5552-30-7Relevant articles and documents
UVA self-photosensitized oxygenation of β-ionone
Borsarelli, Claudio D.,Mischne, Mirta,Venia, Agustina La,Vieyra, Faustino E. Moran
, p. 1313 - 1318 (2008/09/16)
The steady-state UVA (350 nm) photolysis of (E)-β-ionone (1) in aerated toluene solutions was studied by 1H NMR spectroscopy. The formation of the 1,2,4-trioxane (2) and 5,8-endoperoxide (5) derivatives in the ratio of 4:1 was observed. Time-resolved laser induced experiments at 355 nm, such as laser-flash photolysis, photoacoustic and singlet oxygen 1O2 phosphorescence detection, confirmed the formation of the excited triplet state of 1 with a quantum yield ΦT = 0.50 as the precursor for the generation of singlet oxygen 1O2 (ΦΔ = 0.16) and the isomeric α-pyran derivative (3), which was a reaction intermediate detected by NMR. In turn, the reaction of 1O2 with 1 and 3 occurred with rate constants of 1.0 × 106 and 2.5 × 108 m-1s -1 to yield the oxygenated products 5 and 2, respectively, indicating the relevance of the fixed s-cis configuration in the α-pyran ring in the concerted [2+4] cycloaddition of 1O2.
Photochemical Reactions. 137-th Communication. Preparation and Photolysis of (E/Z)-7-Methyl-β-ionone
Ishii, Keitaro,Mathies, Peter,Nishio, Takehiko,Wolf, Hans Richard,Frei, Bruno,Jeger, Oskar
, p. 1175 - 1183 (2007/10/02)
The title compounds (E/Z)-7 were prepared in 66percent overall yield by reaction of β-ionone ((E)-1) with lithium dimethylcuprate, trapping of the intermediate enolate with benzeneselenyl bromide and oxidation with H2O2.Analogously, (E/Z)-7-methyl-α-ionone ((E/Z)-12) was obtained in 65percent yield from α-ionone ((E)-11). 1n,?*-Excitation (λ > 347 nm, pentane) of (E)-7 causes rapid (E/Z)-isomerization and subsequent reaction of (Z)-7 to 15 (66percent).The formation of 15 is explained by twisting of the dienone chromofore due to repulsive interaction of the 7-CH3-group with the CH3-groups of the cyclohexene ring.On the other hand, irradiation, (λ > 347 nm, Et2O) of (E)-7 in the presence of acid leads to (Z)-7 (5percent) and to the novel compound 16 (88percent).
Photochemistry of Dienones. Part 7. On the Photosensitized Isomerization of (E)-β-Ionone and its Isomeric α-Pyran. Evidence for Exciplex Formation between the α-Pyran anf Fluoren-9-one
Cerfontain, Hans,Geenevasen, Jan A. J.,Noort, Paul C. M. van
, p. 1057 - 1062 (2007/10/02)
The photosensitized (E)-β-ionone (1)-α-pyran (2) isomerization in benzene as a solvent has been studied in some detail.For xanthone, benzophenone, and 1- and 2-acetonaphthone the (1) : (2) photostationary state (p.s.s.) ratio is 3.5 +/- 0.2, whereas for the series of aromatic hydrocarbons studied and the ketones fluoren-9-one and benzanthrone it is 0.37 +/- 0.07, both for a total substrate concentration of ca. 0.1M.The low :> p.s.s. values observed with the second group of sensitizers are not the result of additional singlet sensitization.They are ascribed to a specific additional route of isomerization for the α-pyran via singlet exciplex formation which route is almost negligible for (E)-β-ionone.This explanation is in line with both the Stern-Volmer plots for the quenching of the fluorescence of fluoren-9-one by the α-pyran and by (E)-β-ionone , and by the dependence of /> p.s.s. on the total substrate concentration in the case of fluoren-9-one as a sensitizer.From the dependence of the photostationary state for the triplet photosensitized isomerization on the triplet energy on the sensitizer, it was concluded that the triplet energies of (E)-β-ionone and the isomeric α-pyran (2) are 54-56 and -1, respectively.
