AbstractThe title compounds (E/Z)‐7 were prepared in 66% overall yield by reaction of β‐ionone ((E)‐(1) with lithium dimethylcuprate, trapping of the intermediate enolate with benzeneselenenyl bromide and oxidation with H2O2. Analogously, (E/Z)‐7‐methyl‐α‐inone ((E/Z)‐12) was obtained in 65% yield from α‐ionone ((E)‐11). 1n, π*‐ Excitation (λ > 347 nm, pentane) of (E)‐7 causes rapid (E/Z)‐isomerization and subsequent reaction of (Z)‐7 to 15 (66%). The formation of 15 is explained by twisting of the dienone chromophore due to repulsive interaction of the 7‐CH3‐group with the CH3‐groups of the cyclohexene ring. On the other hand, irradiation λ > 347 nm, Et2O) of (E)‐7 in the presence of acid leads to (Z)‐7 (5%) and to the novel compound 16 (88%).