Boroxines are six-membered (B–O)3 rings reversibly formed by dehydration of boronic acids and exhibit Lewis acidity. Using this reversible bond formations, we successfully constructed a series of boroxine cages[1] and clarified the unique dynamic interconversion between cages.[2]

We also developed an efficient method for the synthesis of macrocycles using boroxines as covalent templates.[3] This method enables the synthesis of macrocycles bearing three boronate units from the corresponding boronic acids. The introduction of tethers into the boronic acid substrates allows the synthesis of larger macrocycles, which can subsequently be converted into macrocycles functionalized with three corresponding functional groups by cleavage of the tethers. Furthermore, this method can be applied to site-selective
cross-linking reactions, enabling the efficient synthesis of linear diboronic esters.

The resulting macrocyclic triboronic acid undergoes selective intramolecular boroxine formation to quantitatively afford a tricyclic boroxine.[4] This transformation is accompanied by changes in the physical properties of the molecule and proceeds reversibly upon thermal cycling. 

Notably, the resulting tricyclic boroxine is entropically stabilized and exhibits enhanced hydrostability.[5] In this presentation, I will also discuss our recent work on the synthesis of endo-functionalized oligophenylene rings and cages focusing on the dynamic behavior and applications as porous materials. [6-8]

[1] K. Ono, K. Johmoto, N. Yasuda, H. Uekusa, S. Fujii, M. Kiguchi, N. Iwasawa, J. Am. Chem. Soc. 2015, 137, 7015–7018.
[2] K. Ono, S. Shimo, K. Takahashi, N. Yasuda, H. Uekusa, N. Iwasawa, Angew. Chem. Int. Ed. 2018, 57, 3113–33317.
[3] K. Ono, S. Onodera, H. Kawai, Chem. Commun. 2022, 58, 12544–12547.
[4] K. Ono, K. Sawanaga, S. Onodera, H. Kawai, K. Goto, Chem. Eur. J. 2023, 29, e202300995.
[5] K. Ono, Asian. J. Org. Chem. 2025, 14, e202400683.
[6] K. Ono, Y. Tanaka, K. Sugimoto, S. Kinubari, H. Kawai, ACS Omega 2022, 7, 45347–45352.
[7] K. Ono, T. Ishikawa, S. Masano, H. Kawai, K. Goto, J. Am. Chem. Soc. 2024, 146, 21417–21427.
[8] K. Ono, F. Sasamori, H. Izawa, H. Baba, S. Masano, R. Shirataki, H. Kawai, K. Goto, J. Am. Chem. Soc. 2025, 147, 24473–24481.