Abstract: The oxidation of 1,4-diiodo-2,3,5,6-tetramethylbenzene (diiododurene) and 1,4-dibromo-2,3,5,6-tetramethylbenzene (dibromodurene) with lead dioxide (PbO2) in a mixture of hydrogen fluoride and pyridine (Olahʼs reagent) and methylene chloride as co-solvent at room temperature for 96 h afforded the corresponding monofluorination products of one methyl group. This reaction is the first example of using the oxidative system PbO2–HF–Py–CH2Cl2 for the side-chain monofluorination of methylbenzenes.