A Remarkable [2.2.2]Propellane

To explore the effects of fluorine substitution on the highly strained [2.2.2]propellane skeleton, a new representative of this ring system, perfluorotricyclo[2.2.2.0^1,4]octan-2-one ethylene ketal, was prepared by a rapid and quantitative [2+2] cycloaddition to the strained alkene perfluorobicyclo[2.2.0]hex-1(4)-ene. The propellane displays impressive thermal stability, and the vulnerable C−C bond joining the bridgeheads is very resistant to attack by electrophilic reagents. On the other hand, that electron-deficient bond is cleaved quickly at room temperature by a variety of nucleophiles and mild reducing agents. The behavior of this compound contrasts dramatically with that of the only known [2.2.2]propellane lacking fluorine substituents.