Efficient Photooxidation of Aryl(hetaryl)pyrazolines by Benzoquinone

Abstract

Photooxidation of aryl(hetaryl)pyrazolines in the presence of benzoquinone has been studied in organic solvents. This reaction occurs at high rate to provide the corresponding pyrazole in a good yield. The effects of the solvent, pyrazoline structure and oxygen provide definite information on the reaction pathway. It appears that radical species are intermediates in the photooxidation of aryl(hetaryl)pyrazolines in the presence of benzoquinone. A comparison of the new results with the photooxidation of aryl(hetaryl)pyrazolines in the presence of perchloroalkanes is also discussed.

Effect of linker length on the spectroscopic properties of bacteriochlorin – 1,8-naphthalimide conjugates for fluorescence-guided photodynamic therapy

“…Aiming to rationalize these results, we supposed that five-membered heterocyclic ring at C-4 position of the naphthalimide fragment could be oxidized to form 4-pyrazolyl group (Scheme 2). Such oxidation has been previously found for 1,3-diaryland 1,3,5-triaryl-2-pyrazolines [21][22][23][24] as well as for pyrazolinesubstituted coumarins [25][26][27] either upon irradiation in the presence of oxygen or even when irradiation in degassed solution is applied. The possible mechanism involves sensitization of singlet oxygen formation by a dye molecule or, alternatively, the electron transfer from the photoexcited chromophore to the solvent (especially for solvents like CCl 4 or C 2 Cl 6 ).…”