σ-Bishomoconjugation (σ-Bishomoaromaticity) in 4C/3(2)e Cations—Scope and Limitations

Abstract

For the seco‐dodecahedradiene 1, in which the distance dππ between the carbon atoms of the two double bonds ranges from 2.90 to 3.20 Å and pyramidalization angles Φ range from 14.9 to 35.5°, the geometrical prerequisites for in‐plane (σ)‐homoconjugative (σ‐bishomoaromatic) electron delocalization in 4C/3(2)e cations could be better defined. Whilst the 4C/3e radical cation is persistent in a matrix, the 4C/2e dication in superacid medium is, at best, an intermediate en route to the stable bisallylic dication.

Carbocations in Superacid Systems

“…Dication 585 can be considered as a four-p-electron bicyclo(polycyclo)aromatic system. For 596, only the corresponding bisallylic dication could be observed, 1051,1052 whereas for 597 the dication could not be observed at all. The extent of bishomoaromatic delocalization, as expected, is critically dependent upon structural geometry.…”