Alcohols. 196 cholestenes

The reduction of allylic systems is frequently used to generate isolated double bonds. Suitable systems are obtained from oe,jS-unsaturated ketones via allylic alcohols (ref. 185, p. 256 ref. 283, 284) for example, the preparation of A" -cholestene (135). 

The aerobic system TPAP/O /PMS/CH Cl was used to oxidise primary and secondary alcohols [28]. Oxidation of secondary alcohol functions in 3p-hydroxy-A-cholestenes,... 

Inspection of Table 6.1 shows that the classical oxidation of sterols on the alcohol at the 3-position, using acetone as oxidant, works efficiently thanks to the migration of the alkene. Thus, the oxidation of cholesterol with acetone (E0 = 129 mV) must proceed via the thermodynamically disfavoured A5-cholesten-3-one (E0 = 153 mV) that evolves to the very stable A4-cholesten-3-one (E0 = 63 mV). In fact, acetone lacks oxidizing power for the obtention of many ketones as well as for the preparation of virtually all aldehydes. 

The experimental data for oxidation of benzyl alcohol,1 aliphatic primary and secondary alcohols,2 and cholesterol3 with cetyltrimethylammonium (CTA) dichromate indicated that the reactions occur in a reverse micelle system produced by the oxidant. Michaelis-Menten-type kinetics were observed with respect to the reductants. The product of the oxidation of cholesterol depends on the solvent. In dichloromethane, the product is 7-dehydrocholesterol, whereas with dichloromethane containing acetic acid the product is 5-cholesten-3-one. A low kinetic isotope effect, k /ku = 2.81, was observed in the oxidation of methanol- this, combined with the rate data and the reverse solvent isotope effect [ (H20)/fc(D20) = 0.76], suggests that these reactions... 

Formation and /S-fission of bicyclic tertiary alkoxyl radicals from the corresponding alcohols are well known [38] [40]. The treatment of 5a-cholestane-3/3,5-diol-3-acetate, VII/70, and the 5/3-alcohol, VII/71, respectively (Scheme VII/15), with one molar equivalent of lead tetraacetate in the presence of anhydrous calcium carbonate gives radical fragmentation reactions. The products are the two (E)- and (Z)-3/3-acetoxy-5,10-seco-l(10)-cholesten-5-ones (VII/72 + VII/73) [40]. The ratio of VII/73 VII/72 is 63 10 [41] [42] [43]. 

The diaxial 2/ -acetylamino-3/ -bromocholestane, obtained in situ from 2-cholestene, underwent direct cyclization under the reaction conditions, to give the corresponding . v-4,5-dihydrooxa-zole, which, in the presence of an excess of base, was converted to the cw-amido alcohol 1542. 

The systematic study of nucleophilic substitutions of steroid alcohols and halides, pursued by Shoppee since 1946 [47], has yielded many examples of reactions which proceed with stereochemical inversion (Walden Inversion) [48] at the reaction centre. Acetolysis of the epimeric 3-chloro-5a- [4 ] and 3-chloro-5/ -cholestanes [4g] with potassium acetate in acetic acid gives 3-acetoxy derivatives of inverted configurations (Fig. 14) cholestenes, derived by elimination reactions, are... 

Preparation of enolphosphates. The reagent is used in ether solution to convert A4-cholestene-3-one (I) into the enol form for reaction with diethyl phosphoro-chloridatc and tricthylamine to give the phosphate ester (3). Reaction with lithium and ethylamine, and treatment with t-butyl alcohol then affords 5-methyl-A -coprostene (4). 

Alcchols - iodides. Aliphatic primary and secondary alcohols react with (1) in THF, benzene, or hexane at 35-50° to give the corresponding iodides, usually in high yield. Even sierically hindered alcohols react, although in somewhat low yields. The reaction proceeds with inversion thus 3j5-cholestanol is converted into 3 -iodocholes-tane in 84% yield. Cholesterol is converted into the previously unknown 3a-iodo-A -cholestene (40% yield). 

Reactions with steroidal monoolefms Photooxygenation of A -3-methyl-5a-cholestene (1) with hcmatoporphyrin as sensitizer, followed by reduction of the initially formed hydroperoxides with methanolic sodium iodide, gives the two allylic alcohols (2) and (3). Similar oxidation of the isomeric A -2-methyl-5a -cholestene yields the... 

Maruoka has successfully developed a highly accelerated Oppenauer oxidation [31,32] system using a bidentate aluminum catalyst [29]. This modified, catalytic system effectively oxidizes a variety of secondary alcohols to the corresponding ketones as shown in Sch. 9. For example, reaction of (2,7-dimethyl-l,8-biphenylene-dioxy)bis(dimethylaluminum) (8, 5 moI%) with carveol (14) at room temperature in the presence of 4-A molecular sieves, and subsequent treatment with pivalaldehyde (3 equiv.) at room temperature for 5 h yielded carvone (15) in 91 % yield. Under these oxidation conditions, cholesterol (16) was converted to 4-cholesten-3-one (17) in 75 % yield (91 % yield with 5 equiv. t-BuCHO). 

Methylsterols (4-desmethyl triterpenes) and sterols (4,4-di-desmethyl triterpenes) present in olive oils are derived from the tetracyclic alcohols. The following methyl sterols (4a-methyl-7-cholesten-3p-ol compounds) are present 24-methylene, 24-methyl-, 24-ethylidene, and 24-ethyl. 

Synonyms ( — )-Cholesterol 5,6-Cholesten-3)S-ol 5-Cholesten-3/l-ol Cholest-5-en-3 S-ol Cholester-in Cholesterine Cholesterol base H Cholesteryl alcohol Cordulan D [5](-Cholesten-3 S-ol) Duso-line Dusoran Dythol S-Hydroxycholest-5-ene Hydrocerin Kathro Lanol Nimco Nimco cholesterol base No. 712 Provitamin D Super hart-olan Tegolan... 

Thus secondary or tertiary alcohols ROH can be reduced to RH via their thiocarboxy-lates R C(S)OR, or dithiocarbonates [xanthates, R S(CS)OR the Barton McCombie reaction] 147-149 for example cholesteryl thiobenzoate or S-methyl dithiocarbonate gives cholest-5-ene in 90% and 78% yield respectively (equation 15-47, R = Ph or MeS). The reaction works best for secondary alcohols the 0-t-alkyl xanthates are often rather unstable at room temperature, though the reactions can be carried out at low temperature with initiation by Et3B/02. The primary alkyl xanthates undergo C-O fission only at higher temperatures, when other reactions may compete. The thiocarbonyl imidazolides provide a variant on this theme, and the cholesterol derivative (15-5, R = /V-imidazolc) reacts with tributyltin hydride to give an 18% yield of cholestene.147... 

A4 -Cholestcne-3-one, 269 As-Cholestene-3-one, 380 A4-Cholestenyl acetate, 265 A9( 1 )-Cholestenylacetate, 265 Cholesteryl acetate, 51 Cholesteryl phosphorodichtoridate, 390 Cholic add, 252,416 Chromic acid, 95-96 Chromic anhydride, 96-97 Chromic anhydride in graphite, 97 Chromic anhydride-Pyridine, 96, 304 Chromium(II)-amine complexes, 97 Chromium(lll) chloride, 162 Chromium hexacarbonyl, 346 Ouomium(II) perchlorate, 97 Chromous acetate, 97-98 Chromous chloride, 506 Chromyl chloride, 98-99 Qnnamaldehyde, 97,269,406 Cinnamic alcohol, 97 Cinnamyl acetate, 322... 

Epoxides. A synthetic sequence which has been of particular value in the steroid field consists in conversion of an olefin into the epoxide and reductive fission to one of the two possible alcohols. A -Cholestene (1) gives the la,2a-epoxide (2) and this CH, I CHd CHa... 

Acetates of a-ketols or their vinylogs are subject to reductive elimination of the acetoxy group by treatment with zinc dust and acetic acid. Thus both 6a- and 6/3-acetoxy-A -cholestene-3-one (16) are reduced smoothly to A -cholestene-B-one (17) the free alcohols are reduced somewhat less smoothly." In the case of steroidal... 

In view of the above preference, it is perhaps unsurprising that equatorial attack on these substrates can be quite hard to achieve. Thus, 4-cholesten-3-one was treated with a range of hydrides with the intention of finding a method for formation of the axial alcohol, 4-cholesten-3a-ol. Both L- and K-Selectride gave preferentially the equatorial product, and even LS-Selec-tride gave only a 1 1 mixture of the two isomers1 IS. 

Oxidation of these n-allylpaUadium complexes proceeds regio- and stereo-selectively to ally lie alcohols. Thus treatment of (2) in pyridine (1 eq.) with m-chloroperbenzoic acid in petroleum ether gives 4a-hydroxy-A -cholestene the -isomer (3) is oxidized to 6/3-hydroxy-A -cholestene. The oxidation of (4) to 7a-hydroxy-A -cholestene is even more selective. Oxidation in the absence... 

Cholesterol (koh-LESS-ter-ol) is also known as cholesterin cholest-5- - - 5-cholestin-3-P-ol 3P-hydroxy-5-cholestene and io,i3-dimethyl-i7-(6-methylheptan-2-yl)-2,3,4,7,8,9,n,i2,i4, i5,i6,i7-dodecahydro-iH-cyclopenta[a]phenanthren-3-ol. It is a waxy white or pale yellow solid with virtually no taste or odor. It is present in the bodies of all higher animals, especially in the brain and spinal cord. Chemically, cholesterol is classified as a fat, a member of the lipid family. Fats are the product of the trihydric alcohol (alcohol with three -OH groups) glycerol and a fatty acid. Fatty acids are organic acids with many carbon atoms, usually eight or more. 

CAS 57-88-5 EINECS/ELINCS 200-353-2 Synonyms Cholest-5-en-3p-ol 5-Cholesten-3-p-ol Cholesteric esters Cholesterin Cholesteryl alcohol... 

Ergosterol, E-00058 Ergosterol D, in M-00018 Ergosterol Bj, in M-00017 Erucic acid, in D-00207 A -Erucoyl-4-sphingenine, in D-00210 Erucyl alcohol, in D-00209 Erythrogenic acid, see 0-00149 3/3-Ethoxy-5-cholestene, in C-00026... 

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