1.3- Dehydro-5,7-adamantanediyl

The l,3-dehydro-5,7-adamantanediyl dication, 160, was obtained through the ionization of l,3-dehydro-5,7-difluoroadamantane (159). This dication shows three-dimensional... 

There are several other carbodications that may be represented as 1,3-dicationic systems (or nonclassical, highly delocalized systems), including Schleyer s l,3-dehydro-5,7-adamantanediyl dication (28),11 Hogeveen s pyramidal dication (29),12 diallyl dications (i.e., 30),13 dicationic ethers (i.e., 31),14 diprotonated pyrones (32),15 as well as various aromatic dications. 

Schleyer, P. v. R., Bremer, M., Schotz, K., Kausch, M. Schindler, M. 1987 Four-center two-electron bonding in a tetrahedral topology. Experimental realization of three-dimensional homoaromaticity in the l,3-dehydro-5,7-adamantanediyl dication. Angew. Chem. Int. Ed. Engl. 26, 761 763. 

Extension of the concepts of ribbon and surface delocalization of electrons to three-dimensions leads to volume delocalization and covers cases of radial aromaticity and three-dimensional (3D) aromaticity . As we will show later the most convicing example of radial aromaticity, namely the l,3-dehydro-5,7-adamantanediyl cation (Figure 2), is actually an example of homoradial aromaticity. Also, there exist several examples of homo-3D aromaticity that are normally listed under 3D-aromaticity (for an example, see Figure 2). Finally, a number of examples have been investigated that can be classified as homoheteroaromatic systems (Figure 2). It may be only a matter of time until the first molecule with homospherical aromaticity has been synthesized and investigated. 

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