PAHs Containing both Heptagon and Pentagon: Corannulene Extension by [5+2] Annulation

• Published in: European journal of organic chemistry 2022-02, Vol.2022 (5), p.n/a
• Main Authors: Schnitzlein, Matthias, Mützel, Carina, Shoyama, Kazutaka, Farrell, Jeffrey M., Würthner, Frank
• Format: Article
• Language: English
• Subjects: Annulation; Aromaticity; Azulene; Chemical reactions; Corannulene; Enantiomers; Energy gap; Organic chemistry; Polycyclic aromatic hydrocarbons; Visible spectrum
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.202101273

Utilizing Pd‐catalyzed [5+2] annulation a series of heptagon‐extended corannulenes could be synthesized from a borinic acid precursor furnished by C−H borylation strategy. Single‐crystal X‐ray analysis revealed the presence of two conformational enantiomers crystallizing in a racemic mixture. Through their embedded five‐ and seven‐membered rings these polycyclic aromatic hydrocarbons (PAHs) exhibit both negative and positive curvature and UV/Vis/NIR absorption spectroscopy as well as cyclic voltammetry experiments provided insights into the influence of larger flanking aromatic systems and electron‐donating substituents encompassing the heptagonal ring. Through [5+2] annulation of acenaphthylene an azulene‐containing PAH with intriguing optoelectronical properties including a very small bandgap and absorption over the whole visible spectrum could be obtained. Theoretical calculations were employed to elucidate the long‐wavelength absorption and aromaticity. A general synthetic method based on hydroboration, electrophilic borylation, dehydrogenation and [5+2] annulation affords molecules with both bowl‐ and saddle‐shape and the inclusion of a formal azulene unit. Their optical and electronic properties were studied to elucidate the ramifications of different substituents. Furthermore, their aromaticity was assessed through theoretical calculations.