Photoinduced Ring Opening of Methyl 1-Aryl-5-oxo-6,7-dihydro-1<i>H</i>,5<i>H</i>-pyrazolo[1,2-<i>a</i>]pyrazole-2-carboxylates in the Presence of Diaryl Disulfides

Abstract

Among the methods used for the synthesis of functionalized heterocyclic compounds, photochemistry has gained immense popularity due to the reactivity of intermediates in photoinduced reactions. In this study, we report on the effect of diaryl disulfides as hydrogen atom transfer catalysts on the photoinduced transformations of pyrazolo[1,2-a]pyrazolones. After excitation with visible light, these compounds are susceptible to C–N bond cleavage, followed by intermolecular hydrogen atom abstraction. By modifying the reaction conditions, we have developed two novel methods for the synthesis of highly substituted pyrazoles.

Keywords

• pyrazoles
• photochemistry
• hydrogen atom transfer
• disulfides