3a,5-Cyclo-5a-cholestane

Base-catalysed autoxidation of either 3a,5-cyclo-5a-cholestan-6-one or 3a,5-cyclo-5a-cholestan-7-one gave the same products, which included the oxetanone (113). Similar oxidations of 2-oxo—steroids were reported, and of particular interest is the formation of the dioxide (115) from the 2,ll-dioxo-5/3-compound... 

For the discussion of the relationship between the sign of the (n, tc ) Cotton effect and molecular structure of spiran-type cyclopropyl ketones, such as 3a,5-cyclo-5a-cholestan-6 one (142), one must consider that the perturbing group comes into the near lower left (nil) octant. Then, the reversed octant rule predicts a negative sign for the (n, tc ) CE which is... 

Stereoelectronic control has been demonstrated in the j8-scission of 3a,5-cyclo-5a-cholestan-6-yl and 3j8,5-cyclo-5 8-cholestan-6-yl radicals, generated by irradiation of the corresponding 6j8-chloro-derivatives in the presence of PhaSnH and azobisisobutyronitrile. 

Reduction of 6P-methoxy 3aJ-cyclo-5a-steroids. Reduction of 6/ -methoxy-3ct,5-cyclocholestane (1) with mixed hydride affords as the major product 3a,5-cyclo-5a-cholestane (2). 

Interestingly, exactly the same selectivity was found in the reduction of 3a,5-cyclo-5a-cholestan-6-one. and 3) ,5-cyclo-5/ -cholestan-6-one (15) with lithium in liquid ammonia. This reduction probably proceeds via radical anion intermediates which have overlap factors analogous to the corresponding cyclocholestan-6-yl-radicals. The 3a,5a-oxo steroid gave 5a-cholestan-6-one (16) with high selectivity whereas 3, 5 -15 gave the reduced oxo steroid 17 which contains a five-membered A-ring. 

The reaction of 3a.5-cyclo-5a-cholestan-6 -yl acetic acid (6(X)) with H2SO4-HOAc gives 3-methyl-A-norcholest-3(5)-en-6/3-ylacetic acid (601), and not cholest-4-en-6/ -ylacetic acid, as reported in 1949. The reaction is therefore similar to that of unsubstituted 3a.5a-cyclosteroids (596). 

Photolysis of the oxime (684) of 3a,5-cyclo-5a-cholestan-6-one gave a very poor yield of ring b lactams,unlike the photo-Beckmann reactions of 5a- and 5j8-cholestan-6-one oximes, reported last year. ° The major products of photolysis of the 3a,5-cyclo-oxime were derived via initial conversion into the parent 6-ketone. ... 

Reaction of 3a.5-cyclo-5a-cholestan-6-one (359) with diazomethane made it possible to prepare a number of B-homo-keto-derivatives (360)—(364). Further homologation of the eight-membered-ring ketones (362), (363), and (364) led to the formation of the four ketones (365)—(368), in which a carbonyl group is contained in a nine-membered ring. ... 

A mixture of 3a,5-cyclo-5a-cholestane, mercuric acetate, and glacial acetic acid stirred and refluxed 1 hr. -> 3-hydroxymethyl-A-norcholest-3-ene acetate. Y 41%. E. C. Blossey, Steroids 14, 725 (1969). 

The stereochemical implications of the reductive opening of the cyclopropane ring in polycycles has been studied. The three-membered ring in the isomeric 3a,5-cyclo-5a- (24) and 3, 5-cyclo-5)S-cholestan-6-one (25) was opened differently. In the latter case, the cyclopropylmethylene group became a methyl group. The reduction of 4,5-methano-3-oxosteroids was shown to be stereospecific with respect to the orientation of the methyl group formed. ... 

A soln. of cyclo-3a,5a-cholestan-6/ -ol in acetic acid refluxed 5 min. in the presence of 30 parts alumina diolesteryl acetate. Y ca. 100%. A. Metayer and M. Barbier, Bl. 1972, 3625. 

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