Photochemical intramolecular acylation of 3-(2-hydroxybenzylidene)-4,5-dihydrofuran-2(3H)-one in methanol

Abstract

The dependence of the kinetics on the wavelenghth of trans-3-(2-hydroxybenzylidene)-4,5-dihydrofuran-2(3H)-one was studied at 220–360 nm in methanol solution for the two consecutive photochemical reactions, geometrical isomerization of the trans- and intramolecular acylation of the cis-substrate. Quantum yields for the first reaction were higher (at 5.20 × 10^–5M) than those for the second. The effect of concentration quenching on quantum yields for the latter process was found to be appreciable in the 10^–4–10^–5M range. This reaction appears to proceed through long-lived T₂ states, while isomerization occurs either directly from the singlet excited state S₁ or indirectly by crossing of S₁ to a triplet excited state T₁.