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 proton transfer

摘要: Irradiation of 5β-cholest-1-en-3-one oxime 14 in methanol gave 1α-methoxy-5β-cholestan-3-one 16, arising from the photoaddition to double bond enone oxime. 1α-Methoxy-5β-cholestan-3-one 17 as well 10β-methoxy-5(10→1)abeo-1β(H),5β,10α(Me)-cholestan-3-one 15, a skeletal rearrangement (generated oxime), were accompanying products this photoreaction. Deuterium-labelling studies confirmed that formation 1α-methoxy-5β-cholestan-3-oxime 16 involves stereospecific syn addition photogenerated, twisted, ground-state oximes B rear side steroidal framework.Irradiation 1-methyl-5β-cholest-1-en-3-one 23 methanol, on other hand, almost exclusively 1-methylene-5β-cholestan-3-one 24, photodeconjugation α,β-double β,γ-position. A deuterium-labelling study established deuterium is stereospecifically introduced at 2β-position methanol[2H]ol while 2α-position its 5α-isomer 6. These results are fully consistent with our previously proposed pathway concerning 1-methyl-5α-cholest-1-en-3-one 6; proton twisted D framework was followed by loss 1-methyl group resulting carbocation intermediate. Neither isoxazole derivative, product photoreaction 5α-cholest-1-en-3-one 1, nor unsaturated lactam photo-Beckmann formed photoreactions either or derivative 23.