Temperature‐Driven Planar Chirality Switching of a Pillar[5]arene‐Based Molecular Universal Joint

Abstract

The study of an enantiopure bicyclic pillar[5]arene-based molecular universal joint (MUJ) by single-crystal X-ray diffraction allowed for the first time the unequivocal assignment of the absolute configuration of a planar chiral pillar[5]arene by circular dichroism spectroscopy. Crucially, the absolute configuration of the MUJ was switched reversibly by temperature, with an accompanying sign inversion of the anisotropy factor that varied by as much as 0.03, which is the largest value ever reported. Mechanistically, the reversible chirality switching of the MUJ is driven by the threading/dethreading motion of the fused ring and hence is dependent on both the size and nature of the ring and the solvent employed, reflecting the critical balance between the self-complexation of the ring by pillar[5]arene, the solvation to the excluded ring, and the inclusion of solvent molecules in the cavity.

Diastereoselective Photocycloaddition Reaction of Vinyl Ether Tethered to 1,4‐Naphthoquinone

“…Along with the determination of the absolute configuration, chiroptical methods, combined with theoretical investigation, becomes a versatile tool to investigate the conformational behavior of chiral molecule in condensed phase ,. Among these, the circular dichroism (CD) spectra are one of the profound and most used method for this purpose ,,,,. Figure shows the experimental CD spectra of ( R )‐ 1 in methylcyclohexane at 25 °C, together with theoretically predicted CD spectra for pro‐( R 3 ) and pro‐( S 3 ) conformers of ( R )‐ 1 .…”

“…[35,36] Among these, the circular dichroism (CD) spectra are one of the profound and most used method for this purpose. [37,38,39,40,41] Figure 5 shows the experimental CD spectra of (R)-1 in methylcyclohexane at 25°C, together with theoretically predicted CD spectra for pro-(R 3 ) and pro-(S 3 ) conformers of (R)-1. As the theoretical spectra were nearly mirror-imaged to each other, the observed experimental spectrum can be understood as the pro-(R 3 ) and pro-(S 3 ) conformers are in equilibrium and the latter is slightly preferred under the condition.…”

A Diaminopillar[5]arene‐Based Macrobicyclic Molecule: Synthesis, Characterization and A Lock–Key Story

“…1,4‐dicyanobutane ( DB ) has been proved to form highly stable host–guest complexes with pillar[5]arenes and the binding constant ( K a >10 4 m −1 ) was much larger than those of pillar[5]arene and linear alkanes ( K a =10–100 m −1 ) . Thus, introducing DB into a pillar[5]arene‐based macrobicyclic molecule system would switch the bicyclic molecule from the “in” to “out” state in some extent, which in the 1 H NMR spectrum would appear as chemical shifts changes, if there were “in” state molecules . Thus, we used DB to study the state of BC‐DAP5 in solution.…”

“…However, such studies are rare. It will be very interesting if we could control the motion of one or more phenylu nites of pillar[5]arenes, making the rotation have an on/off state.Recently,s everalp illar[5]arene-based macrobicyclic molecules have been reported, [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] and some of them showeda n [a] Dr.Supporting information and the ORCID identification number(s) for the author(s) of this articlecan be found under: https://doi.Scheme2.The schematicrepresentation of the reversible control of BC-DAP5 locked and unlocked states.…”

Chiral Bambusurils for Enantioselective Recognition of Carboxylate Anion Guests

“…[4] Chiral macrocyclic compounds are particularly interesting for this purpose,a st hey can attract enantiomeric guests with reasonable affinity,b ut also with enantiomeric selectivity,d ue to steric repulsions, which differ for both enantiomers. Among others, cyclodextrins, [5] calixarenes, [6] pillararenes, [7] cucurbiturils, [8][9][10] and crown ethers [11] play ad ominant role in enantiomer sensing.C yclodextrins are composed from chiral a-d-glucopyranosideu nits;t herefore, by their nature they are homochiral. On the other hand, the chirality of calixarenes and crown ethers is induced via the attachment of chiral substituents or when the symmetry of the macrocycle is broken,g iving rise to inherently chiral compounds.…”