Two easy photochemical methods for the conversion of commercial ionone alpha into regioisomerically enriched gamma-ionone and gamma-dihydroionone

Commercial ionone alpha was converted into regioisomerically enriched gamma-ionone and gamma-dihydroionone by mean of two synthetic routes, each involving a photochemical reaction as a key step. Using visible light, oxygen and methylene blue as photosensitizer, ionone alpha was transformed in 4-hydroxy-gamma-ionone isomers, which were deoxygenated to afford gamma-ionone by mean of triethylammonium formate in the presence of (Ph3P)(2)PdCl2 as catalyst. Irradiation of dihydro-a-ionol acetate, using high-pressure mercury lamps and xylene as photosensitizer afforded gamma-dihydroionol acetate, which, after purification by crystallization of the corresponding p-nitrobenzoyl ester, was converted to pure gamma-dihydroionone.