A
50-ml., round-bottomed flask equipped with a
magnetic stirring bar and a
20-ml. calibration mark (Note
1) is charged with
970 mg. (2.51 mmoles) of cholest-4-en-3β-ol (Note
2).
Ethyl vinyl ether is distilled into the flask to the 20-ml. mark (Note
3). The mixture is stirred to effect solution before
820 mg. (2.55 mmoles) of mercury(II) acetate (Note
4) is added to the reaction mixture. The flask is fitted with a
reflux condenser connected to a
gas-inlet tube and flushed with
argon. The reaction mixture is then stirred and heated (Note
5) at reflux under a positive
argon pressure for 17 hours. After the solution has cooled to room temperature,
0.062 ml. (1.1 mmoles) of glacial acetic acid (Note
6) is added, and stirring is continued for 3 hours. The reaction mixture is poured into a preshaken mixture of
150 ml. of petroleum ether (Note
7) and
50 ml. of 5% aqueous potassium hydroxide. The aqueous phase is extracted with
50 ml. of petroleum ether, and the combined extracts are washed with three
50-ml. portions of a 20% aqueous sodium chloride, dried over anhydrous
sodium carbonate, filtered and evaporated at reduced pressure (Note
8), giving 1.11 g. of an oil which, upon filtration through
5 g. of silica gel (Note
9) with
200 ml. of petroleum ether, affords
0.81 g. of the
cholestenyl vinyl ether as a clear, colorless oil. If desired, crystallization of this oil from
10 ml. of acetone will give
0.74 g. (
71%) of the
vinyl ether as colorless prisms, m.p.
55–56.5° (Note
10).
Alternatively, the crude
vinyl ether (0.81 g.) is transferred with
petroleum ether into a
50-ml., round-bottomed flask fitted with a long gas-inlet tube. After the
petroleum ether is removed at reduced pressure (Note
8), the flask is filled with
argon and heated (Note
11) under a positive
argon pressure at 220–225° for 5 hours; little or no bubbling should occur. After cooling, the oil is chromatographed on
75 g. of silica gel using
10% diethyl ether in petroleum ether as the elution solvent (Note
7), (Note
9), (Note
12). The first 175 ml. of eluant contains side products and is discarded; elution with another 175 ml. of the solvent gives
0.45–0.55 g. (
50–53% overall yield from
cholest-4-en-3β-ol) of
5β-cholest-3-ene-5-acetaldehyde as white prisms, m.p.
66.5–68° (Note
10).