1514
M. MUSHFIQ ET AL.
band was absent; therefore, it can be formulated as 6a-acetylcholest-4-en-3-one-
10,3-dioxime (15).
Baeyer–Villiger oxidation of 6a-acetylcholest-4-en-3-one (14) afforded methyl
4
a-5-epoxy-5a-cholestan-3-oxo-6a-carboxylate (16) and methyl 3-oxo-4aa,5-
epoxy-A-homo-5-a-cholestan-4-oxo-6-a-carboxylate (17). A similar attempt using
propionic anhydride–zinc chloride with cholest-5-ene-3one (2) gave the propionoxy
derivative (18). The data (Table 1) are in full agreement with the structure being 6b-
propionoxy-cholest-4-ene-3-one (18).
Similar treatment to 3b-chlorocholest-5-ene (1a)[14] resulted in simple replace-
ment of chlorine by the acetoxy group, whereas the 3b-acetoxy cholest-5-ene (1b)[15]
completely refused to react under the conditions.
EXPERIMENTAL
General Procedure for Acylation
A solution of cholest-5-ene (1) (2.5 g, 0.007 mol) in carbon tetrachloride (40 ml)
was added in small portions to a well-stirred mixture of acetic anhydride (20 ml) and
dry zinc chloride (1 g, 0.007 mol) over a period of 40–45 min. The temperature of the
reaction mixture was maintained between 0 and 5 ꢀC by external cooling. After the
addition was complete, stirring was continued for 8 h at room temperature under
anhydrous conditions. The reaction mixture was then poured into ice-cooled water.
The organic matter was extracted with carbon tetrachloride; washed successively
with water, sodium bicarbonate solution (5%), and water; and then dried over anhy-
drous sodium sulfate. Evaporation of solvent under reduced pressure afforded an oil,
which was chromatographed over silica gel (50 g). The column was eluted with light
petroleum ether to provide different fractions with increasing proportions of ether as
shown in Table 2.
Baeyer–Villiger oxidation was carried out according to the literature
procedure,[16] and the products are given in Table 2.
Oximation of the ketones as reported was carried out following the procedure
reported in the literature,[17] and the products are listed in Table 2.
REFERENCES
1. Hoffmann, M. R.; Tsushima, T. Acylation of olefins by acetyl hexachloroantimonate:
Selective formation of b,c-unsaturated ketones under kinetic control and mechanistic
rationale as an ene reaction. J. Am. Chem. Soc. 1977, 99(18), 2008. See also Kondakov,
I. L. Zh. Russ., Fiz-Khim-O-va. 1892, 24, 309 and Blanc, G. Bull. Soc. Chim. Fr. 1898,
19, 699.
2. Olah, G. A. Friedel–Crafts and Related Reactions; John Wiley: New York, 1964; vol. 3.
3. Groves, J. K. The Friedel–Crafts acylation of alkenes. Chem. Soc. Rev. 1972, 1, 73.
4. Deno, N. C.; Chafetz, H. Acetylation of 1-methylcyclohexene. J. Am. Chem. Soc. 1952,
74, 3940.
5. (a) Groves, J. K.; Jones, N. Aliphatic Friedel–Crafts reactions, part VI: Preparation of bc
unsaturated ketones by the acetylation of substituted cyclohexenes. J. Chem. Soc. (C)
1968, 2215; (b) Groves, J. K.; Jones, N. Aliphatic Friedel–Crafts reactions, part VIII: