Stable ten-component sandwich compounds have been characterized in which four lithium ions reside between two tetraanions derived from corannulene or its alkyl-substituted derivatives and four additional lithium ions decorate the exterior. In tetrahydrofuran solution, the four lithium ions inside the sandwich can exchange environments with the four external lithium atoms, but the two tetraanion decks of the sandwich never separate from one another on the time scale of nuclear magnetic resonance. Theoretical calculations point to a "stacked bowl" conformation and a low energy barrier for synchronous double inversion of the tetraanion bowls in the solvated sandwich compounds.

This tutorial review discusses synthetic strategies towards aromatic belts, defined here as double-stranded conjugated macrocycles, such as [n]cyclacenes, [n]cyclophenacenes, Schlüter belt, and Vögtle belt. Their appeal stems, firstly, from the unique nature of their conjugation, having p orbitals oriented radially rather than perpendicular to the plane of the macrocycle. Secondly, as aromatic belts are model compounds of carbon nanotubes of different chiralities, a synthetic strategy towards the buildup of structural strain in these compounds could finally open a route towards rational chemical synthesis of carbon nanotubes. The elusiveness of these compounds has stimulated fascinating and ingenious synthetic strategies over the last decades. The various strategies are classified here by their approach to the buildup of structural strain, which is the main obstacle in the preparation of these curved polyarenes.

The reduction of 3He@C60 and 3He@C70 by lithium metal to give solutions of the corresponding hexaanions in THF-d 8 has been achieved under gentle conditions, at subambient temperatures, without sonication, by capitalizing on the ability of corannulene (1) to serve as an efficient electron carrier between the lithium metal and the solid fullerenes, which are virtually insoluble in the reaction medium. The 3He inside the C60 hexaanion is found to be more strongly shielded (by nearly 20 ppm!) than any previously reported 3He in a fullerene [δ(3He@C60 6-) = −48.7 ppm, relative to dissolved 3He gas in the solution], whereas the 3He inside the C70 hexaanion is actually deshielded [δ(3He@C70 6-) = +8.3 ppm], resonating at nearly 15 ppm lower field than any previously reported 3He in a fullerene. These results stand in complete accord with earlier predictions that the magnetic properties of C60 and C70 would be altered dramatically, and in opposite directions, by reduction of the fullerenes to their hexaanions. The phenomenal ability of C60 6- to shield an endohedral 3He from a powerful external magnetic field provides the most compelling evidence to date for the ability of electrons to move freely about the surface of a spheroidal π-system.