Dimethoxycarbene, generated at 110 °C by thermolysis of 2,2-dimethoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazoline, displaces fluoride from aromatic rings that are activated with electron-withdrawing groups. Intermolecular substitution on Sanger's reagent and on hexafluorobenzene are reported, together with intramolecular substitution by a dioxycarbene with a tethered aryl group.Keywords: aromatic substitution, aryl(dimethoxy)fluoromethanes, aryl fluoride, dialkoxycarbene, nucleophilic substitution.