Investigation on the Favorable Formation of 5α-Cholestan-3α-ol and 5-Cholesten-3α-ol by Catalytic Hydrogenation

Abstract

Catalytic hydrogenation of 5α-cholestan-3-one was investigated to examine the factors influencing the selective formation of the axial 3α-ol and it has been found that the most satisfactory yield of 3α-ol is realized using Urushibara nickel A, the nickel catalyst treated by acid, in hydrocarbon solvents at lower temperatures under high pressure. Preparation of epicholestanol and epicholesterol by this method is described.

Stereocontrolled catalytic hydrogenations of 3-oxocholestanes and some related compounds to the corresponding axial 3-alcohols

“…The ir spectra were measured on a JASCO IR-G spectrometer using KBr discs. The product ratios were determined with a Shimadzu GC-4APFgas chromatograph by using either a The catalysts used were prepared according to the procedure described previously (3). In order to remove the water completely from the catalyst surface, the crystallites, which were thoroughly washed wlth water and then with 1-BuOH, were suspended once in the solvent by means of an ultrasonic cleaner, then precip~tated by centrifugation, and separated out from the liquid by decantation.…”

“…5P-Cholestan-3-one (100 mg) was hydrogenated with U-Co-A (freshly prepared from 1.5 g of precipitated cobalt) in methanol (3 mL) for 2.5 h in a similar manner to that with the 5a-ketone. The product was purified by column chromatography on silica gel with hexane-ether Hydtogencr!rotrs of 5-C/1o/es!er1-3-o11e (5) at1d5a-Cl1oles!-6-et?-otld -7-en-3-ones (6 atld 7) Preparation of 5-cholesten-3a-ol (epicholesterol) (8) from 5-cholesten-3-one uslng U-Ni-A in cyclohexane was presented In a prevlous report (3). The crude crystals gave 5-cholesten-3a-ol (8) (92% yleld) when they were chromatographed on sllica gel uslng hexane-ether(9.1); mp 139-140°C (lit.…”

“…In neutral solvents, nearly equal amounts of isomeric alcohol are frequently obtained (11); the reason proposed is that the attack of hydrogen occurs equally from either side of the molecule in those compounds in which there is little difference in steric hindrance around the carbonyl group. However, the preponderance of steroid axial 3-alcohols obtained by catalytic hydrogenation using neutral solvents under mild conditions (1)(2)(3)(4)(5)(6) suggests that this reductive technique will provide a convenient route for preparing axial 3-01s because of the ease of the procedure and the high selectivity for less stable axial alcohols. Furthermore, the data collected, which contravene the general tendency ,' are helpful in understanding the stereochemistry of catalytic hydrogenation of unhindered alicyclic ketones.…”