Photochemische Reaktionen 122. Mitteilung [1]. Zur vinylogen β-spaltung von epoxy-enonen: Photoisomerisierung des 3,4:5,6-diepoxy-5,6-dihydro-β-jonons

✍ Scribed by Norbert Bischofberger; Guy De Weck; Bruno Frei; Hans Richard Wolf; Oskar Jeger

• Publisher: John Wiley and Sons
• Year: 1981
• Tongue: German
• Weight: 716 KB
• Volume: 64
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19810640606

✦ Synopsis

Vinylogous β‐Cleavage of Epoxy‐enones: Photoisomerization of 3,4: 5,6‐Diepoxy‐5,6‐dihydro‐β‐ionone

On ^1^n,π*‐excitation (λ>347 nm), 3,4:5,6‐diepoxy‐5,6‐dihydro‐β‐ionone ((E)‐3) shows the typical behaviour of α,β‐unsaturated γ,δ‐epoxy ketones furnishing the (Z)‐enone 3 and by C(γ),O cleavage of the oxirane the dihydrofuryl ketone 10 and the cyclohexanones (E/Z)‐11. However, on ^1^π,π*‐excitation an unexpected type of transformation is observed: (E)‐3 is isomerized to the four aliphatic triketones 5–8 as the main products. To a smaller extent the allene diketone 9 is formed by a known type of isomerization as well as (Z)‐3.

As the starting material for the preparation of (E)‐3, the known epidioxy‐enone (E)‐4 was used. In addition to (E)‐3, (E)‐4 gives the aliphatic triketone 6 and the hydroxyenone 15 by thermal or catalytic isomerization.