AbstractThe photochemistry of1band2b,i.e.the valeryl analogues of (E)‐α‐ (1a) and (E)‐β‐ionone (2a), respectively, has been studied.Upon irradiation with λ 254 and 300 nm, the α‐isomer1bexhibits the same reactions as the parent ionone1a,viz.(E)‐(Z) isomerization, followed by photo‐deconjugation and subsequent α‐cleavage with formation of the 1,3‐ and 1,5‐acyl shift isomers. Upon irradiation of the β‐isomer2bwith λ 254 nm, only the α‐pyran isomer15is formed, although extensive polymerization does occur. Neither the α‐ nor the β‐isomer yields any detectable product resulting from a Norrish type II reaction in which the γ