Photochemical reactions. 137 th communication . Preparation and photolysis of ( E / Z )‐7‐methyl‐β‐ionone

The 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 H 2 O 2 . Analogously, ( E/Z )‐7‐methyl‐α‐inone (( E/Z )‐ 12 ) was obtained in 65% yield from α‐ionone (( E )‐ 11 ). 1 n, 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‐CH 3 ‐group with the CH 3 ‐groups of the cyclohexene ring. On the other hand, irradiation λ > 347 nm, Et 2 O) of ( E )‐ 7 in the presence of acid leads to ( Z )‐ 7 (5%) and to the novel compound 16 (88%).