Perspectives on push–pull chromophores derived from click-type [2 + 2] cycloaddition–retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes

• Michio Yamada

Beilstein J. Org. Chem. 2024, 20, 125–154, doi:10.3762/bjoc.20.13

• -phenanthroline-based rotaxane 50 by employing the [2 + 2] CA–RE reaction, as shown in Scheme 17 [123]. The initial threading reaction involving the rod molecule 47 and macrocycle 48, constructed using [Cu(MeCN)4]PF6, resulted in the formation of the pseudorotaxane 49. The ensuing [2 + 2] CA–RE reaction of 49

Light-responsive rotaxane-based materials: inducing motion in the solid state

• Adrian Saura-Sanmartin

Beilstein J. Org. Chem. 2023, 19, 873–880, doi:10.3762/bjoc.19.64

• , such as bending, jumping and curling, upon light irradiation. Interestingly, the bending of the crystals could proceed in different directions. As an example, crystals of pseudorotaxane 1a (Figure 1b), having hydrogens as substituents R2 and R3 placed at the ferrocenyl motif and macrocycle

• struts and the photoresponsive linkers. The use of ditopic interlocked building blocks, such as that employed to form mainly a cyclic hetero[4]pseudorotaxane from a self-complementary [2]rotaxane [73], is also envisioned as a strategy that will be employed in the future to dynamically change the

BINOL as a chiral element in mechanically interlocked molecules

• Matthias Krajnc and
• Jochen Niemeyer

Beilstein J. Org. Chem. 2022, 18, 508–523, doi:10.3762/bjoc.18.53

• -workers [46]. They reacted the amine axle 11 with the axially chiral macrocycle (rac)-12 in a mixture of dichloromethane and trifluoroacetic acid in order to generate the pseudorotaxane (rac)-13. Then, an isocyanate stopper was added for the formation of the [2]rotaxane (rac)-14 in a yield of 42%. The X

• mechanical bond, namely from a BINOL-based macrocycle onto the axle. First, they developed [2]rotaxane 27 [52]. Here, the methacrylate-functionalized ammonium salt 25 and the bis-BINOL macrocycle (R,R)-26 give the pseudorotaxane (R,R)-27 through self-assembly. Stoppering of the pseudorotaxane was achieved by

Construction of pillar[4]arene[1]quinone–1,10-dibromodecane pseudorotaxanes in solution and in the solid state

• Xinru Sheng,
• Errui Li and
• Feihe Huang

Beilstein J. Org. Chem. 2020, 16, 2954–2959, doi:10.3762/bjoc.16.245

• reports [44][45]. We found that H and G can be used to build a [3]pseudorotaxane in the solid state but a [2]pseudorotaxane in solution. Results and Discussion Host–guest complexation in the solid state Cocrystals of H and G were obtained by slow evaporation of the solution in methanol. The X-ray

• crystallography revealed that two host molecules complex one guest molecule, forming a [3]pseudorotaxane in the solid state (Figure 1). In the crystal structure, the alkyl chain of the guest is threaded through the cavities of two host molecules, which is stabilized by multiple CH∙∙∙π interactions and hydrogen

• [4]arene[1]quinone molecules, forming a [3]pseudorotaxane in the solid state. However, 1H NMR experiments revealed that the pillar[4]arene[1]quinone encapsulated the guest molecule with a 1:1 stoichiometry to form a [2]pseudorotaxane in solution. One possible reason may be that the interactions

Thermodynamic and electrochemical study of tailor-made crown ethers for redox-switchable (pseudo)rotaxanes

• Henrik Hupatz,
• Marius Gaedke,
• Hendrik V. Schröder,
• Julia Beerhues,
• Arto Valkonen,
• Fabian Klautzsch,
• Sebastian Müller,
• Felix Witte,
• Kari Rissanen,
• Biprajit Sarkar and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2020, 16, 2576–2588, doi:10.3762/bjoc.16.209

• synthesis of crown ether-based rotaxanes in 1995, crown ethers played a crucial role in the development of mechanically interlocked molecules (MIMs) [22][23]. This rotaxane synthesis was facilitated by the formation of a threaded complex (pseudorotaxane) between a secondary ammonium ion and dibenzo-24-crown

• the pseudorotaxane of NDIC8, and thus to a more favorable binding entropy compared to the pseudorotaxane of TTFC8. For TTFC8, the increased binding enthalpy can be explained by additional π–π-interactions between the naphthalene and TTF unit of the crown ether and the ammonium axle, resulting in a

• ·PF6, is not caused by the binding enthalpy ΔH0 (entries 11–14 in Table 1), as one might have expected, assuming the ion pairing to compete with the pseudorotaxane formation. In contrast, the enthalpic contribution is 4–6 kJ/mol less negative with A1·PF6 than in A1·BArF24 complexes, but the formation

Five-component, one-pot synthesis of an electroactive rotaxane comprising a bisferrocene macrocycle

• Natalie Lagesse,
• Luca Pisciottani,
• Maxime Douarre,
• Pascale Godard,
• Brice Kauffmann,
• Vicente Martí-Centelles and
• Nathan D. McClenaghan

Beilstein J. Org. Chem. 2020, 16, 1564–1571, doi:10.3762/bjoc.16.128

• ]rotaxane is a homologue of the versatile benchmark tetraamide variant developed by Leigh and co-workers. The relative templating effect of different hydrogen-bonding motifs in rotaxane and pseudorotaxane generation is compared, with yields varying from 0 to 41%. The electrochemical properties and single

Multiple threading of a triple-calix[6]arene host

• Veronica Iuliano,
• Roberta Ciao,
• Emanuele Vignola,
• Carmen Talotta,
• Patrizia Iannece,
• Margherita De Rosa,
• Annunziata Soriente,
• Carmine Gaeta and
• Placido Neri

Beilstein J. Org. Chem. 2019, 15, 2092–2104, doi:10.3762/bjoc.15.207

• ppm, respectively. The HSQC experiment also correlated the benzylic resonance at 5.10 ppm, attributable to the 1,3,5-trisubstitued benzene-core of 6 in (7+)36 pseudorotaxane, with a carbon resonance at 76.0 ppm. In accord, COSY and HSQC experiments revealed the presence of three principal AX systems

• , DOSY, and ESI-FT-ICR MS/MS experiments. In addition, in the presence of a directional butylbenzylammonium axle, the stereoselective formation of endo-alkyl pseudorotaxane stereoisomers was observed. Experimental HR mass spectra were acquired on a FT-ICR mass spectrometer equipped with a 7T magnet. The

• signals (Na for IS = 2; Nb for guest) and Ma and Mb = molecular masses of IS (a) and complex (b) Sketch of the currently known prototypical examples of handcuff-derived architectures. Chemical drawing of the known bis-calix[6]arene 1 and its handcuff pseudorotaxane architectures 32+ and 52+ previously

Synthesis of a [6]rotaxane with singly threaded γ-cyclodextrins as a single stereoisomer

• Jason Yin Hei Man and
• Ho Yu Au-Yeung

Beilstein J. Org. Chem. 2019, 15, 1829–1837, doi:10.3762/bjoc.15.177

• interlocking at one of the tetra(ethylene glycol) moieties, possibly as a result of the stabilizing interactions between the γ-CD and CB[6]. Indeed, due to the strong interactions between CB[6] and cyclodextrin, it has been reported that CB[6] can dissemble a [3]pseudorotaxane consisting of two linear axles

• bound in the cavity of a γ-CD to form a [4]pseudorotaxane consisting of one γ-CD and two CB[6], and that because of the steric hindrance provided by the CB[6], inclusion of a second guest in the γ-CD cavity is discouraged [46]. The observation that no rotaxane product derived from a 2:1 complex of 1/γ

A heteroditopic macrocycle as organocatalytic nanoreactor for pyrroloacridinone synthesis in water

• Piyali Sarkar,
• Sayan Sarkar and
• Pradyut Ghosh

Beilstein J. Org. Chem. 2019, 15, 1505–1514, doi:10.3762/bjoc.15.152

• supramolecular assemblies like molecular rotors (pseudorotaxane, rotaxane, catenane), molecular switches, molecular shuttles, etc. [32][33][34][35][36][37][38][39][40][41][42][43]. Furthermore, macrocycles have been applied in the area of ion–ion pair recognition and heterometallic complex formation [44][45][46

Fabrication, characterization and adsorption properties of cucurbit[7]uril-functionalized polycaprolactone electrospun nanofibrous membranes

• Changzhong Chen,
• Fengbo Liu,
• Xiongzhi Zhang,
• Zhiyong Zhao and
• Simin Liu

Beilstein J. Org. Chem. 2019, 15, 992–999, doi:10.3762/bjoc.15.97

• within the PCL/CB[7] nanofibers without forming PCL/CB[7] ICs or PCL/CB[7] pseudorotaxane. Another interesting observation is that the intensity of all the diffraction peaks for PCL/CB[7] nanofibers increases with the increase of CB[7] content. The phenomenon may be caused by a variation of the

• temperatures (at around 41 °C). Tonelli et al. reported PCL/PCL-α-CD-IC nanofibers [17] and PCL/α-CD pseudorotaxane nanofibers [12] obtained by electrospinning. They found that the variations of phase-transition temperatures of nanofibers compared with those of neat PCL a) both, Tm and Tc of PCL/PCL-α-CD-IC

• nanofibers increased, b) Tm of PCL/α-CD pseudorotaxane nanofibers was almost the same and their Tc increased, and c) Tm of uncomplexed PCL/40% α-CD composite nanofibers decreased and their Tc increased. Apparently, the change tendency of Tm and Tc of the PCL/CB[7] nanofibers reported in this work matches

Mechanochemistry of supramolecules

• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2019, 15, 881–900, doi:10.3762/bjoc.15.86

• applied a Diels–Alder reaction of 1,2,4,5-tetrazine with a terminal alkyne unit in a 21-crown-7-based [2]pseudorotaxane 14. The [2]rotaxane 15 was produced in 81% yield having pyridazine groups as stoppers (Figure 7). Very recently, Nierengarten and co-workers reported a solvent-free mechanochemical

• synthesis of pillar[5]arene-containing [2]rotaxanes (Figure 8). Mixing a 2:1 ratio of pillar[5]arene (wheel) with dodecanedioyl dichloride (axle) in CHCl3 resulted in the formation of pseudorotaxane 16 which was further treated with different amines (stopper) in a stainless-steel jar with 4 steel balls

• of the rotaxane system via pseudorotaxane 18. A shorter reaction time, use of small amounts of solvent and the high yield were the advantages over the solvent-mediated synthesis [62]. Macrocycle synthesis The mechanochemical synthesis of sphere-like nanostructures was reported by Severin and co

Synthesis of a water-soluble 2,2′-biphen[4]arene and its efficient complexation and sensitive fluorescence enhancement towards palmatine and berberine

• Xiayang Huang,
• Xinghua Zhang,
• Tianxin Qian,
• Junwei Ma,
• Lei Cui and
• Chunju Li

Beilstein J. Org. Chem. 2018, 14, 2236–2241, doi:10.3762/bjoc.14.198

• compared with the free guest. Especially, the chemical shifts for the middle protons, H1–6, and H10–11, are larger than those for the ending H7–9. These results indicate that berberine was engulfed by the cavity of 2,2’-CBP4 to form a pseudorotaxane-type inclusion complex. Similar complexation-induced NMR

Tetrathiafulvalene – a redox-switchable building block to control motion in mechanically interlocked molecules

• Hendrik V. Schröder and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2018, 14, 2163–2185, doi:10.3762/bjoc.14.190

• to rotaxanes is that the axle does not have bulky stopper groups that prevent the deslipping of the wheel. Thus, a pseudorotaxane forms by non-covalent interactions between host and guest without a mechanical bond. Pseudorotaxanes are important precursors of MIMs from which the construction of

• rotaxanes is achieved by stoppering reactions, while catenanes can be made by macrocyclization of the pseudorotaxane thread. Therefore, we discuss in the following section reports of important pseudorotaxanes and inclusion complexes that contributed to major developments of TTF-based MIMs and AMMs. The

• first TTF-based pseudorotaxane was reported by Stoddart and Williams in 1991 (Figure 5) [33]. At this time, they investigated the host–guest properties of the π-electron-poor cyclophane cyclobis(paraquat-p-phenylene) (3) in form of the tetrakis(hexafluorophosphate) salt [58]. The square-shaped host

Calix[6]arene-based atropoisomeric pseudo[2]rotaxanes

• Carmine Gaeta,
• Carmen Talotta and
• Placido Neri

Beilstein J. Org. Chem. 2018, 14, 2112–2124, doi:10.3762/bjoc.14.186

• axle. In all the examined cases, the 1,2,3-alternate and cone atropoisomers are, respectively, the kinetic and the thermodynamic ones. Keywords: atropoisomers; calixarene; conformation; pseudorotaxane; social isomerism; Introduction Mechanomolecules [1][2][3][4], such as rotaxanes and catenanes show

• I*, Figure 1) consisting of achiral components. The combination of a macrocycle with rotational asymmetry and a directional thread with non-equivalent ends is the cause of chirality in this example (Figure 1). Interestingly, our group showed that a chiral pseudorotaxane can be generated upon

• pseudorotaxane architectures [32][33], where it usually adopts a cone conformation. The examples reported by us [33][34][35][36][37][38] (Figure 4b) and by Arduini [32][39] (Figure 4a) showed that the directionality of the calixarene wheel in the cone conformation plays a pivotal role in the formation of

A pyridinium/anilinium [2]catenane that operates as an acid–base driven optical switch

• Sarah J. Vella and
• Stephen J. Loeb

Beilstein J. Org. Chem. 2018, 14, 1908–1916, doi:10.3762/bjoc.14.165

• as shown from 3 [21]. Once the precursor components were synthesized, the [2]catenane was assembled in two steps. Firstly, [5][OTf]2 was reacted with ten equivalents of the bis(bromomethyl)terphenyl linker 6 in CH3CN to afford [7][OTf]4 in moderate yield. Secondly, the [2]pseudorotaxane [7DB24C8]4

• ]+ calcd, 1457.1114; found, 1457.1144. Synthesis of [8DB24C8][OTf]6 [7][OTf]4 (0.155 g, 0.0963 mmol) and DB24C8 (0.432 g, 0.963 mmol) were dissolved in a two phase CH3NO2/H2O mixture and stirred at room temperature for 30 min to allow [2]pseudorotaxane formation. Compound 4 (0.0330 g, 0.0963 mmol) was then

Efficient catenane synthesis by cucurbit[6]uril-mediated azide–alkyne cycloaddition

• Antony Wing Hung Ng,
• Chi-Chung Yee,
• Kai Wang and
• Ho Yu Au-Yeung

Beilstein J. Org. Chem. 2018, 14, 1846–1853, doi:10.3762/bjoc.14.158

• mixture contained the [3]catenane Cat-1 as the major product with >85% yield (Scheme 2). Using DN-CC to first form the pseudo[3]rotaxane CB[6] complex did not affect the efficiency of CBAAC and Cat-1 was obtained in a similar yield. These results show that the initial formation of the pseudorotaxane

Structural diversity in the host–guest complexes of the antifolate pemetrexed with native cyclodextrins: gas phase, solution and solid state studies

• Magdalena Ceborska,
• Magdalena Zimnicka,
• Aneta Aniela Kowalska,
• Kajetan Dąbrowa and
• Barbara Repeć

Beilstein J. Org. Chem. 2017, 13, 2252–2263, doi:10.3762/bjoc.13.222

• complex with α-CD and pseudorotaxane inclusion-type complexes with β-, and γ-CDs. UV–vis titrations at pH 7.4 gave association constants for the obtained complexes. The stability of the complexes increases in the series: α-CD/PTX < γ-CD/PTX << β-CD/PTX. The association of PTX with a monomer cyclodextrin

• complexes in which a FA guest is trapped in the central cavity of CD in a form of pseudorotaxane structure are supposed to be substantially more stable than complexes with a ligand being associated with the CD’s surface or partially allied with CD’s internal space. In the solid state two complementary

• energies, are these resulting from covalent bond cleavages [19]. The loosely bonded CDs/PTX complexes therefore correspond to a pseudorotaxane inclusion complex in which PTX is threaded through the CD’s cavity or other type of exclusion aggregate. To distinguish between these two types of complexes their

Self-assemblies of γ-CDs with pentablock copolymers PMA-PPO-PEO-PPO-PMA and endcapping via atom transfer radical polymerization of 2-methacryloyloxyethyl phosphorylcholine

• Jing Lin,
• Tao Kong,
• Lin Ye,
• Ai-ying Zhang and
• Zeng-guo Feng

Beilstein J. Org. Chem. 2015, 11, 2267–2277, doi:10.3762/bjoc.11.247

• -chain-stranded; pentablock copolymer; poly(pseudorotaxane); polyrotaxane; single-chain-stranded; Introduction Cyclodextrins (CDs) are a series of macrocyclic molecules composed of 6, 7, or 8 (α-, β-, and γ-CD, respectively) glucopyranose units. Their hydrophilic surface and hydrophobic inner cavity

Discrete multiporphyrin pseudorotaxane assemblies from di- and tetravalent porphyrin building blocks

• Mirko Lohse,
• Larissa K. S. von Krbek,
• Sebastian Radunz,
• Suresh Moorthy,
• Christoph A. Schalley and
• Stefan Hecht

Beilstein J. Org. Chem. 2015, 11, 748–762, doi:10.3762/bjoc.11.85

• . The crown ether/secondary ammonium ion binding motif [34] is a powerful tool to create well-defined pseudorotaxane structures [35][36][37][38][39], which have also served as precursors in rotaxane syntheses [40][41][42] thus providing access to interlocked, mechanically bound molecules. Based on these

• desired doubly, respectively quadruply charged pseudorotaxane ([A2@C12]2+ at m/z 1094 and [A4@C14]4+ at m/z = 898). In addition, a second set of signals for the triply, respectively five-fold charged species ([A2@C12 + H]3+ at m/z = 729 and [A4@C14 + H]5+ at m/z = 719) could be observed. The most abundant

• = 773). This can be easily explained with the nature of the ESI spray process, which is known to cause the dissociation in multiply charged non-covalently bound complexes. The results of the NMR titrations, however, clearly indicate the doubly bound pseudorotaxane A12@C2 to be the most prominent species

First principle investigation of the linker length effects on the thermodynamics of divalent pseudorotaxanes

• Andreas J. Achazi,
• Doreen Mollenhauer and
• Beate Paulus

Beilstein J. Org. Chem. 2015, 11, 687–692, doi:10.3762/bjoc.11.78

• pseudorotaxanes the absolute agreement between the calculated and the experimentally determined Gibbs energies is not as good as in the case of monovalent binding, but the same trends are observed in the simulations as in experiment. The divalent pseudorotaxane with the n0 linker shows a significantly stronger

• is 6.5 kJ/mol lower than that of the unfolded form. Conclusion The Gibbs energies of association, including enthalpic and entropic temperature effects, solvent effects and the counter ions, have been determined for the divalent crown-8/ammonium pseudorotaxane with different linkers in the guest

Synthesis of an organic-soluble π-conjugated [3]rotaxane via rotation of glucopyranose units in permethylated β-cyclodextrin

• Jun Terao,
• Yohei Konoshima,
• Akitoshi Matono,
• Hiroshi Masai,
• Tetsuaki Fujihara and
• Yasushi Tsuji

Beilstein J. Org. Chem. 2014, 10, 2800–2808, doi:10.3762/bjoc.10.297

• CD [11], and (III) copolymerization of the thus-formed pseudorotaxane with linker molecules [12]. These polymers are soluble in water but generally insoluble in organic solvents; this is because the hydrophilic CD covers the organic soluble π-conjugated polymer chains [13]. Uncovered sites are also

Substitution effect and effect of axle’s flexibility at (pseudo-)rotaxanes

• Friedrich Malberg,
• Jan Gerit Brandenburg,
• Werner Reckien,
• Oldamur Hollóczki,
• Stefan Grimme and
• Barbara Kirchner

Beilstein J. Org. Chem. 2014, 10, 1299–1307, doi:10.3762/bjoc.10.131

• Figure 2). Distances in parentheses denote the corresponding length to the heavy (non-hydrogen) atom. Interaction energies Eint for the different pseudorotaxane systems, labeling see Figure 1. The first two columns list the substituents succeeded by their effects (mesomeric or inductive). The last line

• gives the values for the di-phenyl structures. In the last column, the Hammett-parameters are given. Hydrogen bond distances in Å for the different pseudorotaxane systems, for labeling see Figure 2. The second and third last lines show the substitution at the meta-position. Interaction energies Eint for

• the different pseudorotaxane systems applying a solvent model, labeling see Figure 1. The first two columns list the substituents succeeded by their effects (mesomeric or inductive) as in Table 2. Hydrogen bond geometry in Å for the different pseudorotaxane systems with solvent model, labeling see

Control over molecular motion using the cis–trans photoisomerization of the azo group

• Estíbaliz Merino and
• María Ribagorda

Beilstein J. Org. Chem. 2012, 8, 1071–1090, doi:10.3762/bjoc.8.119

• gold electrode [109]. In 2003, a molecular machine based on a pseudorotaxane was described [110]. Assembly between 7 and 8 occurs only when the azobenzene 7 adopts the cis configuration. The pseudorotaxane 7+8 is disassembled into its two components when the isomerization to trans-azobenzene occurs by

• guanidinium ion by a cis,cis-bis-azo derivative 3. Recognition of cesium ions by cis-azo derivative 4. Photocontrolled formation of an inclusion complex of cyclodextrin trans-azo 5+6. Pseudorotaxane-based molecular machine. Molecular hinge. Reprinted (adapted) with permission from Org. Lett. 2004, 6, 2595

Synthesis of multivalent host and guest molecules for the construction of multithreaded diamide pseudorotaxanes

• Nora L. Löw,
• Egor V. Dzyuba,
• Boris Brusilowskij,
• Lena Kaufmann,
• Elisa Franzmann,
• Wolfgang Maison,
• Emily Brandt,
• Daniel Aicher,
• Arno Wiehe and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2012, 8, 234–245, doi:10.3762/bjoc.8.24

• polar aprotic solvent, such as acetone, acetonitrile, DMF or DMSO, which would solubilize the axles sufficiently well, would interfere strongly with pseudorotaxane formation. The tertiary amides are much more soluble and, therefore, appear to be the more appropriate binding site. However, the better

• 1H NMR spectra of 1:1 mixtures of axles and wheels, structure-indicative signal shifts are observed that demonstrate the axles to be threaded through the wheels (Figure 2). Consequently, the binding event cannot easily be quantified, but there is qualitative evidence for pseudorotaxane formation

• this approach. With our toolbox, the number and position of binding sites can be varied systematically; hence, the toolbox provides a means to examine multivalency. However, despite the fact that there is qualitative evidence for pseudorotaxane formation, the binding motif is not yet optimal for a

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

• secondary ammonium ion slips through the crown ether ring forming “pseudorotaxane” like structures (Figure 5). The structural variability of crown ethers is very large. This allows varying the ring size, introducing substituents and changing the donor sites from oxygen atoms, to nitrogen (azacrowns) or