Planar Chiral Rotaxanes Research Articles

Research progress in mechanically planar chiral rotaxanes

Research progress in mechanically planar chiral rotaxanes

Catalytic Enantioselective Synthesis of Inherently Chiral Molecules: Recent Advances

AbstractInherent chirality represents a distinct category of molecular chirality that does not fall within the traditional classification of four chiral elements: central, axial, planar, and helical chirality. While extensive research has been conducted on the catalytic enantioselective construction of these conventional chiralities, the corresponding synthesis of inherently chiral molecules has remained largely unexplored. This minireview provides a comprehensive summary of recent advancements in this field, focusing on the catalytic asymmetric synthesis of inherently chiral calixarenes, saddle‐shaped tetraphenylenes and their heterocycle derivatives, mechanically planar chiral rotaxanes and chiral multilayer 3D frameworks, as well as our perspective in this field.

A chiral macrocycle for the stereoselective synthesis of mechanically planar chiral rotaxanes and catenanes

A chiral macrocycle for the stereoselective synthesis of mechanically planar chiral rotaxanes and catenanes

Post‐Mechanical Bond Formation Desymmetrization Approach to Obtain Mechanically Planar Chiral Rotaxanes

AbstractThe preparation of chiral mechanically interlocked molecules has experienced a great development in the last decade, showing a wide range of applications, including catalysis and molecular machinery. New types of chirality have emerged as a consequence of the mechanical bond, such as mechanically planar chirality, which can exist even when both components are achiral. The mechanically planar chirality in such interlocked structures is usually created during the assembly of the rotaxane architecture. Recently, Tian, Zhu and coworkers decoupled the creation of mechanically planar chirality and assembly of the mechanical bond by using a desymmetrizing Suzuki‐Miyaura reaction of a series of mechanically prochiral rotaxanes. This strategy afforded the target chiral interlocked products showing up to 96.5 : 3.5 enantiomeric ratio.

Catalytic desymmetrization of the mechanical bond

In the October issue of Chem , Chong Tian, Ye Zhu, and co-workers describe a post-synthetic catalyst-controlled desymmetrization strategy for synthesizing mechanically planar chiral rotaxanes by relying on distal ionic interactions between a prochiral rotaxane and a novel anionic chiral phosphine ligand to trigger a desymmetrizing Pd-catalyzed Suzuki-Miyaura coupling. In the October issue of Chem , Chong Tian, Ye Zhu, and co-workers describe a post-synthetic catalyst-controlled desymmetrization strategy for synthesizing mechanically planar chiral rotaxanes by relying on distal ionic interactions between a prochiral rotaxane and a novel anionic chiral phosphine ligand to trigger a desymmetrizing Pd-catalyzed Suzuki-Miyaura coupling.

Mechanically planar chiral rotaxanes through catalytic desymmetrization

<h2>Summary</h2> Establishing mechanical chirality has remained a substantial synthetic hurdle despite the fast-growing applications of interlocked architectures in supramolecular chemistry. Here, we report the development of a catalyst-controlled desymmetrization strategy that decouples the creation of mechanically planar chirality and assembly of interlocked bonds. Employing a novel class of anionic chiral phosphine ligands, the Pd-catalyzed Suzuki-Miyaura reactions enable enantioselective access to various mechanically planar chiral rotaxanes. This study demonstrates that precise catalytic stereocontrol over mechanical chirality is achievable by engaging distal ionic substrate-catalyst interactions, despite the noncovalent nature of the interlocking stereogenic elements.

Progress on synthesis of optically pure mechanical planar chiral rotaxanes and planar chiral macrocycle molecules

近年来，面手性逐渐引起了多个领域科学家的关注。面手性结构单元广泛存在于多种活性天然产物和药物分子中，如机械平面手性轮烷和平面手性大环化合物。这两类结构在分子机器、分子识别、不对称催化以及药物研发等多个领域展示出了重要应用价值。然而，由于机械平面手性轮烷和平面手性大环化合物的结构复杂性，合成这两类化合物仍然面临着较大挑战，且合成方法相对较少。因此，研究高效制备上述两类面手性化合物的新策略是非常有价值的研究方向。目前合成化学家已发展了手性色谱分离技术、手性源诱导、过渡金属或酶催化的不对称环化反应等制备面手性化合物的策略。本文综述了制备光学纯机械面手性轮烷和面手性大环两类结构的研究进展，旨在启发从事相关领域的合成化学家发展更多高效合成面手性结构的新策略，从而为高效构筑机械平面手性轮烷化合物和平面手性大环化合物提供借鉴。

A Chiral Macrocycle for the Synthesis of Both Mechanically Planar Chiral Rotaxanes and Catenanes in Excellent Enantiopurity

A Chiral Macrocycle for the Synthesis of Both Mechanically Planar Chiral Rotaxanes and Catenanes in Excellent Enantiopurity

A chiral interlocking auxiliary strategy for the synthesis of mechanically planar chiral rotaxanes.

Rotaxanes can display molecular chirality solely due to the mechanical bond between the axle and encircling macrocycle without the presence of covalent stereogenic units. However, the synthesis of such molecules remains challenging. We have discovered a combination of reaction partners that function as a chiral interlocking auxiliary to both orientate a macrocycle and, effectively, load it onto a new axle. Here we use these substrates to demonstrate the potential of a chiral interlocking auxiliary strategy for the synthesis of mechanically planar chiral rotaxanes by producing a range of examples in high enantiopurity (93–99% e.e.), including so-called ‘impossible’ rotaxanes whose axles lack any functional groups that would allow their direct synthesis by other means. Intriguingly, by varying the order of bond-forming steps, we can effectively choose which end of an axle the macrocycle is loaded onto, enabling the synthesis of both hands of a single target using the same reactions and building blocks.

Chiroptical Properties of Mechanically Interlocked Molecules

AbstractMechanically Interlocked Molecules (MIMs), such as catenanes, knots, and rotaxanes, are a class of molecules that possess mechanical bonds. These bonds constitute an entanglement in space between components of the MIMs that cannot be separated without breaking a participating covalent bond. Although it is possible to synthesize chiral MIMs with covalent stereogenic centers, this new bond opens up the possibilities of axial, planar and helical chirality, as well as topologically chiral compounds. A growing number of chiral MIMs have been investigated and employed in numerous applications, ranging from sensing to catalysis. While the investigation of the properties of MIMs is highly developed, it is also essential to study their chiroptical properties. In this review, we focus on the chiroptical properties of chiral MIMs. We discuss their electronic circular dichroism (ECD) since these properties have been analyzed in some detail in relation to their structures and stereochemistry. Although only a few examples have been described to date, we discuss the encouraging circularly polarized luminescence (CPL) properties of MIMs. The review also includes a recent study of vibrational circular dichroism (VCD) in mechanically planar chiral rotaxanes suggesting that this technique is a promising tool for analyzing the structures of MIMs. The study of the chiroptical properties of MIMs can have a large impact on their use in materials science or as catalysts. One of the key advantage of chiral MIMs is that they provide a means of generating efficient chiroptical switches that have a bright future in the context of multiple applications.

Enantioselective preparation of mechanically planar chiral rotaxanes by kinetic resolution strategy

Asymmetric synthesis of mechanically planar chiral rotaxanes and topologically chiral catenanes has been a long-standing challenge in organic synthesis. Recently, an excellent strategy was developed based on diastereomeric synthesis of rotaxanes and catenanes with mechanical chirality followed by removal of the chiral auxiliary. On the other hand, its enantioselective approach has been quite limited. Here, we report enantioselective preparation of mechanically planar chiral rotaxanes by kinetic resolution of the racemates via remote asymmetric acylation of a hydroxy group in the axis component, which provides an unreacted enantiomer in up to >99.9% ee in 29% yield (the theoretical maximum yield of kinetic resolution of racemate is 50%). While the rotaxane molecules are expected to have conformational complexity, our original catalysts enabled to discriminate the mechanical chirality of the rotaxanes efficiently with the selectivity factors in up to 16.

Single-Step Enantioselective Synthesis of Mechanically Planar Chiral [2]Rotaxanes Using a Chiral Leaving Group Strategy.

We report a one-step enantioselective synthesis of mechanically planar chiral [2]rotaxanes. Previous studies of such molecules have generally involved the separation of enantiomers from racemic mixtures or the preparation and separation of diastereomeric intermediates followed by post-assembly modification to remove other sources of chirality. Here, we demonstrate a simple asymmetric metal-free active template rotaxane synthesis using a primary amine, an activated ester with a chiral leaving group, and an achiral crown ether lacking rotational symmetry. Mechanically planar chiral rotaxanes are obtained directly in up to 50% enantiomeric excess. The rotaxanes were characterized by NMR spectroscopy, high-resolution mass spectrometry, chiral HPLC, single crystal X-ray diffraction, and circular dichroism. Either rotaxane enantiomer could be prepared selectively by incorporating pseudoenantiomeric cinchona alkaloids into the chiral leaving group.

Chiral rotaxanes go catalytic

Researchers in the UK have used a mechanically planar chiral rotaxane as the basis for an enantioselective gold catalyst (Chem 2020, DOI: 10.1016/j.chempr.2020.02.006). Stephen Goldup and Andrew He...

Synthesis of a Mechanically Planar Chiral Rotaxane Ligand for Enantioselective Catalysis

SummaryRotaxanes are interlocked molecules in which a molecular ring is trapped on a dumbbell-shaped axle because of its inability to escape over the bulky end groups, resulting in a so-called mechanical bond. Interlocked molecules have mainly been studied as components of molecular machines, but the crowded, flexible environment created by threading one molecule through another has also been explored in catalysis and sensing. However, so far, the applications of one of the most intriguing properties of interlocked molecules, their ability to display stereogenic units that do not rely on the stereochemistry of their covalent subunits, termed “mechanical chirality,” have yet to be properly explored, and prototypical demonstration of the applications of mechanically chiral rotaxanes remain scarce. Here, we describe a mechanically planar chiral rotaxane-based Au complex that mediates a cyclopropanation reaction with stereoselectivities that are comparable with the best conventional covalent catalyst reported for this reaction.

Vibrational circular dichroism spectroscopy for probing the expression of chirality in mechanically planar chiral rotaxanes.

Mechanically interlocked molecules can exhibit molecular chirality that arises due to the mechanical bond rather than covalent stereogenic units. Developing applications of such systems is made challenging by the absence of techniques for assigning the absolute configuration of products and methods to probe how the mechanical stereogenic unit influences the spatial arrangements of the functional groups in solution. Here we demonstrate for the first time that Vibrational Circular Dichroism (VCD) can be used to not only discriminate between mechanical stereoisomers but also provide detailed information on their (co)conformations. The latter is particularly important as these molecules are now under investigation in catalysis and sensing, both of which rely on the solution phase shape of the interlocked structure. Detailed analysis of the VCD spectra shows that, although many of the signals arise from coupled oscillators isolated in the covalent sub-components, intercomponent coupling between the macrocycle and axle gives rise to several VCD bands.

Stereoselective Synthesis of Mechanically Planar Chiral Rotaxanes

AbstractChiral interlocked molecules in which the mechanical bond provides the sole stereogenic unit are typically produced with no control over the mechanical stereochemistry. Here we report a stereoselective approach to mechanically planar chiral rotaxanes in up to 98:2 d.r. using a readily available α‐amino acid‐derived azide. Symmetrization of the covalent stereocenter yields a rotaxane in which the mechanical bond provides the only stereogenic element.

Stereoselective Synthesis of Mechanically Planar Chiral Rotaxanes.

Chiral interlocked molecules in which the mechanical bond provides the sole stereogenic unit are typically produced with no control over the mechanical stereochemistry. Here we report a stereoselective approach to mechanically planar chiral rotaxanes in up to 98:2 d.r. using a readily available α‐amino acid‐derived azide. Symmetrization of the covalent stereocenter yields a rotaxane in which the mechanical bond provides the only stereogenic element.

ChemInform Abstract: A Move in the Right Direction

AbstractReview: report on a synthetic strategy that allows the separation of enantiomerically ure planar chiral rotaxanes; 10 refs.

An efficient approach to mechanically planar chiral rotaxanes.

We describe the first method for production of mechanically planar chiral rotaxanes in excellent enantiopurity without the use of chiral separation techniques and, for the first time, unambiguously assign the absolute stereochemistry of the products. This proof-of-concept study, which employs a chiral pool sugar as the source of asymmetry and a high-yielding active template reaction for mechanical bond formation, finally opens the door to detailed investigation of these challenging targets.

Synthesis of a C1-symmetric Box macrocycle and studies towards active-template synthesis of mechanically planar chiral rotaxanes

A C1-symmetric Box macrocycle has been synthesized for the first time. The Box macrocycle along with other C1 and C2-symmetric Box ligands were evaluated and compared as ligands in the Cadiot–Chodkiewicz, oxidative Heck and CuAAC ‘click’ reactions as part of our studies towards achieving active-metal template synthesis of mechanically planar chiral rotaxanes. This study constitutes the first report of Cadiot–Chodkiewicz and CuAAC ‘click’ reactions using Box ligands, as well as the first dedicated study of oxidative Heck reactions using Box ligands.