Synthesis of Retro-γ-Ionols and the Corresponding-Ionones1

Abstract Both the direct2 and the sensitized3,4 photolyses of (E)-β-ionol (2) have been studied in some detail. In a preliminary publication5 we have indicated that direct photolyses of (E)-β-ionol (2) with λ = 254 nm yields (Z)-retro-γ-ionol (3) as the primary product; upon further irradiation 3 is converted into the corresponding (E)-isomer (4) which rapidly yields the bicyclic alcohol 5. A quantitative study revealed that the photoconversion of (E)-β-ionol with λ = 254 nm to 3 is about 10 times faster than the conversion of 3 into (E)-retro-γ-ionol.6 This rate difference thus allows the photosynthesis of 3.