Development of aromatic ring coupling reaction that had been unexplored for over 80 years

Associate Professor Hideto Ito and Doctoral Student Yoshifumi Toyama from the Graduate School of Science at Nagoya University and their colleagues have successfully developed a new aromatic ring coupling method called Birch reductive arylation using mechanochemical reactions. Their research was published in Nature Communications.

Polycyclic aromatic hydrocarbons (PAHs) are a group of molecules useful as synthetic precursors for nanographenes and as important basic frameworks for organic electronic materials. Since PAHs are normally very stable and difficult to convert directly, nanographene synthesis required the preparation of functionalized PAHs and stepwise coupling of aromatic rings through cross-coupling reactions. Furthermore, due to the low solubility of PAHs in organic solvents and the limitations of their reaction efficiency, there were restrictions on the functionalized PAHs that could be synthesized.

The research group successfully developed an unexplored aromatic ring coupling reaction (Birch reductive arylation) by performing mechanochemical reactions using metallic lithium, PAHs, and aromatic fluorine compounds, mechanically mixing and agitating solid reactants using a ball mill (grinder).

This reaction requires no organic solvents to dissolve compounds and can be performed in air, at room temperature, and in a short time. It can directly use normally reaction-inactive PAHs such as anthracene, pyrene, fluoranthene, benzotriphenylene, and pentacene that lack functional groups. The group also succeeded in connecting one to four aromatic rings to PAHs in one step and synthesizing large nanographenes from small PAHs in a single reaction jar.

Birch reduction and Birch reductive functionalization are based on aromatic ring conversion reactions known since 1944, but Birch arylation reactions had remained undeveloped for over 80 years and had long been considered "non-proceeding" in textbooks. This breakthrough achievement can be used not only as a new aromatic ring coupling reaction that proceeds rapidly even in air but is also expected to serve as an environmentally friendly solid organic synthesis method that uses minimal organic solvents.

Journal Information
Publication: Nature Communications
Title: Birch reductive arylation by mechanochemical anionic activation of polycyclic aromatic compounds
DOI: 10.1038/s41467-025-60318-y