Efficient Photooxidation of Aryl(hetaryl)pyrazolines by Benzoquinone

: 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.