Organic molecular containers on the nanometer scale have found wide applications in the fields of sensing, purification, and catalysis. The construction of such nanocontainers requires large bowl-shaped molecules, called cavitands, the size of which has been a limiting factor for the construction of large nanocontainers. The cavitand volume is restricted by the size of the structural platform used (diameter approx. 7 Å).

Konrad Tiefenbacher and colleagues, University of Basel, Switzerland, have synthesized a very large bowl-shaped molecule named acridane[4]arene (diameter approx. 14 Å) in six steps and with high yields (38 %). The crucial macrocyclization step involves an acridane precursor and dodecanal in the presence of catalytic amounts of triflic acid.

The macrocycle favors a crown conformation because of the hydrogen bond pattern of the free phenols and the preference of the R substituents for axial orientation. Nanocontainers, deep enough for C₆₀ and C₇₀, were synthesized by functionalizing the macrocycle with quinoxaline walls by nucleophilic aromatic substitution. The so-called megalo-cavitands have volumes of up to 814 ų. The selective binding of fullerene C₇₀ in the presence of C₆₀ was demonstrated.

The researchers anticipate that that the macrocycle will be useful for the construction of a wide range of nanocontainers, including those that are water soluble and able to interact with protein surfaces.

• Megalo‐Cavitands: Synthesis of Acridane[4]arenes and Formation of Large, Deep Cavitands for Selective C70 Uptake,
  Jonathan Pfeuffer-Rooschüz, Salome Heim, Alessandro Prescimone, Konrad Tiefenbacher,
  Angew. Chem. Int. Ed. 2022.
  https://doi.org/10.1002/anie.202209885