Preparation of 4-fluorophenol and 4-fluorobenzoic acid by the Baeyer-Villiger reaction

The possibility of preparing 4-fluorophenol or 4-fluorobenzoic acid via the Baeyer-Villiger reaction starting from unsymmetrical fluoroaryl ketones is discussed. Several unsymmetrical 4-fluorobenzophenones having different substituents in the fluorine-free aryl group were prepared and converted to esters by treatment with peracetic acid. The electrophilicity of the substituents influenced the molecular structure of the ester formed as a result of a carbon-to-oxygen migration, and hence 4-fluorophenol or 4-fluorobenzoic acid formation. Electron-withdrawing substituents favoured the formation of 4-fluorophenol in good yield, while electron-donating substituents formed 4-fluorobenzoic acid preferentially.