Anti‐Aromatic versus Induced Paratropicity: Synthesis and Interrogation of a Dihydro‐diazatrioxa[9]circulene with a Proton Placed Directly above the Central Ring. (20th February 2020)

• Record Type: Journal Article
• Authors: Pedersen, Stephan K.; Eriksen, Kristina; Karaush‐Karmazin, Nataliya N.; Minaev, Boris; Ågren, Hans; Baryshnikov, Gleb V.; Pittelkow, Michael
• Is Part Of: Angewandte Chemie. Volume 132:Number 13(2020)
• Page Start: 5182
• Page End: 5188
• Publication Date: 2020-02-20
• Subjects: Antiaromatizität -- Circulene -- Kondensierte Ringe -- Neungliedrige Ringe -- NICS-Werte; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.201913552
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: We present a high‐yielding intramolecular oxidative coupling within a diazadioxa[10]helicene to give a dihydro‐diazatrioxa[9]circulene. This is the first [ n ]circulene containing more than eight ortho ‐annulated rings ( n >8). The single‐crystal X‐ray structure reveals a tight columnar packing, with a proton from a pendant naphthalene moiety centred directly above the central nine‐membered ring. This distinct environment induces a significant magnetic deshielding effect on that particular proton as determined by 1 H NMR spectroscopy. The origin of the deshielding effect was investigated computationally in terms of the NICS values. It is established that the deshielding effect originates from an induced paratropic ring current from the seven aromatic rings of the [9]circulene structure, and is not due to the nine‐membered ring being antiaromatic. UV/Vis spectroscopy reveals more efficient conjugation in the prepared diazatrioxa[9]circulene compared to the parent helical azaoxa[10]helicenes, and DFT calculations, including energy levels, confirm the experimental observations. Abstract : Eine oxidative Kupplung in einem Diazadioxa[10]helicen ergibt ein Dihydrodiazatrioxa[9]circulen, in dem das Proton eines Naphthalinrests direkt über dem zentralen neungliedrigen Ring liegt. 1 H‐NMR‐Analysen zeigen, dass diese besondere Umgebung zu einer deutlichen magnetischen Entschirmung des Protons führt.