Photochemical reactions. 132nd communication. Photochemistry of 5,6-epoxy-5,6-dihydro-7-methyl-β-ionine: Influence of a methyl group at the enone side chain on the oxirane cleavage

¹n, π*-Excitation of the γ,δ-epoxy-enone (E)- 3 leads exclusively to the conformers (Z)- 3A + B . On ¹π, π*-excitation of (E)- 3 , in addition to (Z)- 3A + B , products 6–9 arising from a carbene intermediate e are formed. However, products of an isomerization via C(γ), O-bond cleavage of the oxirane were not formed on either mode of excitation. On thermolysis, at 80° the conformer (Z)- 3A is transformed into (Z)- 3B , which on photolysis returns to (Z)- 3A and (E) -3 . At 160°, however, (Z) -3B rearranges to the isomers 6, 10 and 11 .