Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Photolysis of (E)-5-Isopropyl-6-methyl-5,6-epoxy-hept-3-en-2-on.This paper continues the series of investigations of the photochemistry of α, β-unsaturated γ, δ-epoxy-ketones, by examinating the photochemical behaviour of the aliphatic vinylogous epoxy-ketone 1, the chromophore of which is structurally similar to that of γ, δ-epoxy-(E),β-ionone (44).On π, π*-excitation (λ = 254 nm) 1 isomerizes mainly to the enol-ether 2 and gives as minor products the isomeric dihydrofurane 3, the 1,5-diketones 4 and 5 and the 1,3-diketone 6. To a smaller extent, 1 also undergoes photofragmentation to the furane 7, the allenyl-ketone 8 and the cyclopropenyl-ketone 9. On n,π*-excitation (λ ≥ = 347 nm) 1 yields the photoisomers 3, 4, 5 and in traces the hydroxyallenyl-ketone 14, but no fragmentation products. It is shown that on irradiation at λ ≥ = 254 nm the 1,5-diketone 4 isomerizes to 5, 6 and 15 and photodecarbonylates to the β, γ-unsaturated ketone 16.The isomers 3, 4 and 5, obtained both from n, π*- and π,π*-excitation, represent products of cleavage of the C(γ)—O-bond in 1. The enolether 2, on the other hand, formed only by π,π*-excitation, results from cleavage of the C(γ)—C(δ)-bond.Finally, the fragmentation products 7, 8 and 9, which could be detected only on π,π*-excitation, may arise from a common intermediate g ↔ h.
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