UVA self-photosensitized oxygenation of b-ionone

C. D. BORSARELLI; M. MICHNE; A. LA VENIA; F.E. MORÁN VIEYRA

Los Cocos, Córdoba, Argentina

Conferencia; 9TH LATIN AMERICAN CONFERENCE ON PHYSICAL ORGANIC CHEMISTRY; 2007

UNC

The steady-state UVA (350 nm) photolysis of (E)-b-ionone (1) in aerated toluene solutions was studied by 1H NMR spectroscopy. The formation of the isomeric a-pyran derivative (2) as a reaction intermediate and the end-products 1,2,4-trioxane (3) and 5,8-endoperoxide (4) in a ratio 4:1 was observed. Time-resolved laser induced experiments at 355 nm, such as laser-flash photolysis, photoacoustic, and singlet oxygen 1O2 phosphorescence detection, confirm the formation of the excited triplet state of 1 with a quantum yield FT = 0.50, which in turns was the precursor for the generation of singlet oxygen 1O2 (FD = 0.16). In turn, the reaction of 1O2 with 1 and 2 occurred with rate constants of 1.0´106 M-1s-1 and 2.5´108 M-1s-1 to yield the oxygenated products 4 and 3, respectively, indicating the relevance of the fixed s-cis configuration in the a-pyran ring in the concerted [2+4] cycloaddition of 1O2.    Acknowledgements: The authors thank the financial support from the Argentinian Funding Agencies CONICET, ANCPyT (PICTO 764), CICyT-UNSE, and Fundación Josefina Pratts