Iron porphyrins-catalysed oxidation of α-alkyl substituted mono and dimethoxylated benzyl alcohols

The mechanisms of oxidation of a series of a-alkyl substituted mono and dimethoxylated benzyl alcohols catalysed by mesotetrakis(4-N-methylpyridynium)porphyrin iron (III) chloride (FeTMPyPCl) and meso-tetrakis(4-sulfonatophenyl)porphyrin iron (III) chloride (FeTSPPCl) in aqueous solution with KHSO5 as oxygen atom donor and by meso-tetrakis(pentafluorophenyl)-porphyrin iron (III) chloride (FeTPFPPCl) in dichloromethane employing iodosylbenzene as oxidant have been investigated. In the highly polar aqueous medium an electron transfer mechanism is operating. With FeTMPyPCl, which is a much more efficient catalyst than FeTSPPCl due to the presence of stronger electron withdrawing substituents, formation of side-chain oxidation products accompanies generation of nuclear oxidation products. In the low polar solvent dichloromethane, two competing mechanism have been suggested: hydrogen atom transfer and formation of a complex between the active species iron-oxo porphyrin radical cation and the substrate.