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, tetraazacirculenes with four nitrogen atoms had so far been limited to one example with four benzene substituents .
Yoshihiro Miyake and colleagues, Nagoya University, Japan, and colleagues have developed a synthesis approach for tetraazacirculenes (pictured) with different substituents. The team first synthesized the corresponding tetrathiacirculenes, 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 tetraazacirculenes 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 heterocirculenes with tunable optical and electronic properties.
- Synthesis of Tetraazacirculenes from Tetrathiacirculenes through an SNAr-Based Process,
Yuya Nagata, Shohei Kato, Yoshihiro Miyake, Hiroshi Shinokubo,
Org. Lett. 2017.
-  Synthesis of a Tetrabenzotetraazacirculene 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.