9,10-Cyclo steroids

The displacement of homoallylic tosylates follows an entirely different course with a strong tendency for the formation of cyclo steroids. Thus, when the 3/ -tosylate of a A -steroid (187) is treated with lithium aluminum deuteride, the product consists mainly of a 3l3-di-A -steroid (188) and a 6c-dj-3,5a-cyclo steroid (189). The incorporation of deuterium at the 3 -position in (188) indicates that this reaction proceeds via a 3,5-cyclo cholesteryl cation instead of the usual S, 2 type displacement sequence. This is further substantiated by the formation of the cyclo steroid (189) in which the deuterium at C-6 is probably in the p configuration. ... 

The synthesis of epoxides proceeds in the presence of a variety of functional groups and is also applicable to cyclo steroids. Halo epoxides, e.g, (45), can... 

The lla-hydroxy-11,19-cyclo steroids are very efficiently converted into 19-acetoxy-11-ketones by treatment with lead tetraacetate in benzene. ... 

Lead tetraacetate fragmentation has not been applied to the 20-hydroxy-18, 20-cyclo steroids. However, preferential cleavage of the 17,20-bond would be expected, as was observed in the chromic acid oxidation of a saturated 20-hydroxy-18,20-cyclo steroid in hot acetic acid which affords the 18-acetyl-17-ketone in 50-60% yield. 

Hydrolysis of 6p,l9-Oxido-3a,5a-cyclo steroids.A solution of 0.1 g of 3a,5a-cyclo-6)5,19-oxidocholestane in 20 ml of acetone is treated with 1.0 ml of water and 0.5 ml of 1 N sulfuric acid. After standing for 2 hr at room temperature, the solution is neutralized with saturated sodium bicarbonate solution and extracted with ether. The combined ether extracts are washed with water and concentrated to dryness under reduced pressure. Recrystallization of the crude product from methanol yields 85 mg choIest-5-ene-3, 19-diol mp 147-149° [aj —30°. 

Recent work by Syhora, Edwards and Cross " has confirmed the p-orientation of the substituent introduced at C-6 in 5, 19-cyclo steroid (69) in the kinetically controlled hydrolysis of A -19-methanesulfonoxy steroids. 

An unusual reaction leading to a 5a,9a-cyclo-steroid (15) occurred when the ii -acetoxy-ga-bromo compound 16) was reduced with chromous ions [y4]. The mechanism of chromous ion reduction of halides has already been mentioned (p. 53). In the present case the pa-chromium complex (17) or its... 

Intramolecular radical capture was observed when a 19-CH2 radical (17) was generated by irradiation of corticosterone 21-acetate ii nitrite (16 [14]. In addition to the i8-oxime (20 21% yield), the 4-oximinO 5j5,19-cyclo-steroids (19 two oxime isomers) were major products (45%). These arose through sr-electron attack on the 19-CH2 radical to form the... 

If 3jS tosyloxy-As steroids are solvolysed in weakly basic buffered media e.g. potassium acetate in aqueous acetone or in methanol) under mild conditions, the usual products are 6 substituted 3,5-cyclo-steroids (3), commonly referred to as "i-steroids . These are derived by nucleophilic attack of solvent or an anion upon the 6/5-position in the mesomeric cation 2). The theoretical significance and practical utility of this reaction have been studied intensively since its discovery by Stoll in 1932, and the present survey collects results of mechanistic importance from some eighty papers bearing on the subject. 

The Ritter reaction (with a nitrile and acid) converts either a 6j3-hydroxy-3a,5a-cyclo-steroid or a 3jS-mesyloxy-A -steroid into the 3/ -acylamino-A -derivative... 

The stereospecific synthesis of (20S,22R)-17a,20,22-trihydroxycholesterol (388) and its (20S,22S)-isomer (389) has been reported. Addition of vinyl Grignard reagent to the known 16a.l7a-oxidopregnenolone acetate (385), followed by opening of the epoxide with lithium aluminium hydride, furnished the 17,20-dihydroxy-intermediate (386). Conversion into the 3,5-cyclo-steroid (387) and epoxidation of the remaining double bond afforded a C-22 epimeric mixture of epoxides which, on reaction with s-butyl-lithium and reconversion into the 3jS-hydroxy-A -steroids, afforded the epimeric tetraols (388) and (389). The preparation of similar 3,17,20-triols is also reported. ... 

P Toluenesulfonic acid 3) -Sulfonio- from 3,5>cyclo-steroids... 

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