Bicyclic Phenyl-Ethynyl Architectures: Synthesis of a 1,4-Bis(phenylbuta-1,3-diyn-1-yl) Benzene Banister.

Linda Maria Bannwart,Thomas Müntener,Daniel Häussinger,Lukas Jundt,Michel Rickhaus,Marcel Mayor

doi:10.1002/chem.202005207

Linda Maria Bannwart, Thomas Müntener + Show 4 more

Open Access

https://doi.org/10.1002/chem.202005207

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Abstract

The novel diacetylene bridged terphenylic macrocycle 1 is presented and discussed in the context of rotationally restricted “Geländer” oligomers. The 1,4‐bis(phenylbuta‐1,3‐diyn‐1‐yl) benzene bridge of diacetylene 1 is significantly longer than its terphenyl backbone, forcing the bridge to bend around the central pylon. The synthesis of molecule 1 is based to a large extent on acetylene scaffolding strategies, profiting from orthogonal alkyne protection groups to close both macrocyclic subunits by oxidative acetylene coupling sequentially. The spatial arrangement and the dynamic enantiomerization process of the bicyclic target structure 1 are analyzed. In‐depth NMR investigations not only reveal an unexpected spatial arrangement with both oligomer strands bent alongside the backbone, but also display the limited stability of the model compound in the presence of molecular oxygen.

Highlights

The fascination for conjugated macrocycles stems from the combination of structural beauty with well-defined shape and size, and from their intrinsic physical properties.[1,2,3] The synthetic challenges pertaining to shape-persistent macrocycles such as cyclynes and arenecyclynes make them attractive from a methods development viewpoint.[4,5] A beautiful example is the entirely sp-hybridized macrocyclic carbon allotrope reported by Anderson and co-workers recently.[6]
In analogy to our earlier strategy, two oligomers with different lengths were interlinked into a ladder-type structure, forcing the longer oligomer (OPDE as banister) to wrap around the shorter one (oligophenylenes (OP) as axis)
Controlling alkyne protection groups potentially allows for the improved steering of the macrocyclization process

Summary

Introduction

In these new “Geländer” oligomers (Figure 1 c), surprisingly low racemization barriers were observed, they still qualify as atropisomers. The investigations allow to draw two main conclusions concerning the molecular design: i) stability of the compounds decreases with increasing number of diacetylenes or the bridge-length in the oligomer, and ii) the OPDE banister in 1 behaves rather like the banister of a staircase with an inserted floor (Figure 1 f) than a spiral staircase (Figure 1 a)—instead of wrapping helically around the central para-terphenyl axis (Figure 1 d), it bends back on the same side of the axis (Figure 1 e)

Results and Discussion

Conclusions

Conflict of interest