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Polycyclic conjugated hydrocarbons containing four-membered cyclobutadienoids (CBDs) are of great fundamental and technical interest due to the antiaromaticity brought by CBD circuits. However, their synthesis has been challenging, hampering the exploration and understanding of such systems. We report efficient synthesis of a series of unprecedented [3]naphthylene regioisomers in high yields, where three naphthalenoids are fused through two CBDs in linear, angular, and bent regioconnectivity. Their synthesis was enabled by exclusively regioselective catalytic arene-norbornene annulation (CANAL) between dibromonaphthalenes and benzooxanorbornadienes, followed by aromatization. [3]Naphthylene regioisomers exhibited distinct optoelectronic properties. Nucleus-independent chemical shift calculations, NMR spectroscopy, and X-ray crystallography revealed the strong effect of the fusion pattern on the local antiaromaticity and aromaticity in fused CBDs and naphthalenoids, respectively. Thus, our synthetic strategy allows facile access to extended CBD-fused ??-systems with tunable local antiaromaticity and aromaticity.


Konishi, A.; Okada, Y.; Nakano, M.; Sugisaki, K.; Sato, K.; Takui, T.; Yasuda, M., "Synthesis and Characterization of Dibenzo[a,f]pentalene: Harmonization of the Antiaromatic and Singlet Biradical Character." J. Am. Chem. Soc. 2017, 139, 15284Jin, Z.; Teo,...
Antiaromatic compounds by definition are unstable and so difficult to prepare. One approach to increase their stability is to fuse aromatic ring(s) onto the antiaromatic system. I discuss in this blog post two different scaffolds where this approach has been...