Photochemical reactions. 141 st communication. Photochemistry of α,β‐unsaturated δ,ϵ‐epoxyketones of the ionone series

On n,π*‐ as well as on π,π*‐excitation, the 4,5‐epoxy‐α‐ionones ( E )‐ 1 , ( E )‐ 2 , and ( E )‐ 3 undergo ( E )/( Z )‐isomerization and subsequent γ‐H‐abstraction leading to the corresponding 4‐hydroxy‐β‐ionones ( E / Z )‐ 9 , ( E / Z )‐ 13 , and ( E / Z )‐ 17 as primary photoproducts. On photolysis of ( E )‐ 3 , as an additional primary photoproduct, the β,γ‐unsaturated σ,ϵ‐epoxy ketone 18 was obtained. The other isolated compounds, namely the 2 H ‐pyrans 10A + B and 14A + B as well as the retro γ‐ionones 11 and 15A + B , represent known types of products, which are derived from the 4‐hydroxy‐β‐ionones ( E / Z )‐ 9 and ( E / Z )‐ 13 , respectively.