The water-soluble iron (III)[TF5PS4P= meso-tetrakis (pentafluorophenyl)-β- tetrasulfonatoporphyrin] catalyses the selective oxidation, by magnesium monoperoxyphthalate (or H2O2), of 1, 2-dimethoxyarenes bearing an electron-withdrawing substituent (CN, CHO, COR) to muconic dimethyl esters which are formed in 30–40% yield and are the only reaction products obtained after CH2Cl2 extraction.