Symmetric, Unsymmetrical, and Asymmetric [7]‐, [10]‐, and [13]Helicenes

• Published in: Angewandte Chemie International Edition Vol. 58; no. 51; pp. 18419 - 18423
• Main Authors: Pedersen, Stephan K., Eriksen, Kristina, Pittelkow, Michael
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 16.12.2019; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Asymmetry; Chemistry; Chemistry, Multidisciplinary; chirality; Crystallography; Electronic devices; Enantiomers; Fluorescence; helicenes; NMR; non-planar aromatics; Nuclear magnetic resonance; Physical Sciences; Science & Technology; Spectroscopy; structure–property relationships; Synthesis; synthetic methods; chirality; helicenes; HELICENE; non-planar aromatics; OXAHELICENES; PLANAR; synthetic methods; structure-property relationships
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201910214

Fully aromatic helicenes with more than one pitch‐length are illustrious synthetic targets with potential applications in advanced optical devices and nano‐electronics. The task of extending the length of fully conjugated helicenes past one pitch length is challenging. Now, the synthesis of a series of azaoxa[7]‐, [10]‐, and [13]helicenes is described. The synthesis is based on iterative oxidative furan formation between 3,6‐dihydroxycarbazoles and/or 2‐naphthols. The flexibility of the presented method allows the convenient and scalable synthesis of symmetric, unsymmetrical, and asymmetric homo‐chiral structures. The [13]helicenes can be synthetically functionalized both at the termini and the periphery. The full range of helicenes were characterized using NMR and optical spectroscopy (UV/Vis, fluorescence, and CD) along with single‐crystal X‐ray crystallography. The enantiomers of the [13]helicenes are the longest optically pure helicenes isolated to date. All in a twirl: The gram‐scale synthesis of a series of azaoxa[7]‐, [10]‐, and [13]helicenes is described. The synthesis is based on iterative oxidative furan formation between 3,6‐dihydroxycarbazoles and/or 2‐naphthols. The optically pure [13]helicenes can be synthetically functionalized both at the termini (see picture: blue) and the periphery (red).