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

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.

Geländer Molecules with Orthogonal Joints: Synthesis of Macrocyclic Dimers

“…The formed banister structure in macrocycle 2 obtained upon ring closing consists exclusively of sp 2 and sp hybridized carbon atoms, and thus, its π‐electrons are delocalized over the entire banister. However, in the past, the strained 1,3‐butadiyne motif in the banister turned out to be the origin of pronounced reactivity handicapping the “Geländer” molecule's stability [8,9] . To avoid such stability limitations, we profit from the reactivity of the 1,3‐butadiyne subunit in 2 as the precursor of a thiophene connecting banister building block in 1 .…”

“…Even so complete consumption of deprotected 7 was indicated by matrix‐assisted laser desorption‐ionization mass spectrometry (MALDI‐MS), neither the desired macrocycle nor a conclusive side product could be isolated by CC from the reaction mixture. As alternative Eglinton‐Breslow conditions were explored, which were previously successfully used in our laboratories to form strained butadiynes [8,9] . Again the desired macrocycle was observed by both MALDI‐MS and high‐performance liquid chromatography coupled electron‐spray ionization mass spectrometry (HPLC‐ESI‐MS).…”

“…Our retrosynthetic considerations are sketched in Scheme 1. Due to our successful experience in the past, [8][9][10][11][12][13] an oxidative acetylene coupling was chosen as macro-Scheme 1. Retrosynthetic analysis: Assembly strategy for the macrocycles 1 and 2 from accessible precursors.…”

“…In the last years, we synthesized various “Geländer” structures with oligophenylene (OP) backbones, wrapped by benzylic ethers, [3–5] sulfones, [6] or oligophenylene ethanes (Figure 1D) [7] . Recently, we even enlarged the radius of the design by interlinking both oligomers by alkynes and wrapped para ‐oligophenylene diyne around the OP backbone as a conjugated banister (Figure 1E) [8,9] . However, the strained diynes in the banister subunits displayed enlarged reactivity towards oxygen, reducing the stability of these model compounds considerably.…”

Solid-State and Theoretical Investigations of Some Banister-Type Macrocycles with 2,2’-Aldoxime-1,1’-Biphenyl Units

“…A step forward in the field was brought by the axial helical structures named geländer (the German word for banister) molecules (II-IV, Chart 1), a concept introduced by Vögtle referring to bridged 2,2'-biphenyls, leading to increase hindrance in the racemization process (Mislow et al, 1964;Kiupel et al, 1998;Eshdat et al, 1999;Wolf and Bentley, 2013;Zhang et al, 2016). These compounds reveal spectacular helical structures and high optical activity in a range close to that found for [n]helicenes (Modjewski et al, 2009;Takaishi et al, 2010;Rotzler et al, 2013;Rickhaus et al, 2014;Bannwart et al, 2017;Mannancherry et al, 2018;Bannwart et al, 2021).…”