engleski

Photochemical Rearrangement of 2, 6-di(p-tolyl)-4H- pyran-4-one

Pyrones, biologically active compounds, are fundamental moieties of many naturally occurring compounds, as well as many synthetic compounds. They have numerous applications in medicine as pharmaceuticals, in agriculture as pesticides, and are often used as photosensitizers. Derivative of γ-pyrone 2, 6-di(p-tolyl)-4H-pyran-4-one was previously prepared by microwave-assisted decarboxylation of 6-p-tolyl-3-p-toluyl-dihydro- pyran-2, 4-dione. Exposure of solution of compound 1 in dichloromethane to UV radiation (λ = 256 nm) led to changes in its absorption spectrum. The appearance of isosbestic points suggests equilibrium between at least two species in solution: compound 1 and one or more photoproducts. From the reaction mixture a product of photochemical rearrangement 4, 6-di(p-tolyl)- pyran-2-one (2) was isolated, which was confirmed by IR, 1H-NMR, 13C-NMR spectra. Absorption and emission spectra of compound 2 have been studied and compared to corresponding spectra of compound 1. These spectra give information about the molecular electronic transitions, essential for determination of reaction mechanisms and prediction of the curse of photoreaction. Further on, DFT calculations were made to get more insight on the mechanism of this photochemical rearrangement. Structural characteristics of the isolated photoproduct 2 were also compared to that those of unsubstituted α-pyrone.

MO calculations; molecular structure; photochemical rearrangement; γ-pyrone; UV/Vis spectroscopy

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