5a-Cholestane-3,7-dione

Selenium dioxide (SeOa) in tert-alcohols has been widely used for the dehydrogenation of 3-0x0 steroids, and particularly in the conversion of A -3-ketones into A dienones [240]. Other steroidal ketones suffer similar a,jS -dehydrogena-tion e.g. i2-ketones [241] and a 4,4-dimethyl-7-ketone [242]), but the same reagent in different solvents will also effect oxidation of certain steroidal ketones with adjacent methylene groups ( C0-CH2 ) into a -diketones (-CO CO-), a reaction which is common outside the steroid field. In ethanolic solution, for example, 5a-cholestan-3 one was oxidised by SeOa to give 5a-cholestane-2,3-dione [243], isolated in its enoHc forms. 

Cholestane-3/3,5a-diol 3-acetate, 397 Cholestane-4a,5a-diol 4-tosylate, 398 Cholestane-5a,6a-diol 6-tosylate,394 5a-Cholestan-2-one, 57, 88, 427 10(5 4 H)ijAeo-Cholestan-5-one, 398 10(5 6)ij ieo-Cholestan-5-one, 392, 394 5a-Cholestan-3-one cyanohydrin, 359 5a-Cholestan-3-one cyanohydrin acetate, 360 5a-Cholestan-2a,3a-oxide, 42 5a-Cholestan-2/3,3/3-thiirane, 43 Cholest-5-ene-3, 19-diol, 268 Cholest-5-ene-3, 25-diol, 71 5(10->l/3H)flfc eo-cholest- 10(19)-ene-3/8,5a-diol 3-acetate, 397, 398 Cholest-4-ene-3,6-dione, 105 Cholest-4-en-3-one, 318 Chromium trioxide, 147, 150 5a-Conanine-3/3-ol-ll-one 3-acetate, 259 Cupric bromide, 210, 211 Cuprous chloride-catalyzed conjugate addition, 76, 80... 

Cholestane-2a,3 -diot dibenzoate, 1008 aiolestane-2/3,3a-diol dibenzoate, 1008 Cholestane-3/S,7,S-diol 3,7-dicathylate, 366 Cholestane-3/3,4(5-diol 5a,6a-epoxide, 796 Cholestane-3d,7a-diol 3-monocathylate, 366 Cholestane-4a,5a-diol-3-one, 476 Cholestane-4/3,5/3-diol-3-one, 476 Cholestane-4a,5ii-diol 4-tosylate, 103, 104 Cholestane-5a,6a-diol 6-tosylate, 103,104 Cholestane-2,3-dione, 304, 962 enols of, 747... 

Hecogenin p-toluenesulfonylhydrazone, 402 Hofmann-Loffler reaction, 257 Homoallylic rearrangements, 379 A-homo-5a-cholestan-3-one, 356, 358, 362 A-homo-5a-cholestan-4-one, 359, 360, 368 A-homo-choIest-4a-en-3-one, 366 A-homo-estra-1(10), 2,4a-triene-4,17-dione, 367,370... 

Better yields of cyclobutanones were obtained with steroidal ketones.85 86 In the reaction of 5a-cholestan-3-one (5) with diazocyclopropane, spiroannulation to give 6 (30%) dominated insertion to give 7 (24%), and with 3/ -acetoxy-5a-pregnane-l 1,20-dione (8) only spiroannulation to give 9 (60%) was observed.85 A comparable high yield (78%) of a spiroannulation product 11 was obtained with trispiro[2.0.2.0.2.1]decan-10-one (10).84 It is apparent that efficient formation of oxaspiropentanes as direct precursors of cyclobutanones only takes place with sterically hindered ketones. 

Methylthiotrimethylsilane converts aldehydes and ketones into bis(methyl-thio)acetals under very mild conditions, without the need for an acidic catalyst. 5a-Androstane-3,17-dione reacted selectively at C-3.The reaction appears to depend upon the high affinity of silicon for oxygen.2-Methylenepropane-l,3-diol protects ketones as acetals from which the ketones can be regenerated without resort to acidic treatment, if required.Hypophosphorous acid adds on to 3-oxo-steroids to give 3-yl phosphonous acids. 5a-Cholestan-3-one gives the 3-hydroxy-derivative (177), but a 4-en-3-one gives the 3,5-dien-3-yl phosphonous acid (178). ... 

Reduction of enediones. A4-Cholestene-3,6-dione (1) is reduced by chromous chloride in either THF or acetone to 5/3-cholestanone-3,6-dione (2).3 Note that reduction with zinc and acetic acid gives the more stable 5a-cholestane-3,6-... 

The primary amino group of (22, 2S5)-26-amino-5a-cholestane-3, 16, 22-triol was acetylated by N. restrictus [244). Side-chain-cleaving enzymes, induced by cholesterol in Arthrobacter simplex, are reported to be capable of splitting the spiroaminoketal side chain of tomatidine (9). Yields of 2.S%-4.0% of androsta-1,4-diene-3,17-dione were obtained in the presmce of a,ot -dipyridyl [245). Tomatidine (9), iV-acetyltomatidhie, soladulddine (161), and (22/ ,255)-22,26-epimino-5a-cholestane-3, 16/ -diol were transformed by N. restrictus into the corresponding 3a-hydroxy compounds [246). 

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