-24), 28.10 (C-25), 22.94 (C-26), 22.69 (C-27), 170.25
(CH3COO), 21.55 (CH3COO).
5a-Cholestanyl acetate, 2b. M.p 108–1098C. Lit[5] 110–1118C. 1H NMR: 4.7
(1H, m, H-3), 2.02 (3H, s, CH3-AcO), 0.89 (3H, d, J20–21 ¼ 6.6 Hz, CH3-21),
0.85 (3H, d, J25–26 ¼ 6.6 Hz, CH3-26), 0.83 (3H, d, J25–27 ¼ 6.6 Hz, CH3-27).
13C NMR: 36.80 (C-1), 27.54 (C-2), 73.72 (C-3), 34.08 (C-4), 44.67 (C-5),
28.68 (C-6), 32.07 (C-7), 35.86 (C-8), 54.21 (C-9), 35.86 (C-10), 21.29 (C-11),
40.01 (C-12), 42.62 (C-13), 56.40 (C-14), 24.29 (C-15), 28.33 (C-16), 56.25
(C-17), 12.18 (C-18), 12.33 (C-19), 35.51 (C-20), 18.77 (C-21), 36.21 (C-22),
23.93 (C-23), 39.56 (C-24), 28.09 (C-25), 22.93 (C-26), 22.67 (C-27), 170.40
(CH3COO), 21.58 (CH3COO).
5a-Cholestan-3b,5,6b-triol triacetate, 2c. M.p 149–1518C. Lit[6] 149–
1
1508C. H NMR: 5.86 (1H, dd, J6e–7e ¼ 2.56, J6e–7a ¼ 2.94 Hz, H-6), 4.7
(1H, m, H-3), 2.81(1H, ddd, J4a–4e ¼ 13.56, J4e–3a ¼ 5.13, J4e–2e ¼ 1.8 Hz
H-4e), 2.07, 2.068, 2.0 (3H, s, 3CH3-AcO), 1.20 (3H, s, CH3-19), 0.91
(3H, d, J20–21 ¼ 6.6 Hz, CH3-21), 0.86 (3H, d, J25–26 ¼ 6.6 Hz, CH3-26),
0.85 (3H, d, J25–27 ¼ 6.6 Hz, CH3-27), 0.69 (3H, s, H-18). 13C NMR:
31.90 (C-1), 26.53 (C-2), 69.93 (C-3), 30.17 (C-4), 86.55 (C-5),
69.46 (C-6), 31.34 (C-7), 30.17 (C-8), 45.23 (C-9), 39.85 (C-10), 21.14
(C-11), 39.72 (C-12), 42.71 (C-13), 55.85 (C-14), 24.08 (C-15), 28.20
(C-16), 56.07 (C-17), 12.30 (C-18), 17.16 (C-19), 35.76 (C-20), 18.72