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Issue 48, 2018
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Cyclic tris-[5]helicenes with single and triple twisted Möbius topologies and Möbius aromaticity

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Abstract

A number of singly (180°) twisted, largely single-stranded and thus conformationally rather fragile, Möbius molecules have been synthesized within the last 15 years, which are aromatic with 4n electrons, thus violating the Hückel rule. Annulenes with significantly higher twist (e.g. 540°) that retain a full cyclic conjugation path have been elusive, mainly because of the high strain and loss of orbital overlap. Recently, a topological strategy was devised to project the “twist” into “writhe”, thus reducing the strain. However, orbital overlap was still severely reduced within the flexible building blocks. We now present a single and a triple twisted annulene with fully conjugated peripheries. They are unique in their pronounced band shape and conformational robustness as they are made up of three fully kata-condensed [5]helicene fragments. The triple twisted molecule exhibits a strong diatropic ring current in the outer periphery, even though the π system includes 4n electrons. The diatropic current is counterbalanced by a paratropic current in the σ system, resulting in no net manifestation of macrocyclic aromaticity. The key step of the synthesis of both Möbius compounds is a Perkin condensation of complementary bifunctional bismaleates leading to a flexible macrocycle containing alternating benzene and biphenyl fragments. Subsequent photocyclization yields a separable mixture of rigid diastereomeric tris-helicene macrocycles of the above topologies.

Graphical abstract: Cyclic tris-[5]helicenes with single and triple twisted Möbius topologies and Möbius aromaticity

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Supplementary files

Article information


Submitted
29 Jun 2018
Accepted
14 Nov 2018
First published
16 Nov 2018

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2018,9, 8930-8936
Article type
Edge Article

Cyclic tris-[5]helicenes with single and triple twisted Möbius topologies and Möbius aromaticity

G. Naulet, L. Sturm, A. Robert, P. Dechambenoit, F. Röhricht, R. Herges, H. Bock and F. Durola, Chem. Sci., 2018, 9, 8930
DOI: 10.1039/C8SC02877J

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