When an amide group is distorted from its planar conformation, the conjugation between the nitrogen lone pair and the π* orbital of the carbonyl is disrupted and the reactivity towards nucleophiles ...is enhanced. Although there are several reports on the synthesis of activated twisted amides, amide activation through mechanical twisting is much less common. Here, we report twisted amides that are stabilized through their inclusion in a self-assembled coordination cage. When secondary aromatic amides are included in a T
-symmetric cage, the cis-twisted conformation is favoured over the trans-planar one-as evidenced by single-crystal X-ray diffraction analysis-revealing that the amide can twist by up to 34°. As a consequence of this distortion, the hydrolysis of amides is significantly accelerated upon inclusion.
Unusual demethylenation reactions of cyclopropanes under UV‐light irradiation were found within a cavity of a photoactive coordination cage. The reaction proceeded via a guest‐to‐host electron ...transfer owing to the highly electron‐deficient nature of the cage. The reactions were highly chemoselective and enabled late‐stage derivatization of a steroid molecule, which led to a totally new un‐natural steroid.
Cage power has enabled a unique reaction with the demethylenation of cyclopropanes initiated by guest‐to‐host electron transfer under irradiative conditions. The reaction proceeds with remarkable chemoselectivity and high yields.
Even flexible linear substrates are conformationally fixed within the hydrophobic confined cavities of enzymes. This enables preorganization of the substrates and their positioning in close proximity ...to the active center to facilitate stereo- and site-selective reactions. Here, we demonstrate the site-selective electrophilic addition of linear diterpenoids within a self-assembled coordination cage. The reactions proceed through folding of the linear substrates into a U-shaped conformation, which results in noncovalent protection of internal CC bonds to enhance the site selectivity.
One-Step Synthesis of [16]Helicene Mori, Kazuyuki; Murase, Takashi; Fujita, Makoto
Angewandte Chemie (International ed.),
June 1, 2015, Letnik:
54, Številka:
23
Journal Article
Recenzirano
A single‐strand arylene–vinylene precursor containing four phenylene and three naphthylene units linked together with six vinylene spacers undergoes helical folding via sextuple photocyclization to ...give a 16helicene core in a single step. The phenylene and naphthylene units are arranged in the precursor such that unfavorable side reactions (anthracene or benzoperylene formation) are avoided, and this is the key to the success of the one‐step synthesis of 16helicene, which is the longest nhelicene that has been synthesized to date.
An aromatic spiral layer: A 16helicene core was prepared in a single step by sextuple photocyclization from a single‐strand arylene–vinylene precursor containing four phenylene and three naphthylene units linked by six vinylene spacers. X‐ray crystallographic analysis revealed the triple‐layered structure. A new guideline for the design of precursor olefins resulted in the longest helicene synthesized to date.
This Review discusses, along with the historical background, the principles as well as proof‐of‐concept studies of the crystalline sponge (CS) method, a new single‐crystal X‐ray diffraction (SCXRD) ...method for the analysis of the structures of small molecules without sample crystallization. The method uses single‐crystalline porous coordination networks (crystalline sponges) that can absorb small guest molecules within their pores. The absorbed guest molecules are ordered in the pores through molecular recognition and become observable by conventional SCXRD analysis. The complex {(ZnI2)3(tpt)2⋅x(solvent)}n (tpt=tris(4‐pyridyl)‐1,3,5‐triazine) was first proposed as a crystalline sponge and has been most generally used. Crystalline sponges developed later are also discussed here. The principle of the CS method can be described as “post‐crystallization” of the absorbed guest, whose ordering is templated by the pre‐latticed cavities. The method has been widely applied to synthetic chemistry as well as natural product studies, for which proof‐of‐concept examples will be shown here.
Crystal growth is not needed for single‐crystal X‐ray structure analysis when the crystalline sponge method is used. This method makes use of single‐crystalline porous coordination networks (“crystalline sponges”) that can absorb small guest molecules within the pores and make the absorbed guests observable by conventional single‐crystal diffraction. This Review focuses on the principles of this approach as well as proof‐of‐concept studies.
With increasing ring-crossing number (c), knot theory predicts an exponential increase in the number of topologically different links of these interlocking structures, even for structures with the ...same ring number (n) and c. Here, we report the selective construction of two topologies of 12-crossing peptide 4catenanes (n = 4, c = 12) from metal ions and pyridine-appended tripeptide ligands. Two of the 100 possible topologies for this structure are selectively created from related ligands in which only the tripeptide sequence is changed: one catenane has a T
-tetrahedral link and the other a three-crossed tetrahedral link. Crystallographic studies illustrate that a conformational difference in only one of the three peptide residues in the ligand causes the change in the structure of the final tetrahedral link. Our results thus reveal that peptide-based folding and assembly can be used for the facile bottom-up construction of 3D molecular objects containing polyhedral links.
"The story is told by THE inventor-pioneer-master in the field and is accompanied by amazing illustrations... it will become an absolute reference and a best seller in chemistry!" Alberto Credi "... ...the great opus on the mechanical bond. A most impressive undertaking!" Jean-Marie Lehn Congratulations to co-author J. Fraser Stoddart, a 2016 Nobel Laureate in Chemistry.
In molecules, the mechanical bond is not shared between atoms-it is a bond that arises when molecular entities become entangled in space. Just as supermolecules are held together by supramolecular interactions, mechanomolecules, such as catenanes and rotaxanes, are maintained by mechanical bonds. This emergent bond endows mechanomolecules with a whole suite of novel properties relating to both form and function. They hold unlimited promise for countless applications, ranging from their presence in molecular devices and electronics to their involvement in remarkably advanced functional materials. The Nature of the Mechanical Bond is a comprehensive review of much of the contemporary literature on the mechanical bond, accessible to newcomers and veterans alike. Topics covered include: Supramolecular, covalent, and statistical approaches to the formation of entanglements that underpin mechanical bonds in molecules and macromolecules Kinetically and thermodynamically controlled strategies for synthesizing mechanomolecules Chemical topology, molecular architectures, polymers, crystals, and materials with mechanical bonds The stereochemistry of the mechanical bond (mechanostereochemistry), including the novel types of dynamic and static isomerism and chirality that emerge in mechanomolecules Artificial molecular switches and machines based on the large-amplitude translational and rotational motions expressed by suitably designed catenanes and rotaxanes. This contemporary and highly interdisciplinary field is summarized in a visually appealing, image-driven format, with more than 800 illustrations covering both fundamental and applied research. The Nature of the Mechanical Bond is a must-read for everyone, from students to experienced researchers, with an interest in chemistry's latest and most non-canonical bond. Read the Preface
A 2‐biphenylacetylene was fixed into a specific conformation within the confined cavity of a hollow cage, where it underwent a regioselective spirocyclization in the presence of an electrophile. A ...5‐endo‐dig cyclization proceeded selectively in the cage, which stands in sharp contrast to the 6‐endo‐dig cyclization that normally occurs in common organic media. The folded conformation adopted by the substrate within the cage was examined by 1H NMR spectroscopy and X‐ray crystallographic analysis.
A regioselective spirocyclization of a 2‐biphenyl acetylene was achieved by virtue of a spatial constraint in a self‐assembled molecular cage. The unusual, folded conformation in the cavity alters the selectivity of the electrophilic cyclization from 6‐endo‐dig to 5‐endo‐dig to form a hindered spiro compound. NBS= N‐bromosuccinimide; NIS= N‐iodosuccinimide.
Cavity creation is a key to the origin of biological functions. Small cavities such as enzyme pockets are created simply through liner peptide folding. Nature can create much larger cavities by ...threading and entangling large peptide rings, as learned from gigantic virus capsids, where not only chemical structures but the topology of threaded rings must be controlled. Although interlocked molecules are a topic of current interest, they have for decades been explored merely as elements of molecular machines, or as a synthetic challenge. No research has specifically targeted them for, and succesfully achieved, cavity creation. Here we report the emergence of a huge capsular framework via multiple threading of metal-peptide rings. Six equivalent C
-propeller-shaped rings, each consisting of four oligopeptides and Ag
, are threaded by each other a total of twelve times (crossing number: 24) to assemble into a well-defined 4 nm-sized sphere, which acts as a huge molecular capsule.
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