As-Cholestene

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,... 

Muzart and coworkers investigated the CrOs/TBHP catalyzed oxidation of various benzylic methylenes and the allylic oxidation of A - and A -cholesten-3-one to the corresponding ketones in CH2Cl2 as well as benzotrifluoride (BTF) as solvent (Scheme 130) °. It could be shown that BTF in most cases improved the results even though the reactions were carried out with less TBHP than in CH2CI2 (4 eq. compared to 7 eq.). Yields in CH2CI2 varied from 21 to 94% and those in BTF from 40 to 99%. 

S-Chlorovinyl methyl ketone, 32, 29 3,4-reco-A -CHOLESTEN-3,4-Dioic Aan, 35, 38... 

Etherification, When cholesterol (1) is heated for several hours in dimethyl phosphite, cholesteryl methyl phosphite (2) is obtained as the main product. However, if/>-TsOH is present, 3/S-mcihoxy-A -cholestene (3) is obtained as the main product in about 60 % yield. Cholestanol is converted by this method into 3/S-methoxycholestanc in 60-70% yield. 

For reaction with A -cholestene, iodine thiocyanate was prepared in methylene chloride 2, 3 -cpithiocholestane was obtained in 46% yield. 

Disubstituted steroid olefins are converted by the reagent into a-azido ketones. Thus A -cholestene (9) reacts with the reagent in dichloromethane at —20° to give 3a-azidocholestanone-2 (10) in 50-60% yield. A possible mechanism is formulated. The... 

Oxidation of steroidal alketies. Mercuric acetate (2 eq.) reacts with A -steroids (I) to give as the major product A -15-ones (2) rather than the expected allylic acetates, 16(J-acetoxy-14-enes. The tetrasubstituted bond of A -cholestene is unreactive under the same conditions. A -Cholestene (disubstituted) reacts only slowly to give A -cholestene-3-one in 20 % yield with 70% recovery of the starting material. This unexpected reaction of steroidal trisubstiluted double bonds may proceed through an allylic acetoxylation followed by an oxidation step. 

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). 

Complete retention of configuration is observed in the reaction of 3/ ethoxy-A -cholestene with acetyl chloride 3/J-chloro-A -cholestene is formed in high yield, accompanied by a small amount of A - -cholestadiene. 

The reaction has been used to convert A -cholcstenone-3 into 3-methylcne-A -cholestene in about 40% yield. Reaction of A -cholestenone-3 with mcthylenetri-phcnylphosphorane gives impure 3-methylcne-A -cholestenc in < 15% yield. 

Presence of phytosterols in oat oil was first reported by Idler et al. in 1953 (128). Oat grain contains 35-60 mg phytosterols/100 g grain (127). Phytosterol content of oat oil varies between 0.19% to 0.32% (125). p-Sitosterol (40-70% of total sterols) is the major phytosterol in oats. A - and A -Avenasterol are the two other phytosterols that present in significant quantities in oats. Campesterol, stigmasterol, A -stigmasten-3p-ol, A -cholesten-3p-ol, and cholesterol were also present in oat grain. 

In the electrolysis of the A -cholestene-3)5-carboxylic acid (71) three products were identified. The product containing a cyclopropyl ring (73), is possibly formed via the bridged cationic intermediate (72). 

The above ketone methylenation is applicable to highly hindered ketones, which are usually inert to the Wittig method. For example, a highly hindered tricyclic ketone (norzizanone, 4a) undergoes the methylenylation to give zizaene (4b equation 4). A -Cholesten-3-one (5a) was also converted to the nonconjugated diene 3-methylene-A -cholestene (5b equation 5). ... 

Acetoxy-A -cholestene-7-one, 526 Acetoxycyclooctatetraene, 401 Acetoxymercuri-7 -acetoxybicy clo [3.2.1]-octene-2, 319... 

A Fannitalia group" reported, without details or yields, that both the a- and j3-epoxides derived from testosterone are rearranged by BFs-etherate in benzene to 4-hydroxy-A -3-ketones. Collins (Australia) made a more detailed study in the cholestane series and found that both the a- and the fi-oxide indeed give the hydroxy-A -cholestene-3-one but that they both yield a second product characterized as 5/8-A-norchoIestane-3-one. TTie latter compound evidently comes from an intermediate /3-keto aldehyde, probably by deformylation during chromatography on neutral alumina. 

A preliminary report" states that reaction of cholesteryl benzoate with (-butyl hydroperoxide and a catalytic amount of cuprous bromide in benzene gave equal parts of A -cholestene-3, 7a- and -3, 7j8-diol dibenzoate. Here allylic attack is not attended with rearrangement. 

Exhaustive dichromate oxidation of cholesterol and removal of an extensive acidic fraction leaves a mixture of A -cholestene-3,6-dione and several monoketones and other neutral products. Repeated extraction of a solution in petroleum ether with... 

Cupric nitrate-Pyridlne. This complex in the presence of triethylamine as base catalyzes the reaction of A -cholestene-3-one with molecular oxygen to form A -cholestene-3,6-dione. The yield is about twice that (4>tained by dichromateoxidation. ... 

Both simple carbonyl compounds and a,j8-unsaturated ketones react with this reagent with exclusive formation of epoxides (oxiranes), not cyclopropanes. Yields are as follows benzaldehyde, 75% cycloheptanone, 97% benzalacetophenone, 87% carvone, 89% eucarvone, 93% pulegone, 90% A -cholestene-3-one, 90%. 

Abnormal products have been encountered in the BF -catalyzed condensation of ethanedithiol with steroid ketones. For example, A -cholestene-3/3-ol-6-one acetate (4) on treatment with excess ethanedithiol (BFg-AcOH) gave the C4-epimers (5) and (6). 

Oxidation of A -cholestene-3-one in ether solution with 30% hydrogen peroxide and a catalytic amount of OSO4 gives both possible ei.s diols, which were isolated in the yields indicated. ... 

Generation. By the reaction of an aqueous suspension of silver azide and an ethereal solution of iodine. Hantzsch obtained the reagent us an unstable solid. Hassner and Levy generated the pseudohulogen more conveniently from iodine monochloride and sodium azide in DMF or acetonitrile solution and found that it adds stereospecifically to olefins. Thus A -cholestene is converted info the tran.%-diaxiul 2/I-azido-.la-iadocholesliine. Yields of adducts fh>m cyclohexenc, styrene, W.v- and trnn.v-stllbene were HO, 70, fi.I, and 80%. 

A -Cholestene-3-one (1) has a highly reactive methylene group and is oxidized by lead tetraacetate in benzene-acetic acid to give the 4a-acetoxy derivative (2)... 

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