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The alkylation of some secondary amide functions with a dimethoxybenzyl (DMB) group in oligomers of 8‐amino‐2‐quinolinecarboxylic acid destabilizes the otherwise favored helical conformations, and allows for cyclization to take place. A cyclic hexamer and a cyclic heptamer were produced in this manner. After DMB removal, X‐ray crystallography and NMR show that the macrocycles adopt strained conformations that would be improbable in noncyclic species. The high helix folding propensity of the main chain is partly expressed in these conformations, but it remains frustrated by macrocyclization. Despite being homomeric, the macrocycles possess inequivalent monomer units. Experimental and computational studies highlight specific fluxional pathways within these structures. Extensive simulated annealing molecular dynamics allow for the prediction of the conformations for larger macrocycles with up to sixteen monomers., Frustrating folding propensity by imposing a macrocyclic structure to an otherwise helical backbone produces improbable yet stable strained molecular shapes. Both experiments and computational studies show how aromatic oligoamide foldamers constrained within a macrocycle try to fulfill their strong propensity to adopt helical conformations by forming local loops and unfolded sites that connect helical segments. Defined fluxional conformational pathways can be evidenced in such molecules.

This work reports that cyclophanes and their [2]catenanes were synthesized by the SN Ar reactions of disubstituted adamantanes bearing halophenol units and 3,6-dichlorotetrazine in moderate yields. In the crystalline state, the cyclophanes had hexagonal structures with a cavity. The [2]catenanes were composed of two macrocycles that were singly interlocked and orthogonally arranged, indicating the construction from eight component molecules through eight C-O bonds in a one-step reaction in up to 33 % yield. The cyclophanes were assembled to afford a supramolecular organic framework in the solid state, which exhibited permanent intrinsic porosity and adsorption of leaf alcohol or aldehyde in a single-crystal to single-crystal fashion. The molecular structures of the liquid guests were determined by single-crystal X-ray analysis. The formation of catenanes and the use of cyclophane-based porous crystals in the crystalline sponge method may be largely ascribed to the solvophobic effects and the van der Waals interactions that originate in the aliphatic and bulky nature of the adamantane units.

Disubstituted adamantanes having pyrogallol derivatives as V-shaped host molecules were synthesized to prepare complexes with carboranes, which are representative spherical guest molecules for macrocyclic compounds, including calixarenes and cyclotriveratrylenes. The crystallization of o-carborane (a) and 1,3-bis(3,4,5-trimethoxyphenyl)adamantane (1) in toluene resulted in the formation of inclusion crystals (1a) in a 1 : 1 ratio. X-ray crystallographic analysis revealed that two oxygen atoms in 1 interact with two hydrogen atoms of a through CH⋯O interactions to afford the complexes. In the case of 1,3-bis(3,4,5-triethoxyphenyl)adamantane (2), no inclusion crystal was obtained due to steric hindrance of the ethyl groups. Furthermore, the crystallization of 1 and a benzoquinone derivative (b) provided reddish crystals (1b) with a 1 : 2 host : guest complexation stoichiometry, where lone pair⋯π interactions in the complexes were observed in addition to donor–acceptor interactions.

In previous research studies, various types of prismatic cage-shaped molecular containers have been prepared and evaluated in terms of their guest inclusion properties. Basically, most of these molecular cages have a cationic or electron-deficient nature, and exhibit strong affinity mainly toward electron-rich aromatic guests. On the other hand, there is no report concerning anionic prismatic cages that are expected to recognize cationic polyaromatic guests with various structures and functions. In this manuscript, we present the preparation of hexakis(spiroborate)-type molecular cages, which was achieved by the reaction of phenylene- or biphenylenebis(dihydroxynaphthalene), hexahydroxytriphenylene, and boric acid in N,N-dimethylformamide. Their triangular prismatic hollow structures were confirmed by X-ray crystallographic analysis, and it was found that both phenylene- and biphenylene-bridged spiroborate cages have internal cavities of the corresponding size. It was also revealed that tetra(n-butylammonium) cations located inside the cavity and between the two adjacent spiroborate cages resulted in the formation of a one-dimensional columnar array. The molecular recognition behavior of the spiroborate cages was evaluated using tris(pyridinium)triazines as tricationic aromatic guests. 1H NMR measurement implied that a discrete 1 : 1 host–guest complex was formed when 1 equiv. of guest was added to the cage, whereas infinite one-dimensional aromatic stacks were constructed by the addition of 2 equiv. of guest.

N-Phenylbenzenesulfonamides exist preferentially in (+)- or (−)-synclinal conformations, which place the aromatic rings at both ends in the same direction with a twist. We have systematically analyzed the crystal structure of secondary aromatic sulfonamides bearing methyl, ethyl, and/or methoxy groups on the benzene rings. Intermolecular hydrogen bonding between the sulfonamide protons and sulfonyl oxygens was observed in 81 out of 85 crystals. The intermolecular hydrogen-bonding patterns could be classified into four types, i.e. Dimeric, Zigzag, Helical, and Straight patterns, with retention of the synclinal conformation of the sulfonamide moiety. We investigated the relationship between the hydrogen-bonding pattern and the proportion of the compounds that show chiral crystallization. On the basis of our classification of the intermolecular hydrogen bonds of aromatic sulfonamides, the crystals with Dimeric and Zigzag patterns, which both have enantiomeric synclinal conformers, intrinsically become achira...

An adamantane-based macrocycle possessing eight hydroxyl groups (1) was synthesized, in which the macrocyclic framework comprises two disubstituted adamantane molecules bearing phenyl derivatives connected to two biphenylene spacers by oxygen atoms. Furthermore, functionalized macrocycles containing methyl (2) and methoxycarbonylmethyl (3) groups were prepared. From the X-ray crystallographic analysis, the backbone of the macrocycles in all crystals had a nearly hexagonal shape with a cavity and these macrocycles could be arranged into different tubular structures dependent on the substituents. In acetone, macrocycle (1) formed stable hollow spherical aggregates with multilayer membranes. In contrast, macrocycle (3) exhibited no production of self-assembled materials in chloroform. The addition of hexane into the solution caused the generation of solid spheres and their fused network aggregates, which were finally transformed into crystals owing to the solvent effects.

A simple method for the synthesis of monoselenides and diselenides having 1,2,3-triazole ring is described herein. The three component reaction of ethynylstibanes, organic azides, and selenium powder is catalyzed by CuI (10 mol%) using 1,10-phenanthroline as the ligand (10 mol%) under aerobic conditions. Either selenides or diselenides can be synthesized by selecting the appropriate amount of selenium powder for otherwise identical reaction conditions. The obtained selenides and diselenides having a 1,2,3-triazole ring are all novel compounds. By using an antimony reagent, this one-pot reaction provides regioselective double Se-arylation under simple reaction conditions.

Two novel 20-hydroxyvitamin D3 analogues (4a,b) with the A-ring modification have been synthesized by a convergent manner. An alternative pathway of vitamin D3 metabolism by cytochrome P450scc CYP11A1 was reported to afford 20-hydroxyvitamin D3 (3), functions of which remain to be explored. Based on the structure of the 20-hydroxy metabolite, novel analogues (4a,b) with the modifications, including the 1α-hydroxy, 25-hydroxy and 2α-methyl groups, have been designed. The side chain of the requisite CD-ring portions (9a,b) was introduced by Grignard reaction as a key step, and the stereochemistry at the C20 position was confirmed by the X-ray crystal structure analysis of the synthetic intermediate (8b). Preliminary biological characterization using the bovine thymus vitamin D receptor suggested that the introduction of the active motifs into the 20-hydroxyvitamin D3 scaffold elevated the receptor affinity.

Phosphole-fused π-conjugated acenes have been attracting interest because of the attractive features of the phosphole moiety, such as fluorescence and chemically modifiable properties. Herein, 6-phenyl-6H-benzo[f]naphtho[2,3-b]phosphoindole was prepared by reacting dichlorophenylphosphine with a dilithium intermediate derived from 3,3′-dibromo-2,2′-binaphthyl. Various derivatives, such as a phospholium salt and a borane–phosphole complex with functional groups on the phosphorus atom were synthesized using the obtained phosphole as a common starting material. Single-crystal X-ray analysis of the parent benzo[f]naphtho[2,3-b]phosphoindole revealed that the pentacyclic ring is almost planar. Fluorescence spectroscopy data showed that the phosphole derivatives, such as phosphine oxide and the phospholium salt and borane complex exhibited photoluminescence in chloroform.

The expectation that antimony (Sb) compounds should display phosphorescence emissions based on the “heavy element effect” prompted our interest in the introduction of antimony to a biaryl as the bridging atom in a fused heterole system. Herein, the synthesis, molecular structures, and optical properties of novel benzene-fused heteroacenes containing antimony or arsenic atoms are described. The stiboles and arsole were prepared by the condensation of dibromo(phenyl)stibane or dichloro(phenyl)arsine with dilithium intermediates derived from the corresponding dibromo compounds. Nuclear magnetic resonance (NMR) spectroscopy and X-ray crystal analysis revealed that the linear pentacyclic stibole was highly symmetric in both the solution and crystal states. In contrast, the curved pentacyclic stibole adopted a helical structure in solution, and surprisingly, only M helical molecules were crystallized from the racemate. All synthesized compounds produced very weak or no emissions at room temperature or in the solid state. In contrast, the linear penta- and tetracyclic stiboles exhibited clear phosphorescence emissions in the CHCl3 frozen matrix at 77 K under aerobic conditions.

Four disubstituted adamantane-based molecules containing N-heterocyclic moieties were designed and synthesized as hydrogen bond acceptors for the preparation of co-crystals with hydrogen bond donors. Co-crystal screening of the four adamantane-based molecules with terephthalic acid was firstly attempted in mixed solvents. Only the compound with methylimidazole moieties (1) afforded the co-crystals in 1:1 ratio, whereas the others gave individual crystals. X-ray crystallographic analysis demonstrated that the hydrogen bonds between the imidazole and the carboxylic acid moieties of both components provided infinite one-dimensional chains that were assembled into network structures through CH···O interactions. When isophthalic acid or resorcinol was employed as the partner, the co-crystals were similarly generated by intermolecular non-covalent interactions. The selective co-crystal formation of 1 is mainly attributed to the increase of strength of the hydrogen-bonding acceptor on the nitrogen atoms of the N-heterocyclic moieties and the stabilization of the hydrogen-bonded complexes due to the electron-donating ability and the steric effect of the methyl groups.

The enantiopure macrocyclic tetraimines containing adamantane moieties (1, 2) were synthesized from (R,R)- or (S,S)-1,2-cyclohexanediamine and a disubstituted adamantane derivative having salicylal...

To explore the utility of bis(dihydroxynaphthalene) ligands for the construction of supramolecular structures, we demonstrated the preparation of cage-shaped complexes by combining these ligands with hexacoordinate titanium(IV). The reaction of biphenylenebis(dihydroxynaphthalene) with TiO(acac)2 proceeded in the presence of N-methylmorpholine in DMF and an M2L3-type cage was obtained by self-organization. As an extension of this work, the preparation of heterobimetallic molecular cages was examined by using combinations of titanium(IV), palladium(II) or platinum(II), and pyridyldihydroxynaphthalenes. Ti(IV)/Pd(II) cages were prepared in one pot by treatment of the pyridyldihydroxynaphthalene ligands with TiO(acac)2 followed by PdCl2(MeCN)2. In the preparation of Ti(IV)/Pt(II) cages, platinum(II)-bridged bis(dihydroxynaphthalene) ligands were isolated in advance from the reaction of pyridyldihydroxynaphthalene ligand precursors with K2PtCl4, which were then deprotected and reacted with TiO(acac)2 in the same conditions as those for biphenylenebis(dihydroxynaphthalene). The precise structures of the Ti(IV)/Pd(II) and Ti(IV)/Pt(II) heterobimetallic cages were fully elucidated by X-ray crystallographic analysis.

Although cis-trans lactam amide rotation is fundamentally important, it has been little studied, except for a report on peptide-based lactams. Here, we find a consistent relationship between the lactam amide cis/trans ratios and the rotation rates between the trans and cis lactam amides upon the lactam chain length of the stapling side-chain of two 7-azabicyclo[2.2.1]heptane bicyclic units, linked through a non-planar amide bond. That is, as the chain length increased, the rotational rate of trans to cis lactam amide was decreased, and consequently the trans ratio was increased. This chain length-dependency of the lactam amide isomerization and our simulation studies support the idea that the present lactam amides can spin through 360 degrees as in open-chain amides, due to the occurrence of nitrogen pyramidalization. The tilting direction of the pyramidal amide nitrogen atom of the bicyclic systems is synchronized with the direction of the semicircle-rotation of the amide., Cis-trans lactam amide rotation is a fundamental process and its understanding might aid molecular design. Here, the authors report the synthesis and study of bicyclic lactams which undergo spin through 360 degrees as in open-chain amides, due to the occurrence of nitrogen pyramidalization.

A disubstituted adamantane derivative bearing chloropyrimidine units (1) was synthesized as an acyclic host molecule to construct guest-inclusion crystalline materials, and the molecular structures of these crystalline materials were determined by X-ray crystallographic analysis. The crystallization of 1 and trans-decahydronaphthalene (a) in chloroform afforded co-crystal (1a) with 2 : 1 host : guest complexation stoichiometry. The guest molecule was accommodated within the cavity of the cyclic dimers of 1 built from Cl⋯π interactions between the chloropyrimidine units. These complexes were assembled into network structures through intermolecular interactions. From the Hirshfeld surface analysis and the 2D fingerprint plot of a in co-crystal 1a, the maximum contribution is from the H⋯H contacts between 1 and a, indicating that the main driving force for the guest inclusion is dispersive force. Co-crystals containing cycloalkanes and cycloalkenes (b–f) and having the same stoichiometry were obtained under identical conditions. In all the co-crystals, the shapes and sizes of the cyclic dimers and the molecular networks were similar to those of crystal 1a, and the molecular structures of the guests were characterized.

Hydrogen-bonding compound (1), which is composed of p-terphenyl and adamantanecarboxylic acid, acted as a host molecule for three amides, respectively, forming crystals. Crystals containing the amides (1a and 1b) were produced from N,N-dimethylformamide (DMF) and N,N-diethylformamide (DEF) in 1:2 host:guest complexation stoichiometry, respectively, whereas guest-free crystals (1c) were generated from N-methylformamide (NMF). In the crystal structures of 1a and 1b, carboxylic acids of 1 interact with oxygen atoms of the amide guests through hydrogen bonds to afford network and layer architectures. Crystals 1a and 1b were given from equimolar binary mixtures of DMF or DEF and NMF, respectively. Further, from a mixture of DMF and DEF, guest-inclusion crystals 1d different from 1a and 1b were formed, where DMF was preferentially accommodated. Competition experiments revealed that the selectivity order of 1 for the amide guests was DMF > DEF ≫ NMF.

Adamantane-based bis- and tris-catechols were synthesized to examine the effect of hydrogen bonds on the arrangement and packing of the components in the crystalline state. Single-crystal X-ray crystallographic analysis revealed that hydrogen bonds formed by the hydroxyl groups of catechol groups play essential roles in the production of various types of unique structures. 1,3-Bis(3,4-dihydroxyphenyl)adamantane (1) provided hydrogen-bonded network structures composed of helical chains in crystal from chloroform/methanol, and layer structures in crystal from ethyl acetate/hexane. The complexation of 1 with 1,3,5-trinitrobenzene or 1,2,4,5-tetracyanobenzene resulted in the formation of co-crystals, respectively. One-dimensional hydrogen-bonded structures were constructed from the adamantane-based molecules, which participated in charge-transfer interactions with guests. 1,3,5-Tris(3,4-dihydroxyphenyl)adamantane also afforded crystal, and the components were assembled into infinite polymers.

Ring-closing metathesis (RCM) of ynamides, having alkene substituents of various lengths on the side chain, was demonstrated using the second-generation Grubbs catalyst. When the reaction of ene-ynamides was carried out in the presence of 5 mol% of the catalyst, RCM proceeded smoothly to give quinoline or isoquinoline derivatives having a dienamide unit in good yields. Furthermore, RCM of ene-ynamides, having one more carbon on the side chain, proceeded smoothly to provide seven-membered heterocycles having a dienamide component. Similarly, eight-membered heterocycles, diazocine and benzodiazocine, were also synthesized by RCM of ene-ynamides in good yields.

1,1-Disubstituted indazolium hexafluorophosphates were synthesized via intramolecular electrophilic amination reactions under mild conditions. The crystal structures were determined and are consistent with the presence of a stable N-N bond, which can be cleaved by hydrogenation. Both experimental and computational studies suggest a covalent bonding character of the N-N bond, with diminished aromaticity of the newly formed pyrazolium ring due to the quaternary ammonium atom (N1), in contrast to the aromatic character of the parent indazole.

The separation of p-xylene from a mixture of four C8 alkylaromatics has been realized through a highly selective inclusion by an acyclic host molecule (1) via crystallization. In the crystal structure, the guest molecule was included in the cavity of the cyclic dimer of 1. Further, the host molecule specifically discriminated p-xylene from a mixture of eight C8 and C9 aromatic compounds.

A naphthalenediimide-based macrocycle with adamantane parts was synthesized from naphthalenetetracarboxylic dianhydride and 1,3-adamantanedimethanamine. The addition of methanol to a chloroform solution of the macrocycle led to formation of spherical species and their fused network aggregates, which were transformed into crystals. X-ray analysis showed a crescent-shaped molecular structure. In the presence of perylene, charge-transfer co-crystals of sandwich-type complexes were generated via self-assembly of nanostructures.

The aim of this study is to evaluate the relative stability of pharmaceutical cocrystals consisting of paracetamol (APAP) and oxalic acid (OXA) or maleic acid (MLA).These observations of cocrystal stability under various conditions are useful coformer criteria when cocrystals are selected as the active pharmaceutical ingredient in drug development.The relative stability was determined from the preferentially formed cocrystals under various conditions.Cocrystal of APAP-OXA was more stable than that of APAP-MLA in a ternary cogrinding system and possessed thermodynamical stability. On the other hand, when grinding with moisture or maintaining at high temperatures and relative humidity conditions, APAP-MLA was more stable, and OXA converted to OXA dihydrate. In the slurry method, APAP-OXA was more stable in aprotic solvents because the APAP-OXA with low-solubility product precipitated.The relative stability order was affected by preparing conditions of presence of moisture. This order might attribute to the small difference of crystal structure in the extension of the hydrogen bond network.

Twin-bowl-shaped tris-(spiroborate) cyclophanes bearing pyridyl groups have been prepared for the construction of proton-responsive supramolecular polymers. Preparation of the pyridyl twin bowls was carried out by the reaction of 6,6′-(3-pyridyl)-2,2′,3,3′-tetrahydroxy-1,1′-binaphthyls and an equimolar amount of boric acid in N,N-dimethylformamide in self-organization manner, as previously reported. The reversible acid/base response of the pyridyl twin bowls was evaluated by the addition of hydrochloric acid and aqueous sodium hydroxide. The assembly disassembly modulation of the supramolecular polymers composed of pyridyl twin bowls and the tricationic iridium-(III) complex was also examined. Dissociation of the supramolecular polymers occurred by the addition of hydrochloric acid, and its reconstruction was realized by the addition of aqueous sodium hydroxide. The opposite behavior was observed when the dianionic palladium-(II) complex was employed as a guest. The addition of acid led to the formation o...

The Cu-catalyzed azide-alkyne cycloaddition by the reaction of various ethynylstibanes with benzylazide in the presence of CuBr (5 mol%) under aerobic conditions led to the formation of trisubstituted 5-organostibano-1H-1,2,3-triazoles. Further, the acyl-induced deantimonation of 5-stibanotriazoles with acyl chlorides in the presence of N,N-dimethyl-4-aminopyridine and triethylamine afforded the corresponding trisubstituted 5-acyltriazoles in moderate-to-good yields.

Trisubstituted 5-stibano-1H-1,2,3-triazoles 3 was synthesized by the Cu-catalyzed [3 + 2] cycloaddition of ethynylstibane 1 with benzyl azide 2 in the presence of CuBr (5 mol%) under aerobic conditions. 5-Stibanotriazole 3 was treated with an equimolecular amount of phenyllithium (PhLi) in anhydrous THF under argon atmosphere at −78 °C. Subsequent treatment with various electrophiles formed 1,4,5-trisubstituted-1,2,3-triazoles 5 containing a benzyl moiety. This reaction is a novel example of an antimony (Sb) – lithium (Li) exchange reaction for the functionalization of heterocycles.

Three tetrapodal tetraaryladamantanes bearing imidazole derivatives exhibit unique self-assembly and crystallization behaviors, including hollow spherical aggregation, a morphological change by fus...

Our NMR, IR/Raman, CD spectroscopic, and X-ray crystallographic studies, as well as accelerated molecular dynamics simulations, showed that alternating hybrid α/β-peptides containing a bicyclic β-proline surrogate form unique extended curved folds, regardless of the peptide length and solvent environment. It is suggested that extended β/PPII structures are preferred in the insulating α-alanine moieties between the rigid bicyclic β-proline structures. These hybrid peptides inhibit p53-MDM2 and p53-MDMX protein-protein interactions.

Neighboring group participation is defined as the action of a substituent to stabilize a transition state or an intermediate by forming a bond or a partial bond with the reaction center. In addition to the primary interaction with the nearest neighboring group, secondary interactions involving another neighboring group(s) could also occur in principle. Here, we revisit this issue by examining the influence of secondary interactions on the stability and reactivity of the putative iminylium cation intermediates, formed by N-O bond cleavage of 1-tetralone oxime systems. A direct observation of a peri-bromo-iminylium intermediate in solution supported the involvement of iminylium cations and the stabilizing effect of secondary interactions arising from a distal tandem substituent. Both experimental and computational findings support the idea that secondary interactions of a tandem-neighboring group on the primary peri-heteroatom (Br, Cl, and O(Me))-iminylium bonding interaction, i.e., a weak halogen bonding interaction (ester (nitro) oxygen-halogen bonding) and an unprecedented hydrogen bonding interaction between a nitro oxygen atom and a CH3O hydrogen atom, are crucial determinants of the reaction pathway, leading to either overwhelmingly selective syn-migration of the oxime functionality or covalent bond formation under acid-catalyzed Beckmann rearrangement conditions.

Adamantane-based molecules possessing two or three pyrogallol derivatives as acyclic host molecules were developed to examine their potential to form complexes with pyridinium-based dicationic compounds, which are well known as guest molecules of macrocycles, including calixarenes, pillararenes, and others. The complexation of paraquat (3) with 1,3-bis(3,4,5-trimethoxyphenyl)adamantane (1) in acetone afforded reddish brown cocrystals with a 2 : 1 host : guest complexation stoichiometry. X-ray crystallographic analyses revealed that one guest molecule is included in the space between two adamantane-based molecules possessing bent and rigid frameworks, where donor–acceptor and CH⋯π interactions between 32+ and the trimethoxyphenyl groups in 1 were observed. Further, the mixing of 3 and 1,3,5-tris(3,4,5-trimethoxyphenyl)adamantane (2) gave cocrystals with a 1 : 2 stoichiometry, where one dicationic guest is surrounded by four electron-rich trimethoxyphenyl groups of two molecules of 2, resulting in the formation of charge-transfer complexes through similar non-covalent interactions.

Europium(III)–phosphine oxide porous coordination polymers (Eu–PCPs) constructed from Eu(OTf)3 and tris(4-(4′-carboxylphenyl)phenyl)phosphine oxide as ligands are reported. X-Ray diffraction data of Eu–PCPs are collected at 273 K with synchrotron radiation. The europium complex is shown to crystallize in the centrosymmetric orthorhombic space group Pcca. The Eu atom is surrounded by eight neighboring oxygen atoms from six ligands and a coordinated DMF molecule. Furthermore, the two Eu centers are quadruply bridged by four carboxylates. They exhibit an infinite three-dimensional structure that incorporates an open pore structure, which is thermally robust and has an N2 Brunauer–Emmett–Teller surface area of 58.5 m2 g−1 and a micropore volume of 0.756 cm3 g−1. Excitation of the materials led to five sharp emission peaks arising from the 5D0 → 7FJ transitions (J = 0, 1, 2, 3 and 4). The absolute quantum yield of Eu–PCPs is determined as 22% at room temperature. In addition, exposure of single crystals of Eu–PCPs to H2O vapor causes attenuation of the luminescence intensity. This process involves a single-crystal-to-single-crystal transformation. In the crystal structures of the Eu–PCPs, the ligand exchange from DMF to H2O, which acts to quench the lanthanide luminescence, is directly observed.

Microtropins Q-W, (2S,3R)-2-ethyl-2,3-dihydroxybutyrate of various glucosides and glucose, as well as three ent-labdane diterpenoid glucosides, named microtropiosides G, H and I, an ursane-type triterpene diglucoside and a flavonoid glycoside were isolated from the MeOH extract of the leaves of Microtropis japonica. The structure of microtropioside A, also isolated from the branches of M. japonica, was elucidated spectroscopically in a previous experiment and was found to possess a rare seven-membered oxyrane ring. Its structure was confirmed by X-ray crystallographic analysis of its pentaacetate.

Cu-catalyzed tandem cyclization of 2-(2-iodophenyl)imidazo[1,2-a]pyridines with selenium for the practical synthesis of the benzo[b]selenophene-fused imidazo[1,2-a]pyridines occurred smoothly via Ullmann-type Se-arylation and Csp2–H selenation. A variety of benzo[b]selenophene-fused imidazo[1,2-a]pyridines were easily obtained in moderate-to-high yields. Single-crystal X-ray analysis of 2a revealed that the benzo[b]selenophene and imidazopyridine rings are almost coplanar. The maximum absorption of tetracyclic compound 2a was red-shifted by 45–47 nm from those of imidazo[1,2-a]pyridine and benzo[b]selenophene.

Cross-coupling is a fundamental reaction in the synthesis of functional molecules, and has been widely applied, for example, to phenols, anilines, alcohols, amines and their derivatives. Here we report the Ni-catalysed Stille cross-coupling reaction of quaternary ammonium salts via C–N bond cleavage. Aryl/alkyl-trimethylammonium salts [Ar/R–NMe3]+ react smoothly with arylstannanes in 1:1 molar ratio in the presence of a catalytic amount of commercially available Ni(cod)2 and imidazole ligand together with 3.0 equivalents of CsF, affording the corresponding biaryl with broad functional group compatibility. The reaction pathway, including C–N bond cleavage step, is proposed based on the experimental and computational findings, as well as isolation and single-crystal X-ray diffraction analysis of Ni-containing intermediates. This reaction should be widely applicable for transformation of amines/quaternary ammonium salts into multi-aromatics., The Stille reaction is a long-standing method for the construction of carbon-carbon bonds by coupling aryl halides with organotin compounds. Here the authors report a Stille coupling between aryl ammonium salts and arylstannanes catalysed by nickel.

Three-dimensional arrays of dipolar rotors were constructed as single crystals of molecular gyrotops, which are macrocage molecules with a bridged dipolar rotor. In this study, we synthesized novel molecular gyrotops with a five-membered heteroring, i.e., furan-diyl (1), thiophene-diyl (2), and selenophene-diyl (3), and investigated the temperature-dependent orientation and rotation of the dipolar rotors inside the crystal. Unfortunately, furan derivative 1 did not crystallize; however, crystal structures of the other molecular gyrotops, i.e., 2 and 3, showed three-dimensional arrays of dipolar rotors. Thermal order–disorder transitions of the dipolar rotor orientation inside the crystal were observed in 2 and 3 with the transition temperature in selenophene derivative 3 being lower than that of thiophene derivative 2. This may be ascribed to subtle differences in the molecular structure, e.g., the intersection angle between two Si–C(aryl) bonds corresponding to the rotation axis. In accordance with the t...

Trisubstituted 5-stibano-1H-1,2,3-triazoles were synthesized in moderate to excellent yields by the Cu-catalyzed [3 + 2] cycloaddition of a ethynylstibane with organic azides in the presence of CuBr (5 mol %) under aerobic conditions. The reaction of 5-stibanotriazole with HCl, I2, and NOBF4 afforded 1-benzyl-4-phenyltriazole, 1-benzyl-5-iodo-4-phenyltriazole, and a pentavalent organoantimony compound, respectively.

Novel organoantimony and bismuth compounds, 2-(di-p-tolylstibano)- and 2-(di-p-tolylbismuthano)-N-p-tolylbenzamide (2 and 3), bearing an amide moiety as the pendant arm were synthesized and characterized by NMR, IR, single-crystal X-ray diffraction, and elemental analyses. The molecular structures of compounds 2 and 3 showed the presence of intramolecular interactions between the antimony/bismuth and carbonyl oxygen atoms in the solid state, respectively. The central atoms (Sb and Bi) exhibited a pseudo trigonal bipyramidal structure. Compounds 2 and 3 showed potent antiproliferative activity in all the tested cell lines. In particular, compound 3 containing bismuth was more sensitive than compound 2 containing antimony.

A disubstituted adamantane derivative having chloropyrimidine units (1) was utilized as a V-shaped host molecule to create inclusion crystals and to elucidate the molecular structures of the guests by X-ray crystallographic analysis. The crystallization of 1 and 1,3,5,7-cyclooctatetraene (a) in chloroform resulted in the formation of co-crystal (1a) with 2:3 host:guest complexation stoichiometry. Host 1 was assembled into a molecular network composed of double layer structures bearing channels where guest molecules (a) were accommodated. Co-crystals (1b, 1c) containing 1,3-cyclooctadiene (b) and 1,5-cyclooctadiene (c) were obtained at identical stoichiometry under similar conditions. The host molecules arrangement in both 1b and 1c was similar to that of 1a. In each case, guest molecules b and c were accommodated in the channels formed between the layers of the host molecules. In all co-crystals, the molecular structures of the guests a‒c, along with the host frameworks, were determined by crystallographic analysis.

From the stems of Croton cascarilloides, further crotofolane-type diterpenoids, named crotocascarins L-Q (1-6), and a rearranged one (7), named neocrotocascarin were isolated. Their structures were elucidated from spectroscopic evidence. Also, the structures of crotocascarin O (4) and neocrotocascarin (7) were determined by X-ray crystallographic analyses. As a result, neocrotocascarin (7) was found to possess a new carbon framework. A plausible mechanism for the formation of neocrotocascarin (7) is also discussed.

From the leaves of Meliosma lepidota ssp. squamulata, megastigmane glucosides with spiro-structures and megastigmanes were isolated. Their structures were determined by X-ray crystallographic analyses and spectroscopic investigation. The absolute structures of the megastigmanes were determined by the modified Mosher's method.

From the 1-BuOH-soluble fraction of a methanol (MeOH) extract of the leaves of Croton cascarilloides, crotofolanes: crotocascarins I-K, nor-crotofolane: crotocascarin γ, isocrotofolane glucoside and phenolic glycoside were isolated by a combination of various separation techniques. Their structures were elucidated mainly from the NMR spectroscopic evidence. The structure of crotocascarin K was first elucidated by spectroscopic analysis and then was confirmed by X-ray crystallographic analysis. Its absolute structure was finally determined by the modified Mosher's method. Isocrotofolane glucoside was found to possess a new skeleton, however, its absolute structure remains to be determined.

Lanthanide(III)-containing metallosupramolecular arrays were prepared in the crystalline state simply by mixing trifluoromethanesulfonate salts of yttrium(III), lanthanum(III), europium(III), terbium(III), erbium(III), and ytterbium(III) with a rac-tris(spiroborate) twin bowl in N,N-dimethylformamide (DMF). In the crystal, the lanthanide(III) ion coordinated to eight or nine DMF molecules to form spherical tricationic complexes, and the spiroborate twin bowl iteratively glued the complexes to each other to form one-dimensional arrays that were unidirectionally packed in the crystal. In each case, the array structure was stabilized by many aromatic C–H···π interactions and C–H···O hydrogen bonds between the twin bowls and the lanthanide(III) complexes. Among the lanthanide(III) ions, yttrium(III), terbium(III), erbium(III), and ytterbium(III) gave almost the same crystal lattice and packing, whereas a different array structure and crystal packing was observed when lanthanum(III) and europium(III) were used...

Because homooligomers of 7-azabicyclo[2.2.1]heptane-2-endo-carboxylic acid, a bridged β-proline analogue with a substituent installed at the remote C4-bridgehead position, completely biased the amide cis-trans equilibrium to the cis-amide structure, we expected that introduction of a substituent at the C1-bridgehead position adjacent to the carboxylic acid moiety, rather than the remote C4-bridgehead position, would tip the cis-trans amide equilibrium toward trans-amide structure without the aid of hydrogen bonding. Thus, in this work we established an efficient synthetic route to an optically active bicyclic analogue of 1,1-disubstituted β-proline, bearing a substituent at the C1-bridgehead position. Crystallographic, spectroscopic, and computational studies showed that indeed oligomers of this analogue take a consistent helical structure involving all-trans-amide linkages, independently of the number of residues, from the dimer up to the octamer. Oligomers composed of (R)-β-amino acid units form an extended left-handed helix with about 2.7 residues per turn and an approximately 4.0 Å rise per residue, characterized by complete lack of main-chain hydrogen bonding. This unique helical structure shows some similarity in shape to the trans-amide-based polyproline II (PPII) helix. The present helix was stable in various kinds of solvents such as alcohols. The present work provided a fundamental structural basis for future applications.

Disubstituted adamantane derivative possessing chloropyrazine (1) was synthesized and used as an extended V-shaped host molecule for the preparation of inclusion crystals containing hexyne isomers. The crystallization of 1 with 3-hexyne or 2-hexyne in chloroform provided co-crystals (1a, 1b) with 1:2 host:guest complexation stoichiometry, whereas guest-free crystals (1c) were produced in the case of 1-hexyne. In the co-crystals, the dimers built from 1 through CH···O interaction were arranged into a molecular network through multiple intermolecular interactions, and the guest molecules were accommodated within the cavity built from four molecules of 1. From the crystallization of equimolar binary mixtures of 3-hexyne or 2-hexyne and 1-hexyne in the presence of 1, co-crystals 1a and 1b were supplied, respectively. Competition experiments revealed that the selectivity order of 1 for the hexyne isomers was 3-hexyne and 2-hexyne ≫ 1-hexyne.

Chirality transfer from an α-silylalcohol to α-carbmoyloxy- and α-siloxyallyl-carbanions was investigated using a Brook rearrangement-mediated SE2′ protonation in γ-carbamoyloxy- and γ-siloxy-α-silylallyl alcohols. We proposed a hypothesis that the reaction proceeds along one of two pathways that involves (1) a concerted protonation of a silicate intermediate and (2) a concerted lithiation of the intermediate followed by protonation with retention or by protonation after racemization. Comparison of the extent of the chirality transfer provides a new method for semi-quantitative evaluation of the propensity for racemization of lithiocarbanions next to a conjugative electron-withdrawing group.

Twin-bowl-shaped tris(spiroorthocarbonate) cyclophanes were designed and prepared as ditopic hosts for electrically neutral or electron-rich guests. Preparation of the desired cyclophanes was achieved by cyclotrimerization of 2,2',3,3'-tetrahydroxy-1,1'-binaphthyl (THB) via the transesterification of tetraphenyl orthocarbonate or dichlorodiphenoxymethane. In those reactions, bis(spiroorthocarbonate) cyclophane containing two THB units was also formed as the kinetically favored product. The spiroorthocarbonate twin bowl exhibited ditopic molecular recognition toward fullerene C60 in the crystalline state.

Trisubstituted 5-stibano-1H-1,2,3-triazoles were synthesized in moderate to excellent yields by the Cu-catalyzed [3 + 2] cycloaddition of a ethynylstibane with organic azides in the presence of CuBr (5 mol %) under aerobic conditions. The reaction of 5-stibanotriazole with HCl, I2, and NOBF4 afforded 1-benzyl-4-phenyltriazole, 1-benzyl-5-iodo-4-phenyltriazole, and a pentavalent organoantimony compound, respectively.

Siloxy-N-silylketenimines generated in situ from O-silyl cyanohydrins were converted to α-ketoamides by brief exposure to air or oxygen. Oxidation under extremely mild conditions can be explained by assuming the intermediacy of a 3-imino-1,2-dioxetane derivative generated via triplet–singlet intersystem crossing after the reaction of siloxy-N-silylketenimines with triplet oxygen.