Anti‐Aromatic versus Induced Paratropicity: Synthesis and Interrogation of a Dihydro‐diazatrioxa[9]circulene with a Proton Placed Directly above the Central Ring. Issue 13 (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 international edition. Volume 59:Issue 13(2020)
• Page Start: 5144
• Page End: 5150
• Publication Date: 2020-02-20
• Subjects: anti-aromaticity -- circulenes -- fused-ring systems -- nine-membered rings -- NICS values; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201913552
• Languages: English
• ISSNs: 1433-7851

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 : An oxidative coupling within a diazadioxa[10]helicene gives a dihydro‐diazatrioxa[9]circulene, with a proton from a pendant naphthalene moiety centred directly above the central nine‐membered ring. 1 H NMR analysis revealed that this distinct environment induces a significant magnetic deshielding effect on that particular proton.