PHOTOCHEMISCHE REAKTIONEN

Article abstract of DOI:10.1002/hlca.19800630305

On ¹n,?^*-excitation (λ>347 nm) citral (5) and the methyl ketone 10 isomerize to compounds A (7, 19) and B(6, 20), whereas the phenyl ketone 11 changes into the isomer 24 of type E. evidence is given that the conversion to A and B may arise from the ³n,?^*-state of the 2,6-diene-carbonyl compounds.On ¹p,?^*-excitation (λ=254 nm) 5 and 10 yield the isomers A (7, 19) and D (18, 22), but no products of type B.Futhermore, conversion of 10 to the isomer 21 of type C is observed.Selective ¹?,?^*-excitation (λ=254 nm) as well as selective ¹n,?^*-excitation (λ>347 nm) of the 2,7-diene-carbonyl compounds 12 and 13 give rise to isomerization to the compounds F (25, 28), exclusively.The intramolecular (2+2)-photocycloadditions are shown to be triplet processes.UV.-irradiation (λ>280 nm) of compounds F (25, 28) furnishes the isomeric products G (26, 29) which photoisomerize to oxetanes of type H (27, 30).