Showing papers on "Enone published in 1968"
TL;DR: In this article, the α,β-unsaturated γ,δ-epoxyketone 7 is isomerized almost exclusively to the δ-diketone 9 both upon irradiation in the n π* absorption band with light of wavelengths above 310 nm (in anhydrous dioxane or benzene solutions) and upon triplet sensitization using acetophenone in benzene.
Abstract: The α,β-unsaturated γ,δ-epoxyketone 7 is isomerized almost exclusively to the δ-diketone 9 both upon irradiation in the n π* absorption band with light of wavelengths above 310 nm (in anhydrous dioxane or benzene solutions) and upon triplet sensitization using acetophenone in benzene. The reaction may be formulated by the cleavage of the CγO oxide bond and the shift of the δ-hydrogen to the γ-position, and thus bears a formal “double bond homology” to the photochemical α,β-epoxyketone rearrangement.
Excitation in the π π* absorption band of 7 with light of wavelength 253,7 nm (in anhydrous dioxane solution) leads to the formation of product 10 as well as to the triplet rearrangement to 9. With this result a novel partial synthesis of O-acetyl-B-nortestosterone has been accomplished, which has the advantages of fewer steps and higher product yield (7 10: ∼30% yield) than previously published syntheses. On the basis of the presently available experiments, the mechanism of the transformation 7 10, which constitutes one of the still few examples of enone photoreactions induced selectively from the π,π* excited singlet, remains unknown.
27 citations
19 citations
TL;DR: The action of chromium trioxide under acidic conditions on axial allylic alcohols has been studied in this article, where it was shown that the reaction can lead to transoid enones.
Abstract: The action of chromium trioxide under acidic conditions on steroid allylic alcohols has been studied. Whereas the equatorial isomers are always oxidised to the corresponding enones, the axial counterparts can undergo either a similar oxidation to the enone or epoxidation of the double bond and oxidation of the alcohol, to lead ultimately to an epoxy-ketone.With the axial allylic alcohols in which the rate of oxidation of the secondary alcohol is faster than that of epoxidation of the double bond, enones will be formed, whereas with those in which the relative rates of these two processes are reversed epoxy-ketones will be produced. Usually unsaturated alcohols which yield transoid enones belong to the first group, whereas those which would result in cisoid enones are of the second.Whenever a compound first undergoes an allylic rearrangement, the stereochemistry of the product determines the fate of the reaction with chromium trioxide.Epoxidation of the double bond in axial allylic alcohols is stereospecific and takes place always on the same side of the molecule as the hydroxy-group; it proceeds presumably through formation of a chromate ester followed by the transfer of an oxygen atom to the double bond.
7 citations
TL;DR: The spontaneous and base-catalysed isomerization of 1-tosylazocyclohexene to yield cyclohex-2-enone tosylhydrazone has been studied in benzene, dioxan, chlorobenzene, and anisole as mentioned in this paper.
Abstract: The spontaneous and base-catalysed isomerization of 1-tosylazocyclohexene to yield cyclohex-2-enone tosylhydrazone has been studied in benzene, dioxan, chlorobenzene, and anisole. In benzene solution, the effectiveness of tertiary amines in catalysing the reaction is roughly proportional to their pKa measured in water, and related to a consistent decrease in the activation energy. The catalytic activity of triethylamine is solvent-dependent and increases in the order: benzene < dioxan < chlorobenzene < anisole. The uncatalysed reaction is, however, only slightly sensitive to solvent changes. For the base-catalysed reaction, a mechanism is suggested, involving the release of one allylic proton from the cyclohexene ring in a slow step.
5 citations