Folding-promoted TBACl-mediated chemo- and regioselective demethylations of methoxybenzene-based macrocyclic pentamers

Tetrabutylammonium chloride (TBACl) salt alone has not been shown previously to be capable of removing methoxy groups. It is demonstrated here that the use of TBACl achieves efficient folding-promoted chemo- and regioselective demethylations, eliminating up to two out of five methyl groups situated in similar macrocyclic chemical microenvironments.     

Highly selective one-pot synthesis of H-bonded pentagon-shaped circular aromatic pentamers

One-pot, multi-molecular macrocyclization allows the highly selective preparation of pentagon-shaped circular aromatic pentamers mediated by an inward-pointing continuous hydrogen-bonding network.     

Five-fold-symmetric macrocyclic aromatic pentamers: high-affinity cation recognition, ion-pair-induced columnar stacking, and nanofibrillation

Described in this study is a conceptually new class of five-fold-symmetric cavity-containing planar pentameric macrocycles with their interior decorated by five convergently aligned, properly spaced carbonyl oxygen atoms. These cation-binding oxygens enclose a hydrophilic lumen of 2.85 ? in radius and thus display high-affinity binding toward alkali metal cations, and possibly many other cations, too. Arising from their high-affinity recognition of metal ions, these planar macrocycles form cation- or ion-pair-induced one-dimensional columnar aggregates, and subsequently fascinating fibrillation results.     

BOP-mediated one-pot synthesis of C5-symmetric macrocyclic pyridone pentamers

We report here, for the first time, the BOP-mediated one-pot macrocyclization that is facilitated and guided by internally placed intramolecular H-bonds to allow for the highly selective formation of five-residue cation-binding macrocycles.     

One-pot synthesis of hybrid macrocyclic pentamers with variable functionalizations around the periphery

Rather than four- or six-residue macrocylces, one-pot macrocyclization allows for the highly selective formation of five-residue macrocycles rigidified by intramolecular hydrogen bonds. Variable functionalizations around the pentameric periphery were achieved by reacting monomers with higher oligomers bearing different exterior side chains. The formation of these hybrid pentamers suggests a chain-growth mechanism for the one-pot macrocyclization where the successive addition of monomers onto higher oligomers is faster than those between two monomers or two higher oligomers.     

POCl3-mediated H-bonding-directed one-pot synthesis of macrocyclic pentamers, strained hexamers and highly strained heptamers

Previously we have shown that POCl3-mediated H-bonding-directed one-pot macrocyclization allows for the highly selective preparation of five-residue macrocycles as the predominant product with low yields of hexamers and an undetectable occurrence of both tetramers and heptamers.Replacing the interiorly arrayed methyl groups with ethyl groups in these 4-7 residue macrocycles alters the relative stability order among them.Specifically,ethoxy-substituted six-residue macrocycle,rather than pentamer,turns out to be computationally the most stable,suggesting that ethoxy-containing hexamer possibly can be formed as the major product under suitable conditions.We have investigated this possibility by varying reaction temperatures and concentrations,invariably affording pentamer as the major macrocycle with strained circular hexamers and highly strained circular heptamers produced in substantial amounts.This discrepancy can be reasonably explained on the basis of bimolecular reactions between two oligomers higher than monomers via kinetic simulations.In this scenario,the acyclic pentamer is kinetically "trapped" to undergo an intramolecular cyclization to yield circular pentamer,rather than to produce acyclic hexamer.As a result,acyclic hexamer precursor is generated largely from sterically demanding bimolecular reactions between a dimer and a tetramer,or between two trimers that are kinetically slower than the pentamer-producing chain-growth reactions.We additionally found that one-pot macrocyclization proceeds to the largest extent at 40 ℃,an intriguing finding that highlights the low reactivities of acid chloride and amine groups in these H-bond-enforced acyclic oligomeric intermediates.     

Synthesis and characterization of macrocyclic vinyl aromatic polymers

The synthesis and characterization by size exclusion chromatography, liquid chromatography, NMR, matrix‐assisted laser desorption/ionization, thermal analysis, and other techniques of well‐defined and narrow molecular weight distribution macrocyclic polystyrene (PS), poly(2‐vinylpyridine), poly(α‐methylstyrene), poly (2‐vinyl‐naphthalene) (P2VN), and poly(9,9‐dimethyl‐2‐vinylfluorene) (PDMVF) containing a single 1,4‐benzylidene, methylidene, or 9,10‐anthracenylidene unit are reviewed. The absorption and emission spectroscopy of PS, P2VN, and PDMVF is also discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2139–2155, 2006     

Folding-promoted methylation of a helical DMAP analogue

The methylation rate for a series of pyridine-containing phenylene ethynylene oligomers shows a nonlinear dependence on chain length, with a significant rate enhancement observed for oligomers that adopt a folded, helical conformation. The folded structure provides a microenvironment that lowers the energy barrier for the methylation reaction. Of these noncovalent interactions, the largest stabilization may arise from binding of methyl iodide in the hydrophobic cavity of the folded oligomer, in close proximity to the pyridine nucleophile.     

Cesium fluoride assisted synthesis of macrocyclic polyethers with aromatic subunits

Several features of the synthesis of crown ethers with aromatic subunits by reactions of dihydroxyaromatic or bis(hydroxyaromatic) compounds with cesium fluoride and polyethylene glycol tosylates are explored. The method is utilized to prepare several new crown ethers and to synthesize known crown compounds in improved yields.     

Anthracene-based macrocyclic fluorescent chemosensor for selective sensing of dicarboxylate

An anthracene-based macrocyclic receptor has been designed and synthesized for selective recognition of 1,4-phenylenediacetate (K_a = 3.34 × 10⁵ M^?1). The macrocycle binds 1,4-phenylenediacetate selectively at the charged sites of the receptor with a concomitant increase in fluorescence of anthracene. The interaction properties of the macrocycle were evaluated by ¹H NMR, UV–vis and fluorescence spectroscopic methods.     

Synthesis and thermal and spectroscopic properties of macrocyclic vinyl aromatic polymers

Well‐defined and narrow molecular weight distribution macrocyclic poly(2‐vinylnaphthalene) (P2VN) and poly(2‐vinyl‐9,9‐dimethylfluorene) (PDMVF) containing a single 1,4‐benzylidene or 9,10‐anthracenylidene unit have been synthesized via the potassium naphthalide initiated polymerization of the monomers followed by the end‐to‐end coupling of the resulting P2VN dianions under high‐dilution conditions with 1,4‐bis(bromomethyl)benzene or 9,10‐bis(chloromethyl)anthracene. Molecular characterization has been carried out by size exclusion chromatography, nuclear magnetic resonance, differential scanning calorimetry, ultraviolet–visible spectroscopy, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. The thermal properties show distinct differences between the cyclic and matching linear polymers, with the macrocycles showing much higher glass‐transition and decomposition temperatures. The absorption bands are both hyperchromic and hypochromic with respect to the model aromatic compounds, and this is consistent with intensity borrowing. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5488–5503, 2004     

Sulfone-linked paracyclophanes via macrocyclic aromatic thioethers: synthetic and structural investigations

Reaction of 4,4'-sulfonylbis(benzenethiol) with 4,4'-dichlorodiphenylsulfone under pseudo-high-dilution conditions leads to macrocyclic thioethersulfones [-S-Ar-SO2-Ar-]n (Ar = 1,4-phenylene). These include a highly strained [1+1] cyclodimer (n = 2), a cyclotrimer resulting from thioetherexchange reactions, and a [2+2] cyclotetramer which can adopt two entirely different conformations in the crystalline state, one having molecular D2d ("tennis-ball-seam") symmetry. The same type of reaction is successful using 4,4'-thiobis(benzenethiol) instead of 4,4'-sulfonylbis(benzenethiol) and affords macrocycles with a higher ratio of thioether to sulfone linkages. Exhaustive oxidation of macrocyclic thioethersulfones with hydrogen peroxide affords a series of sulfone-linked paracyclophanes, [-Ar-SO2-]4, [-Ar-SO2-]6, [-Ar-SO2-]8 and [-Ar-SO2-]12. Single crystal X-ray analysis reveals [Ar-SO2-]4 to be a near-perfect square box, whilst the cyclic hexamer [-Ar-SO2-]6 adopts a much more irregular conformation. and [-Ar-SO2-]8 displays a "double-box" structure clearly related to that of [Ar-SO2-]4.     

Towards the selective synthesis of macrocyclic vinyl polymers of controlled size

A new strategy for the synthesis of vinyl type macrocyclic polymers of controlled molecular weight and molecular weight distribution has been investigated. It involves the direct coupling of an α-ω-heterodifunctional linear polymer precursor previously prepared by living polymerization. The cyclization is achieved under high dilution, by an appropriate activation of one of the polymer-ends in order to allow its reaction with the other end function. Its application to the preparation of polystyrenes and poly(vinyl ether)s with a macrocyclic structure, as well as ring closure mechanisms in the presence of different cyclization agents are reported.     

Chiral porphyrin dimer with a macrocyclic cavity for intercalation of aromatic guests

Chiral diporphyrin receptor 1, which has a macrocyclic cavity to sandwich aromatic guest molecules via double π-π stacking interactions, enabled the naked-eye detection of an aromatic explosive as well as chiral discrimination in NMR.     

二十四元六氮大环双核铜(I)配合物的氧化去甲基作用: 单加氧酶的模拟

以5-溴-2-甲氧基-1, 3-苯二甲醛与二乙烯三胺通过[2+2]缩合,合成了一个新的六氮杂二十四元大环配体, 并在[Cu(CH3CN)4]ClO4存在下生成Cu(I)大环配合物, 然后在空气(或氧气)中氧化, 得到了新的大环双核Cu(II)配合物, 用多种方法对其进行了表征, 用1H NMR谱等方法鉴定了氧化产物。实验结果表明: 在Cu(I)配合物氧化过程中,能使配体环上的一个甲氧基发生断裂, 形成苯氧桥和水桥联的Cu(II)配合物。在木质素酶等单加氧酶的氧化过程中也伴随着氧化去甲基作用。本文首次用大环配合物对这一过程进行了模拟, 并测定了氧化反应中的吸氧量和吸氧速率常数。     

Spectroscopic observation of nitrous oxide pentamers

Two new infrared bands in the ν(1) fundamental region of N(2)O are observed in a supersonic jet expansion and assigned to nitrous oxide pentamers. Each band is measured using both (14)N(2)(16)O and (15)N(2)(16)O. Although they are similar in appearance, the bands have slightly different lower state rotational parameters, and are thus assigned to distinct structural isomers of the pentamer. Cluster calculations using two N(2)O intermolecular potentials give results in good agreement with the observed spectra, and indicate that the two isomers probably have the same basic structure (which is unsymmetrical), but differ in the alignment (N-N-O or O-N-N) of one or two of the constituent monomers. Calculations using a resonant dipole interaction model also support the proposed assignment and structure. These are the first reported high-resolution spectra for N(2)O pentamers.     

Construction of macrocyclic structure using conformational properties of secondary and tertiary aromatic amides

A large macrocyclic compound with six para-phenylene rings and six amide moieties, which are alternately secondary and tertiary, was synthesized. In a stepwise synthesis, the final cyclization step was successful because a combination of three tertiary amides, which prefer a cis conformation, and two linear secondary amides would arrange both amino and carboxyl ends close to each other, while various sizes of macrocyclic compounds including the target cyclic trimer were generated in one-pot synthesis where three secondary amide bonds were formed.