- Photoinduced Molecular Transformations. Part 134. Photoinduced Stereospecific Addition of Methanol to 5β-Cholest-1-en-3-one Oxime and Photoinduced Deconjugation of its 1-Methyl Derivative involving Stereospecific Electron Transfer
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Irradiation of 5β-cholest-1-en-3-one oxime 14 in methanol gave 1α-methoxy-5β-cholestan-3-one oxime 16, arising from the photoaddition of methanol to the double bond of the enone oxime. 1α-Methoxy-5β-cholestan-3-one 17 as well as 10β-methoxy-5(10->1)abeo-1β(H),5β,10α(Me)-cholestan-3-one 15, arising from a skeletal rearrangement of 5β-cholest-1-en-3-one (generated from the oxime), were the accompanying products in this photoreaction.Deuterium-labelling studies confirmed that the formation of 1α-methoxy-5β-cholestan-3-oxime 16 involves a stereospecific syn addition of methanol to the photogenerated, twisted, ground-state double bond of the oximes B from the rear side of the steroidal framework.Irradiation of 1-methyl-5β-cholest-1-en-3-one oxime 23 in methanol, on the other hand, gave almost exclusively 1-methylene-5β-cholestan-3-one oxime 24, arising from photodeconjugation of the α,β-double bond to the β,γ-position.A deuterium-labelling study established that deuterium is stereospecifically introduced at the 2β-position of 1-methyl-5β-cholest-1-en-3-one oxime 23 in the photodeconjugation in methan2H>ol while deuterium is stereospecifically introduced at the 2α-position in the photodeconjugation of its 5α-isomer 6.These results are fully consistent with our previously proposed pathway concerning the photodeconjugation of 1-methyl-5α-cholest-1-en-3-one oxime 6; the stereospecific addition of a proton to the photogenerated, twisted double bond of the oxime D from the rear side of the steroidal framework was followed by the loss of a proton from the 1-methyl group of the resulting carbocation intermediate.Neither the isoxazole derivative, a product in the photoreaction of5α-cholest-1-en-3-one oxime 1, nor the unsaturated lactam from a photo-Beckmann rearrangement was formed in the photoreactions of either 5β-cholest-1-en-3-one oxime 14 or its 1-methyl derivative 23.
- Suginome, Hiroshi,Nagaoka, Atsushi,Senboku, Hisanori
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p. 3103 - 3110
(2007/10/02)
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