5a-cholestanone

The hydrogenation of 5a-cholestanone (58) in methanolic hydrobromic acid over platinum gives 3j5-methoxycholestane ° (61). This compound is also obtained from the palladium oxide reduction of (58) in methanol in the absence of acid. Hydrogenation of 5 -cholestanone also gives the 3j5-methoxy product under these conditions. Reduced palladium oxides are quite effective for the conversion of ketones to ethers. The use of aqueous ethanol as the solvent reduces the yield of ether. Ketals are formed on attempted homogeneous hydrogenation of a 3-keto group in methanol. ... 

Nelson and Scliut investigated the reaction of 5a-cholestanone (lb) with diazomethane in a search for a direct, one-step preparation of A-homo ketones. Using a large excess of diazomethane generated in situ from A-methyl-nitrosourea with potassium hydroxide in ether-methanol at 0°, 5a-cholestanone (lb) is converted into the 7-membered ring homolog (3b) as the predominant product. Both theoretically possible A-homo ketones can be expected with an unsymmetrically-substituted cyclohexanone such as 5a-cholestanone (lb). 

Treatment of 5a-cholestanone (lb) in this way gives a mixture from which 7-and 8-membered ring ketones can be isolated. The yields of crude ketones are A-homo-4-one (3b), 40-50% A-homo-3-one (5b), 10% and a A-bis-homo ketone 5 %. The structure of the bis-homocholestanone has not been rigorously established. 

To establish the structure of A-homo ketone (3b) Nelson and Schut repeated the TifFeneau ring enlargement of 5a-cholestanone [(Ib) (6a) (6b) -> (7)] and obtained a ketone identical with A-homo ketone (3b). 

Exercise 30-12 Reduction of the double bond of cholesterol can be carried out so as to produce either 5a- or5/3-cholestanol. Equilibration of 5a-cholestanol with a trace of 5a-cholestanone and base (Section 16-4E) gives 90% 5a-cholestanol and 10% of a stereoisomer known as epicholestanol. Similar equilibration of 5/6-cholestanol (in the presence of 5 -cholestanone) gives 10% 5/8-cholestanol and 90% of a stereoisomer of 5/3-cholestanol known as epicoprostanol. Write the configurations of each of these compounds and explain the orders of stabilities that are observed. 

Two years before Wentrup and Dahn s work Avaro et al. (1968) investigated two other a-diazo ketones in FSO3H-CDCI3-SO2. They found that 2-diazo-5a cholestanone (2.14, R = H) and its 4,4-dimethyl derivative (2.14, R = CH3) exhibit a... 

Cholestanone, 497 5a-Cholestanone, 475 A -Cholestene, 497 A -Cholestene-3d,5a-diol, 110 A -Cholestene-3/3,5(3-diol, 110 Cholesteryl benzoate, 110 Chromenes, 235-236 A -Chromens, 407 Chromic acid-Silica gel, 110 Chromic anhydride-3,5-Dimethylpyrazole complex, 110 Chromium carbonyl, 110 Chromium(III) chloride-Lithium aluminum hydride, 110-112 Chromyl chloride, 112 ... 

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