- Tetramethyldiamidophosphoric acid chloride mediated epoxide-diene conversion and steroidal aromatization
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The reaction of tetramethyldiamidophosphoric acid chloride with epoxides in the presence of a trace amount of water furnished 1,3-dienes in good yield. The conversion works with open chain and cyclic epoxides. A C-C bond cleavage reaction occurs if the epoxide contains a quaternary carbon. Application of this method to epoxy sterols afforded ring A aromatic steroids in good yield. The aromatization works via dienol-benzene rearrangements and is independent of the C-3 stereochemistry.
- Demir, Ayhan S
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p. 227 - 233
(2007/10/03)
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- Unexpected Cyclisation of an Acetylenic Acetal: Vinyl Cation Capture by Internally transferred Hydride
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The acetylenic acetal (2) is converted in 90 percent yield to a mixture of cholesta-3,5- and 4,6-dienes on reflux in toluene containing toluene-p-sulphonic acid.
- Keirs, David,Overton, Karl,Thakker, Krishan
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p. 310 - 311
(2007/10/02)
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- Synthesis of Cholestenothiazoles and Cholestanooxazolidine
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4β,5-Epoxy-5β-cholestan-3-one (I) reacts with thiourea to afford 5β-hydroxycholest-3-eno-2'-aminothiazole (II) while with thiacetamide it furnishes 3,5-cholestadieno-2'-methylthiazole (III) and 5β-hydroxycholest-3-eno-2'-methylthiazole (IV). 6β-Chloro-5-hydroxy-5α-cholestane (V) on treatment with KSCN in dimethylformamide gives cholesta-4,6-diene (VI), 5α-chloestan-6-one (VII), 5-hydroxy-5α-cholestan-6α-yl isothiocyanate (VIII), 5-hydroxy-5α-cholestan-6-one (IX) and 5α-cholestano-2'-thiooxooxazolidine (X).The structures of these compounds have been established on the basis of spectral properties, analytical data and also by direct comparison with authentic samples where available.
- Ahmad, M. S.,Alam, Zafar
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p. 486 - 488
(2007/10/02)
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- Reactions of steroidal 5,6-epoxides and cyclohexene oxide with aluminum alkoxides
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The isomeric 5,6α- and 5,6β-epoxycholestanes, in addition to an analogous series of compounds substituted at C-3 with hydroxy (α or β stereochemistry) or ethylene ketal groups, have been treated with aluminum isopropoxide or tert-butoxide.The latter series of reactions did not give identifiable material, but aluminum isopropoxide gave products derived from epoxide opening and rearrangement in all cases.With epoxides unsubstituted at C-3, aluminum isopropoxide functioned as a Lewis acid in promoting epoxide rearrangements.In the presence of a C-3 alcohol function, additional products were obtained arising from fragmentation of the C-4,C-5 bond, or from β-elimination of the epoxide involving the loss of a C-7 hydrogen.Meerwein-Pondorff reduction of product carbonyl groups was also observed.C-3 ketal substituted epoxides were rearranged cleanly to 6-hydroxy-Δ4-3-ketones.Cyclohexene oxide reacted with aluminum isopropoxide (but not with tert-butoxide) to give two products arising from epoxide addition reactions.Structures for these products are proposed based on their 13C nmr spectra, and a possible route for their formation is presented.None of the epoxides examined in this study reacted with magnesium methoxide.
- Holland, Herbert L.,Khan, Saeed R.
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p. 2763 - 2768
(2007/10/02)
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