Photochemical Reactions. 149 th Communication. Photochemistry of 7,8‐dihydro‐4‐hydroxy‐β‐ionone and derivatives

The photolysis of 7,8‐dihydro‐4‐hydroxy‐β‐ionone ( 6 ) was investigated together with its acetate and isopropyl ether 7 and 8 , respectively. Irradiation (λ > 245 nm) of 6 in MeCN or i‐PrOH at temperatures between 25° and −65° leads to the tricyclic ethers 9 , 10 and 13A + B , and to the spirocyclic ethers 11 and 12 , which are all known types of photoproducts, previously obtained on photolysis of 7,8‐dihydro‐β‐ionone ( 1 ). The same types of products are obtained on irradiation of the acetate 7 and the isopropyl ether 8 . On the other hand, irradiation of the hydroxy compound 6 in MeCN or i‐PrOH at temperatures between −35° and −65° leads to the new tricyclic tertiary alcohols 14 and 15 as the major products. Their formation involves an intramolecular trapping of a carbocation by the neighbouring OH group, thus, supporting the previously proposed mechanism of the transformation 1 → 5. For structure proof, the tricyclic alcohol 14 and the pheny1 carbamate 42 , derived from 9 , were subjected to X‐ray analysis.