Selective nucleophilic aromatic substitution of 2-(polyfluorophenyl)-4H-chromen-4-ones with pyrazole

Abstract

The formation of various fluorine atoms substitution products in Cs2CO3-promoted SNAr reactions of 2-(polyfluoroaryl)-4H-chromen-4-ones with pyrazole in refluxing MeCN was shown. Selective synthesis of mono(1H-pyrazol-1-yl)- and per(1H-pyrazol-1-yl)flavones was performed in the presence of NaOBut at room temperature using different pyrazole and base equivalents. A mechanism for fluorine atoms substitution in 2-(pentafluorophenyl)-4H-chromen-4-one by sodium pyrazolide was proposed. The structures of pyrazolyl-substituted flavones were established based on the combined analysis of NMR and XRD data.