Four‐Center Two‐Electron Bonding in a Tetrahedral Topology. Experimental Realization of Three‐Dimensional Homoaromaticity in the 1,3‐Dehydro‐5,7‐adamantanediyl Dication

A nonclassical structure for the dication 3 is supported, in particular, by the 13C-NMR data: the signals of the bridgehead C atoms are shifted upfield (δ = 6.6) and not downfield, as would have been expected for a classical dication. The resonances of the methylene C atoms are observed at δ = 35.6 (1H-NMR: δ = 3.8). Compound 3 is synthesized starting from 1,3,5,7-tetra-iodoadamantane, which reacts with HgF2 to give 1. Compound 1 reacts with nBuLi to give 2, from which 3 can be generated. The dication 3 is stable up to 0°C.