A Remarkable [2.2.2]Propellane

Abstract

To explore the effects of fluorine substitution on the highly strained [2.2.2]propellane skeleton, a new representative of this ring system, perfluorotricyclo[2.2.2.01,4]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.

[2.2.2]Propellane Isomerization by Grob Rearrangement: An Ab Initio MR‐AQCC Study

“…In structure 1 all the C-C bond lengths, including the central C1-C4 bond, are very similar and comparable to the C-C bond length in cyclobutane (1.548 Å). [44] The C1-C4 distance of 1.573 Å [19] measured for structure 6 is longer than the calculated value of 1.542 Å in 1. This difference is not unexpected since the [2.2.2]propellane cage in 6 is strongly affected by the fluorine and acetal substituents.…”

“…The synthesis of the thermodynamically stable and heavily fluorinated derivative propellane 6 (unchanged after 10 h at 100°C) supports this conclusion. [19] It is not clear at present whether its existence is a consequence of an increased stability of 1 over 2, a substantial barrier height for bond-stretch isomerism and/ or because of hindered Grob-type fragmentation.…”

“…[17] The heavily fluorinated molecules 5 and 6 have been prepared by Lemal and co-workers. [18,19] Unfortunately, the barriers to the ringopening reactions leading to the corresponding substituted dimethylenecyclohexanes were not measured. We note in passing that Dannenberg and Prociv [20] performed INDO calculations of the lowest singlet and triplet energy hypersurfaces, which indicated that 1 was substantially more stable than 2 and that the former compound could be obtained photochemically via the first triplet state by intersystem crossing.…”

The Influence of Multiple Fluorination on the Ring Opening of [2.2.2]Propellane

“…It is interesting to note that recent attempt to prepare 2a, as well as similar carboxyamido-[2.2.2]propellane derivatives 3a and 4a, by electroreduction of 1,4-dichlorobicyclo[2.2.2]octane-2-carboxamides failed. [14] Further stabilisation of the [ [15,16] The first among them (5a) rearranges to a mixture of the corresponding 1,4-dimethylenecyclohexanes with a half-time of 40 hours at 21 °C, while 6a showed no signs of decomposition even after heating at 100 °C for more than 10 hours.…”

Dehalogenation of 1,3‐Diiodotricyclo[3.3.0.03,7]octane: Generation of 1,3‐Dehydrotricyclo[3.3.0.03,7]octane, a 2,5‐Methano‐Bridged [2.2.1]Propellane

“…[3] The unusual structure of these compounds has attracted, [4] and still attracts, [5] much attention from both experimental and theoretical chemists.For more than 20 years, our group has been working on the synthesis of bisnoradamantane derivatives. We have developed two general entries to this strained carbocyclic skeleton, [6] and have generated, trapped, and dimerized several highly pyramidalized alkenes by dehalogenation of 1,2-diiodobisnoradamantanes.…”