A Triply [5]Helicene‐Bridged (1,3,5)Cyclophane

Abstract

A rigid propeller‐shaped conjugated triple macrocycle consisting of two nearly perfectly stacked benzene rings and three linking [5]helicene moieties has been synthesized using a glyoxylic Perkin approach. Analysis of the electron delocalization in this atypical aromatic molecule revealed global aromaticity and a 78 π‐electron circuit along the edge of its triple loop, to the detriment of the two 6 π‐electron circuits in the two stacked benzene rings.

Understanding Aromaticity in [5]Helicene-Bridged Cyclophanes: A Comprehensive Study

“…Both molecules can be viewed as [2,2]paracyclophanes, but instead of being connected by C–C bridges, they are linked by helicenes (see Figure ). These kinds of molecules with chiral topologies are particularly appealing due to their exceptional optical properties, which can potentially be used in electronic applications. − The aromatic nature is another interesting property of these molecules, , as the electron delocalization along the nonplanar structures can significantly contribute to their stability …”

“…Unlike other globally aromatic systems, 10 there is a discontinuity in their EDDB isosurfaces. 2 However, the existence of C−C single bonds does not necessarily imply an interruption of the current−density flux. 30 For instance, charged species of cycloparaphenylenes have been reported, in which C− C single bonds connect their 6-MRs, yet this does not prevent the existence of a global ring current, 31,32 and global aromaticity.…”

“…1−7 The aromatic nature is another interesting property of these molecules, 8,9 as the electron delocalization along the nonplanar structures can significantly contribute to their stability. 10 In the study by Aribot et al, 2 the aromaticity of the triply [5]helicene-bridged (1,3,5)cyclophane was investigated by performing calculations of the magnetic response and using the electron density of delocalized bonds 11 (EDDB) function approach. The authors claimed that II exhibits a diatropic global 78 π-electron current−density response to an external magnetic field.…”

“…The helicene arms and the central stacked 6-MR are linked by three bridges consisting of C−C single bonds. Both molecules can be viewed as [2,2]paracyclophanes, but instead of being connected by C− C bridges, they are linked by helicenes (see Figure 1). These kinds of molecules with chiral topologies are particularly appealing due to their exceptional optical properties, which can potentially be used in electronic applications.…”

“…Recently, Kubo et al reported the synthesis of an eight-shaped molecule ( I , Figure ) composed of two [5]­helicenes connected to two stacked six-membered rings (6-MRs), resulting in a doubly [5]­helicene-bridged (1,4)­cyclophane . In a more recent paper by Aribot et al, they reported a structurally similar propeller-shaped molecule ( II ), consisting of three [5]­helicenes joined at their ends by two stacked 6-MRs. The helicene arms and the central stacked 6-MR are linked by three bridges consisting of C–C single bonds.…”