Two perhalo-1,4-dioxins, representatives of a previously unknown class of compounds, have been synthesized and shown to exhibit unusual reactivity. In particular, reaction with oxygen is spontaneous and exothermic, and radical-catalyzed homopolymerization will proceed through a fluorinated double bond. Representatives of the perhalo-2,3-dihydro-1,4-dioxin class have also been prepared and found to have reactivity in general intermediate to that of the perhalodioxoles and acyclic trifluorovinyl ethers. Computational studies of the two systems established that introduction of the first double bond raises the energy substantially, while the second double bond results in a near-planar ring with dramatically increased energy content.