Octafluorobicyclo[2.2.0]hex-1(4)-ene: A Greatly Strained Alkene with Novel Reactivity

摘要

The hydrocarbon bicyclo[2.2.0]hex-1(4)-ene (1), which was prepared and studied by the Wiberg group, is highly reactive as a consequence of its severe angle strain. With the expectation that its fully fluorinated analog 2 would manifest very different but comparably interesting chemistry, we have synthesized this perfluoroalkene and trapped it with a variety of reagents. A precursor for 2, dibromide 5, was prepared in three steps from hexafluorobenzene as shown in Scheme 1. Vapor-phase photoisomerization of the benzene to its Dewar isomer 3 was followed by treatment with aluminum bromide to effect selective replacement of the bridgehead fluorines with bromines, giving 4. Because it aromatizes even in the cold and especially because it tends to detonate capriciously, 4 was generally carried on without purification. Low temperature fluorination with 30% fluorine/helium transformed 4 into saturated dibromide 5.