[8]Circulenes are macrocycles with an eight-membered “core”. Incorporating heterocycles such as pyrroles into this class of compounds could make them useful for optical and electronic applications. However, tetraaza[8]circulenes with four nitrogen atoms had so far been limited to one example with four benzene substituents [1].

Yoshihiro Miyake and colleagues, Nagoya University, Japan, and colleagues have developed a synthesis approach for tetraaza[8]circulenes (pictured) with different substituents. The team first synthesized the corresponding tetrathia[8]circulenes, which were then oxidized using m-chloroperoxybenzoic acid (mCPBA). The resulting octaoxide was subjected to a nucleophilic aromatic substitution reaction in which amines replace the sulfur groups.

The resulting tetraaza[8]circulenes exhibit bright fluorescence both in solution and in the solid state. The team is also working on using the compounds as p-type semiconductors. According to the researchers, this approach could be useful for the synthesis of other hetero[8]circulenes with tunable optical and electronic properties.

• Synthesis of Tetraaza[8]circulenes from Tetrathia[8]circulenes through an S_NAr-Based Process,
  Yuya Nagata, Shohei Kato, Yoshihiro Miyake, Hiroshi Shinokubo,
  Org. Lett. 2017.
  DOI: 10.1021/acs.orglett.7b01074

Reference

• [1] Synthesis of a Tetrabenzotetraaza[8]circulene by a “Fold-In” Oxidative Fusion Reaction,
  Fengkun Chen, Yong Seok Hong, Soji Shimizu, Dongho Kim, Takayuki Tanaka, Atsuhiro Osuka,
  Angew. Chem. Int.l Ed. 2015, 54, 10639–10642.
  DOI: 10.1002/anie.201505124