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

• wormlike nanoparticles. In rotaxanes, the utilization of metal–ligand bonding involving CuI is a common strategy for immobilizing a thread moiety within a macrocycle. However, the efficacy of such a bonding is compromised when catalysts are used in stoppering reactions, e.g., the copper-catalyzed azide

Active-metal template clipping synthesis of novel [2]rotaxanes

• Cătălin C. Anghel,
• Teodor A. Cucuiet,
• Niculina D. Hădade and
• Ion Grosu

Beilstein J. Org. Chem. 2023, 19, 1776–1784, doi:10.3762/bjoc.19.130

• beautiful structures and intriguing properties. We present herein a new synthetic strategy to access [2]rotaxanes, namely active-metal template clipping. We discuss the design of the target [2]rotaxanes, synthesis and characterization of the axle, macrocycle precursors and macrocycles as well as preparation

• of the final [2]rotaxanes by active template copper(I)-catalyzed alkyne–azide cycloaddition (CuAAC) as key step of the synthesis. HRMS and NMR experiments have been performed to confirm the formation of the interlocked structures. Keywords: active-metal template; clipping; copper(I)-catalyzed alkyne

• –azide cycloaddition; mechanically interlocked structures; [2]rotaxanes; Introduction Since its birth, in the late sixties [1][2][3], the field of mechanically interlocked molecules (MIMs), including rotaxanes, has gained significant attention culminating by recognition with a Nobel prize in Chemistry

Tying a knot between crown ethers and porphyrins

• Maksym Matviyishyn and
• Bartosz Szyszko

Beilstein J. Org. Chem. 2023, 19, 1630–1650, doi:10.3762/bjoc.19.120

• supramolecular architectures [45], e.g., catenanes [73], rotaxanes [74], and catalytic systems [75]. Pelegrino and co-workers reported on crowned porphyrinoids demonstrating interesting photophysical properties [71]. The crown ether part was also demonstrated to play a role of a linker between two porphyrin

• molecules, e.g., catenanes and rotaxanes (Figure 16C). The formation of such compounds would eventually result in the formation of a unique group of three-dimensional ligands with co-existing porphyrin-like and crown ether cavities. The perspective article has highlighted the wide range of crown ether

Cyclodextrins as building blocks for new materials

• Miriana Kfoury and
• Sophie Fourmentin

Beilstein J. Org. Chem. 2023, 19, 889–891, doi:10.3762/bjoc.19.66

• science that require high performance with minimal environmental impact. They are involved in the construction of interlocked molecules (rotaxanes and catenanes), supramolecular polymers, artificial enzymes, hydrogels, metal–organic frameworks, supramolecular solvents, fibers, nanotubes, nanoparticles

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

• -responsive materials; mechanical bond; mechanically interlocked materials; rotaxanes; Introduction Light turns out to be a suitable and tailorable stimulus in order to develop materials showing improved functionalities, such as those of smart materials [1][2][3][4][5]. The characteristics of light which

• scaffolds [11]. In particular, rotaxanes and pseudorotaxanes have led to a greater number of applications due to their inherent dynamics and the switching possibility through a rational design [12]. Thus, rotaxane-based materials have attracted the interest of the scientific community due to their enhanced

• properties and functionalities [13][14][15][16][17]. Although great strides have been made in the development of photoresponsive rotaxanes [18][19][20][21][22][23][24][25][26][27][28][29], progress on interlocked materials working via photoirradiation is less abundant in the literature. However

Supramolecular approaches to mediate chemical reactivity

• Pablo Ballester,
• Qi-Qiang Wang and
• Carmine Gaeta

Beilstein J. Org. Chem. 2022, 18, 1463–1465, doi:10.3762/bjoc.18.152

• rotaxanes. MIMs show interesting structural and topological features and offer conceptually new possibilities as catalysts. In their minireview, Krajnc and Niemeyer [21] highlighted the use of the axially chiral 1,1'-binaphthyl-2,2'-diol (BINOL) unit as a stereogenic element in MIMs. The authors comment on

Cyclodextrin-based Schiff base pro-fragrances: Synthesis and release studies

• Attila Palágyi,
• Jindřich Jindřich,
• Juraj Dian and
• Sophie Fourmentin

Beilstein J. Org. Chem. 2022, 18, 1346–1354, doi:10.3762/bjoc.18.140

• hydrolysis, oxidation, or light (Figure 1) [18]. Different substrates were used to synthesize pro-fragrances, like polymers [19], ionic liquids [20], rotaxanes [21], or saccharides [22]. To the best of our knowledge, no studies investigate the use of CDs as substrate. Linking the fragrance to CDs could

Heteroleptic metallosupramolecular aggregates/complexation for supramolecular catalysis

• Prodip Howlader and
• Michael Schmittel

Beilstein J. Org. Chem. 2022, 18, 597–630, doi:10.3762/bjoc.18.62

• complex [FeCu2(104)2]4+ (Figure 23), the latter controlling a double-click catalytic access to rotaxanes 109, by addition/removal of iron(II) ions [110]. Although [FeCu2(104)2]4+ is an open and flexible structure, the availability of two catalytic copper(I) centers positioned at 34 Å in the transition

• preparation of rotaxanes, the exploitation of cooperative and strain effects in double-click strategies is a promising strategy. A completely different approach to switchable supramolecular catalysis made use of a supramolecular cage-to-device transformation under dissipative conditions (Figure 24) [112

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

• ; interlocked molecules; rotaxanes; Introduction In the last decades the synthesis and application of mechanically interlocked molecules (MIMs), such as catenanes and rotaxanes, has gained more and more attention [1][2][3][4]. MIMs offer conceptually new possibilities through their unique structure, with

• rotaxanes, the helicity is predetermined by the planar chirality (based on the underlying macrocycle–macrocycle interactions), so that only two diastereoisomers remain for a given BINOL configuration (e.g., (R)-(Rp) and (R)-(Sp) in case of (R)-BINOL). In contrast to the axial chirality of the BINOL unit

•  6a). Subsequently, Takata and co-workers presented a highly diastereoselective synthesis of [2]rotaxane amine N-oxides via intercomponent chirality transfer (see Figure 6b) [53]. For the synthesis of the rotaxanes, complexes of hydroxy-terminated ammonium salts 28a–d and BINOL-based macrocycle (R)-12

Trichloroacetic acid fueled practical amine purifications

• Aleena Thomas,
• Baptiste Gasch,
• Enzo Olivieri and
• Adrien Quintard

Beilstein J. Org. Chem. 2022, 18, 225–231, doi:10.3762/bjoc.18.26

• from rotaxanes, cucurbit[8]uril, to supramolecular smart materials [11][12][13][14][15][16]. TCA is also known for its application in the precipitation of proteins through what is believed to be an unfolding of the proteins structures [17][18]. In this context, we hypothesized that TCA could be used to

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

• the further capping of the pseudorotaxanes to construct rotaxanes. Keywords: host–guest chemistry; pillar[4]arene[1]quinones; pillararenes; pseudorotaxanes; supramolecular chemistry; Introduction Relying on the research of basic science, supramolecular chemistry has become an important mean for

• , including molecular switches, molecular logic gates, molecular machines, supramolecular polymers, etc. [6][7][8][9][10][11]. Pseudorotaxanes not only are used as the supramolecular precursors for the synthesis of rotaxanes and catenanes but also play an important role in the construction of supramolecular

• pseudorotaxanes to construct rotaxanes, which will broaden the range of potential applications of pillararene derivatives for the manufacture of sophisticated supramolecular architectures and functional supramolecular systems. Crystal structures of the [3]pseudorotaxane composed of H and G in the solid state

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

• described with regard to their potential to form redox-switchable rotaxanes. A combination of isothermal titration calorimetry and voltammetric techniques reveals correlations between the binding energies and redox-switching properties of the corresponding pseudorotaxanes with secondary ammonium ions. For

• ; redox chemistry; rotaxanes; supramolecular chemistry; Introduction Pedersen discovered crown ethers in 1967 while searching for multidentate ligands for the vanadyl group [1][2][3]. He was later awarded the Nobel Prize in Chemistry for his studies on the crown ether selective binding properties towards

• 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

Design and synthesis of a bis-macrocyclic host and guests as building blocks for small molecular knots

• Elizabeth A. Margolis,
• Rebecca J. Keyes,
• Stephen D. Lockey IV and
• Edward E. Fenlon

Beilstein J. Org. Chem. 2020, 16, 2314–2321, doi:10.3762/bjoc.16.192

• Sauvage, Stoddart, and Feringa for their work on molecular machines [4]. Sauvage [5] and Stoddart [6] extensively used macrocycles in their ground-breaking work on catenanes, rotaxanes, knots, and other topologically novel compounds. Exciting advances in the field of molecular topology continue with novel

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

• to perform several functions as artificial molecular switches [1]. The template-directed synthesis of such sophisticated catenane and rotaxane molecular architectures allowed the expansion of chemical diversity and properties. Among these architectures, electroactive rotaxanes have been described to

• prove a valuable component for the construction of novel redox-active supramolecular systems, such as rotaxanes with strongly binding H-bonding templating sites, or indeed juxtaposed into existing functional architectures and benchmark variants. Results and Discussion Synthesis Our first approach to the

• structure 2025 conformers were examined (see text) and the obtained conformers were ordered by relative energy to obtain the most stable one. (a) Non-functionalized rotaxanes previously described in the literature. (b) The redox-active rotaxane developed in this work. Synthesis of the redox-active rotaxanes

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• groups due to the anion binding, including chloride and other oxoanion salts. They also proved that the anions binding strength falls in line with their basicity as seen in the series AcO− > H2PO4− > Cl− > SO42− >NO3−. 2.5. 1,2,3-Triazolium macrocycles and [2]rotaxanes Supramolecular interactions could

• (chalcogen = Se, Te) motif as a novel ChB donor for anion binding. By exploiting the possibility of the chalcogen atoms to orient within the macrocycle cavity to chelate the copper(I) endotopically, the first examples of mechanically interlocked [2]rotaxanes containing ChB donor groups has been prepared via

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

• ]. Among the self-assembly processes, those that lead to the formation of interlocked and/or interpenetrated supramolecular structures have inspired many scientists [5][6][7][8]. The synthesis of interlocked molecules such as rotaxanes, catenanes, and high-order architectures (e.g., polyrotaxanes, suitanes

• , daisy-chain pseudorotaxanes, olympiadane, Janus rotaxanes [5]) is generally obtained through a template-approach [9] exploiting the threading process between linear (axle) and macrocyclic (wheel) components. In order to synthesize high-order interpenetrated architectures, much attention has been

• alkylammonium cations, as TFPB− salts, inside the aromatic cavity of calixarene [20] and dihomooxacalixarene hosts [21][22]. Thus, through this ‘superweak anion’ approach, we have synthesized interesting examples of calixarene/ammonium-based interlocked structures such as calix-rotaxanes [23][24] and calix

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

• Jason Yin Hei Man Ho Yu Au-Yeung Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China 10.3762/bjoc.15.177 Abstract A series of hetero [4]-, [5]- and [6]rotaxanes containing both cucurbit[6]uril (CB[6]) and γ-cyclodextrin (γ-CD) as the macrocyclic components

• have been synthesized via a threading-followed-by-stoppering approach. Due to the orthogonal binding of CB[6] to ammonium and γ-CD to biphenylene/tetra(ethylene glycol), the [n]rotaxanes display a specific sequence of the interlocked macrocycles. In addition, despite of the asymmetry of γ-CD with

• building blocks for the construction of complex molecular topology such as rotaxanes and catenanes [12][13][14][15]. For example, by making use of hydrophobic-driven binding of simple alkyl groups in water to α-CD, Ogino has reported one first example of a rotaxane assembly featuring an alkyldiamine

Understanding the unexpected effect of frequency on the kinetics of a covalent reaction under ball-milling conditions

• Ana M. Belenguer,
• Adam A. L. Michalchuk,
• Giulio I. Lampronti and
• Jeremy K. M. Sanders

Beilstein J. Org. Chem. 2019, 15, 1226–1235, doi:10.3762/bjoc.15.120

• for a wide range of different syntheses and chemical reactions of inorganic [8][9] and organic [10][11] compounds. Even supramolecular architectures such as co-crystals and metal-organic frameworks [4][12][13][14], cages [15] and rotaxanes [16] could be formed mechanochemically. Crucially, the

Molecular recognition using tetralactam macrocycles with parallel aromatic sidewalls

• Dong-Hao Li and
• Bradley D. Smith

Beilstein J. Org. Chem. 2019, 15, 1086–1095, doi:10.3762/bjoc.15.105

• ] macrocycle and a larger amount of the corresponding [2]catenane. Subsequent work found that conducting the reaction in the presence of a dumbbell-shaped template was a general way to make a wide range of [2]rotaxanes [28]. Listed in Scheme 2 are the yields of [2]rotaxane produced using various biscarbonyl

• acene guests Rotaxane template 18 in Scheme 2 is a squaraine dye whose central core has two oxygen atoms that can form hydrogen bonds with the tetralactam NH residues. Squaraine rotaxanes were first prepared by the Smith group in 2005 using the Leigh-type clipping method [44]. As a general trend the

• conformations is an outward directed NH residue. Solution-state NMR data suggests that the surrounding tetralactam in these [2]rotaxanes undergoes rapid exchange between these different conformations, a dynamic process that has been called macrcocyle breathing, and that there is also simultaneous co

Mechanochemistry of supramolecules

• Anima Bose and
• Prasenjit Mal

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

• acetic acid (for liquid-assisted grinding, LAG) led to the regioselective C–H activation (Figure 5) [58]. In 2008, the mechanochemical synthesis of both [2]- and [4]rotaxanes was reported by Chiu and co-workers. The reactions led to high yields of the products 12 and 13 under solvent-free conditions at a

• 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

• –acceptor [2]rotaxanes such as 19 through liquid-assisted mechanochemical milling (Figure 9). The donor–acceptor interaction between the electron-deficient naphthalene diimide moiety and the electron-rich naphthalene moieties embedded in the macrocyclic polyethers played the vital role for the construction

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

• MIMs and their applications. A brief historical overview and a selection of important examples from the past until now are given. Furthermore, we will highlight our latest research on TTF-based rotaxanes. Keywords: artificial molecular machines; mechanically interlocked molecules; molecular switches

• [9] "for the design and synthesis of molecular machines" is an outstanding appreciation of the public and scientific community. Mechanically interlocked molecules (MIMs) such as rotaxanes [10] or catenanes [11] are ideally suited for the construction of AMMs. In comparison to covalently linked

• 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

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

• interesting properties as nanodevices for catalysis [5][6][7][8], recognition, and sensing [9][10][11][12][13]. Beyond these ascertained potentialities, interpenetrated architectures show fascinating structures that still stimulate the imagination of scientists. An amazing aspect of rotaxanes and catenanes is

• stereoisomeric directional pseudo[2]rotaxanes, rotaxanes, and catenanes. Also in this case [38], we were able to obtain a stereoselective threading of the cone calix[6]arene-wheel with alkylbenzylammonium axles (Figure 4b), in which the endo-alkyl pseudo[2]rotaxane stereoisomer was the favoured one [38]. The

A switchable [2]rotaxane with two active alkenyl groups

• Xiu-Li Zheng,
• Rong-Rong Tao,
• Rui-Rui Gu,
• Wen-Zhi Wang and
• Da-Hui Qu

Beilstein J. Org. Chem. 2018, 14, 2074–2081, doi:10.3762/bjoc.14.181

• , which act as important precursors for constructing stimuli-responsive supramolecular materials [21][22]. Rotaxanes [23][24][25][26][27][28][29][30][31], as one of the most important MIMs, have been deeply investigated because of their excellent properties and convenient synthesis. By introducing various

• functional groups, such kind of MIMs has been used to construct stimuli-responsive materials, which diversified and improved the functions of traditional polymers. Up to now, the repertoire of available functional rotaxanes as building blocks for the fabrication of stimuli-responsive polymers remains limited

• because of the fact that the induction of active and functional groups make the preparation of rotaxanes more difficult and complicated. Therefore, it is urgent to enrich both the family of stimuli-responsive units and the methods for constructing this kind of smart materials. In this paper, we report the

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

• derivatize, [2]rotaxanes are deemed easier to fine-tune from a structural perspective than [2]catenanes. Although we were able to create an optically sensitive [2]catenane molecular shuttle with the bis(pyridinium)ethane and benzylanilinium recognition motifs, we could not achieve the true ON/OFF, bistable

• molecular switching previously observed for analogous [2]rotaxanes. Experimental General comments 4-Bromobenzyl bromide, 4-bromoaniline, 4-pyridylboronic acid, 1,3-dichlorobenzene, p-tolylmagnesium bromide, n-butyllithium and N-bromosuccinimide were purchased from Aldrich and used as received. Benzoyl

Synthesis of diamido-bridged bis-pillar[5]arenes and tris-pillar[5]arenes for construction of unique [1]rotaxanes and bis-[1]rotaxanes

• Ying Han,
• Li-Ming Xu,
• Cui-Yun Nie,
• Shuo Jiang,
• Jing Sun and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2018, 14, 1660–1667, doi:10.3762/bjoc.14.142

• afforded diamido-bridged bis-pillar[5]arenes. 1H NMR and 2D NOESY spectra clearly indicated that [1]rotaxanes were formed by insertion of longer diaminoalkylene unit into the cavity of one pillar[5]arene with another pillar[5]arene acting as a stopper. The similar catalysed amidation reaction of pillar[5

• ]arene di(oxybutoxy)benzoic acid with monoamido-functionalized pillar[5]arenes resulted in the diamido-bridged tris-pillar[5]arenes, which successfully form the unique bis-[1]rotaxanes bearing longer than diaminopropylene diamido bridges. Keywords: bis-[1]rotaxane; mechanically interlocked molecule

• axle to prevent dissociation of the subcomponents. In recent years, many effects have been devoted to the construction and functionalization of pseudo[1]rotaxanes and [1]rotaxanes [11][12][13][14][15][16][17][18][19][20]. For this purpose, the well-known macrocycles such as crown ether [21][22][23