UVA SELF-PHOTOSENSITIZED OXYGENATION OF B-IONONE¡¨

CLAUDIO D. BORSARELLI, MIRTA MISCHNE, AGUSTINA LA VENIA Y FAUSTINO E. MORÁN VIEYRA

ciudad de Córdoba Argentina

Conferencia; 9a Conferencia Latinoamericana de Físico-Química Orgánica; 2007

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 1,2,4-trioxane (2) and 5,8-endoperoxide (5) derivatives 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, confirmed the formation of the excited triplet state of 1 with a quantum yield FT = 0.50 as the precursor for the generation of singlet oxygen 1O2 (FD = 0.16) and the isomeric a-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 M-1s-1 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 a-pyran ring in the concerted [2+4] cycloaddition of 1O2.