Cationic derivatives of bicyclo[4.2.1]nona-2,4,7-triene as model systems for ground-state Möbius aromaticity

A number of syn-C10 carbocations of bicyclo[4.2.1]nona-2,4,7-triene 1 are described, furnishing possible model systems for the investigation of ground-state Möbius aromaticity. Sign inversion, necessary for 4-p-electron aromaticity, is realized by a simple orientation of the C10 p orbital which is homoconjugated with C2,5. 13C and 1H NMR spectroscopy suggest that the empty orbital at C10 is orientated perpendicularly with respect to the mirror plane of the cations. The saturated analogues of these cations also adopt this configuration. The chemical shift differences between the unsaturated cations and the saturated derivatives suggest a charge delocalization via Möbius aromaticity.