Synthesis of N‐pivot lariat ethers

This review covers the main strategies for the synthesis of N‐pivot lariat ethers as well as their specific syntheses.     

Synthesis of lipophilic crown ethers with pendant carboxylic acid groups

Synthetic routes to thirteen highly lipophilic crown ether carboxylic acids are described. Seven contain 12–15-membered crown ether units with four ring oxygens and are designed for lithium ion complexation. Three others possess large ring 24-crown-8, 27-crown-9, and 30-crown-10 units. Six new hydroxymethyl crown ethers are prepared as synthetic intermediates.     

Synthesis of lipophilic crown ethers with pendant phosphonic acid or phosphonic acid monoethyl ester groups

Synthetic routes to fifteen lipophilic crown ether phosphonic acid monoethyl esters and nine lipophilic crown ether phosphonic acids are described. For both classes of crown ethers which have pendant, protonionizable groups, the crown ether ring sizes are systematically varied from 12-crown-4 and 24-crown-8.     

Synthesis of dibenzocrown ethers with pendant thioamide groups

The synthesis of eighteen crown ether compounds with pendant thioamide, N-alkylthioamide, and N,N-dialkylthioamide groups is reported. The new crown ether compounds are obtained by one-step reactions from the corresponding sym-dibenzo-16-crown-5-oxyacetamides and sym-(propyl)dibenzo-16-crown-5-oxyacetamides with Lawesson's reagent.     

Synthesis of lariat ethers with pendent amine,amide, O‐benzylhydroxamate,and urethane groups

Synthetic routes to twenty‐six new crown ether compounds with pendent amine, amide, O‐benzylhydrox‐amate, and urethane groups are reported. The new lariat ether compounds are based on sym‐dibenzo‐16‐crown‐5, sym‐dicyclohexano‐16‐crown‐5, and 14‐crown‐4 scaffolds.     

Synthesis and characterization of a poly(N‐isopropylacrylamide) with β‐cyclodextrin as pendant groups

A novel linear poly(N‐isopropylacrylamide) (PNIPA) with β‐cylodextrin (β‐CD) moiety (PNIPA‐β‐CD) was synthesized by the conjugation of β‐CD carrying amino groups (EDA‐β‐CD) onto PNIPA with epoxy groups (P(NIPA‐co‐GMA), M_n = 3.86 × 10⁴), and the related reaction conditions are investigated. PNIPA‐β‐CD was characterized by means of IR, NMR and UV spectroscopes, element analysis, and differential scanning calorimetry (DSC). The number‐average molecular weight (M_n) and the β‐CD content of the obtained PNIPA‐β‐CD are 4.87 × 10⁴ and 18.8 wt %, respectively. PNIPA‐β‐CD can not only respond to temperature stimuli but also include guest molecules. Lower critical solution temperature (LCST) of aqueous PNIPA‐β‐CD solution is similar to that of PNIPA. The association constant (K_a) for PNIPA‐β‐CD with methyl orange (MO) is 2.4 × 10³ L mol^?1 at pH 1.4, which is comparable to that of EDA‐β‐CD (K_a = 2.9 × 10³ L mol^?1). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3516–3524, 2005     

Dual responsive poly(N‐isopropylacrylamide) hydrogels having spironaphthoxazines as pendant groups

Stimuli responsive hydrogels (PNIPAAm‐MSp) with a thermoresponsive backbone and photochromic pendant groups were synthesized via free radical polymerization using N‐isopropylacrylamide, modified spironaphthoxazines with a polymerizable double bond (MSp) as photochromic monomer, the crosslinker N,N′‐methylenebis(acrylamide) and the initiator 2,2′‐azobis(isobutyronitrile) in dimethylsulfoxide. The polymers are dual responsive, in that poly(N‐isopropylacrylamide) (PNIPAAm) responds to temperature changes whereas the pendant spironaphthoxazines respond to light. Irradiation enhanced the water absorption of the polymers while increases in temperature decreased it. The irradiated PNIPAAm‐MSp showed best water absorption at 0 °C (Q = 3.25) while water desorbed at higher temperatures (35 °C; Q = 0.30); where Q is the amount of water absorbed by a gram of dry polymer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3318–3325, 2009     

Synthesis and chiroptical properties of L‐valine‐containing poly(phenylacetylene)s with (a)chiral pendant terminal groups

Poly(phenylacetylene)s containing L ‐valine residues (P 1 ) with (a)chiral pendant terminal groups R^(*) [?(HC?C{C₆H₄CONHCH[CH(CH₃)₂]COO? R^(*)})_n?]; R^(*) = 1‐octyl (P 1 o), (1S,2R,5S)‐(+)‐menthyl [P 1 (+)], (1R,2S,5R)‐(?)‐menthyl [P 1 (?)] are designed and synthesized. The polymers are prepared by organorhodium catalysts in high yields (yield up to 88%) with high molecular weights (M_w up to ?6.4 × 10⁵). Their structures and properties are characterized by NMR, IR, TGA, UV, and circular dichroism analyses. All the polymers are thermally fairly stable (T_d ≥ 320 °C). The chiral moieties induce the poly(phenylacetylene) chains to helically rotate in a preferred direction. The chirality of the pendant terminal groups affects little the helicity of the polymers but their bulkiness stabilizes the helical conformation against solvent perturbation. The backbone conjugation and chain helicity of the polymers can be modulated continuously and reversibly by acid. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2117–2129, 2006     

Synthesis and properties of azobenzene‐containing poly(1‐alkyne)s with different functional pendant groups

1‐Alkynes containing azobenzene mesogenic moieties [HC?C(CH₂)₉? O? ph? N?N? ph? O? R; R = ethyl ( 1 ), octyl ( 2 ), decyl ( 3 ), (S)‐2‐methylbutyl ( 4 ), or (S)‐1‐ethoxy‐1‐oxopropan‐2‐yl ( 5 ); ph = 1,4‐phenyl] were synthesized and polymerized in the presence of a Rh catalyst {(nbd)Rh⁺[B(C₆H5)₄]^?; nbd = 2,5‐norbornadiene} to yield a series of liquid‐crystalline polymers in high yields (e.g., >75%). These polymers had moderate molecular weights (number‐average molecular weight ≥ 12,000), high cis contents in the main chain (up to 83%), good thermal stability, and good solubility in common organic solvents, such as tetrahydrofuran, chloroform, and dichloromethane. These polymers were thoroughly characterized by a combination of infrared, nuclear magnetic resonance, thermogravimetric analysis, differential scanning calorimetry, polarized optical microscopy, and two‐dimensional wide‐angle X‐ray diffraction techniques. The liquid‐crystalline behavior of these polymers was dependent on the tail group attached to the azobenzene structure. Poly‐ 1 , which had the shortest tail group, that is, an ethyl group, showed a smectic A mesophase, whereas poly‐ 2 , poly‐ 3 , and poly‐ 5 , which had longer or chiral tail groups, formed smectic C mesophases, and poly‐ 4 , which had another chiral group attached to the azobenzene structure, showed a chiral smectic C mesophase in both the heating and cooling processes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4532–4545, 2006     

Synthesis and characterization of Ni (II) complexes supported by phenoxy/naphthoxy‐imine ligands with pendant N‐ and O‐donor groups and their use in ethylene oligomerization

A series of new Ni(II) complexes of general formula Ni{ZNO} Br ( 2a‐i ) (ZNO = phenoxy/naphthoxy‐imine with pendant N‐ and O‐donor groups) were prepared and characterized by elemental analysis, IR spectroscopy, ESI‐HRMS, and by X‐ray crystallography for 2e . In the solid state, 2e features a monomeric structure with κ³ coordination of the monoanionic naphthoxy‐imine‐quinoline ligand onto the nickel center. Upon activation with MAO, both classes of nickel catalysts were able to produce selectively 1‐butene (81.5–92.1 wt%) with turnover frequencies (TOFs) varying from 3,100 to 24,300 mol(C₂H₄) mol (Ni)^?1 h^?1. Nickel precatalysts bearing phenoxy‐imine ligands were much more active than its naphthoxy analogous under the same conditions. The use of a mixture of cocatalysts (MAO/TMA or MAO/TiBA) resulted in poor activities; however the presence of TiBA in the milieu led to a significant improvement on selectivity for 1‐hexene (25.5 wt%). Under optimized conditions ([Ni] = 10 μmol, 30 °C, oligomerization time = 5 min, 20 bar ethylene, [Al]/[Ni] = 600), precatalyst 2c led to TOF = 59,900 mol(C₂H₄) mol(Ni)^?1 h^?1 and selectivity for 1‐butene of 89.5 wt%.     

Synthesis and Antitubercular Evaluation of N‐Arylpyrazine and N,N′‐Alkyl‐diylpyrazine‐2‐carboxamide Derivatives

Two series of pyrazinamide (PZA) derivatives have been synthesized and evaluated for their in vitro antibacterial activity against Mycobacterium tuberculosis H37Rv. Some compounds exhibited minimum inhibitory concentration activity of 50–100 μg/mL, greater than the first line antituberculosis drug PZA in Alamar Blue assay (>100 μg/mL). The obtained activities can be considered promising results, which characterizes these compounds as good start points to development of new antitubercular agents.     

Novel crown ethers with pendant,proton-ionizable,chromogenic groups

Synthesis of fifteen new chromogenic crown ethers is described in which one phenyl group of diphenylamine has been substituted at the 2-, 4-, and 6-positions with strongly electron-withdrawing groups and the other phenyl group bears an oxymethyl crown ether substituent. Structural variations include the crown ether ring size, identity of the electron-withdrawing groups, acidity of the amine function, and positioning of the oxymethyl crown ether substituent ortho, meta, and para to the amine nitrogen. Preparation of a structurally-related chromogenic bis(crown ether) is also reported.     

Synthesis,characterization and hydroformylation activity of 7‐azaindolate‐bridged dinuclear rhodium(I)phosphines with pendant polar‐groups

New dinuclear Rh(I)–Phosphines of the types [Rh(µ‐azi)(CO)(L)]₂ ( 1,3 – 7 ) and [Rh(µ‐azi)(L)]₂ ( 8 ) with pendant polar groups, and a chealated mononuclear compound [Rh(azi‐H)(CO)(L)] ( 2 ) (where azi = 7‐azaindolate, L = polar phosphine) were isolated from the reaction of [Rh(µ‐Cl)(CO)₂]₂ with 7‐azaindolate followed by some polar mono‐ and bis‐phosphines ( L ₁ – L ₈ ). A relationship between Δδ³¹P‐NMR and ν(CO) values was considered to define the impact of polar‐groups on σ‐donor properties of the phosphines. These compounds were evaluated as catalyst precursors in the hydroformylation of 1‐hexene and 1‐dodecene both in mono‐ and biphasic aqueous organic systems. While the biphasic hydroformylations (water + toluene) gave exclusively the aldehydes, the monophasic one (aqueous ethanol) showed propensity to form both aldehydes and alcohols. The influence of bimetallic cooperative effects, and σ‐donor and hydrophilic properties of the phosphines with pendant polar‐groups in enhancing the yields and selectivity of hydroformylation products was emphasized. In addition, when strong σ‐donor phosphine was used, the π‐acceptor nature of pyridine ring of 7‐azaindolate spacer was found to be a considerable factor in facilitating the facile cleavage of CO group during hydroformylation and in supplementing the cooperative effects. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of dibenzo‐16‐crown‐5 compounds with pendant ester and ether groups

Structurally related dibenzo‐16‐crown‐5 lariat ethers with pendant ester and ether groups are prepared. Structural variations within the series of alkyl lariat ether esters include changes in the O‐alkyl group, attachment site and nature of the lipophilic group, and length of the spacer, which connects the ester group to the polyether framework. Also synthesized are bis(crown ether) diesters with two dibenzo‐16‐crown‐5 or two dicyclohexano‐16‐crown‐5 units and two ester groups connected to each other by a linker of varying length. Synthetic strategies for the preparation of these lariat ethers with pendant ester‐ and ether‐containing side arms are described.     

Lone-pair activity in lead(II) complexes with unsymmetrical lariat ethers

We have carried out a study about the structural effect of the lone-pair activity in lead(II) complexes with the unsymmetrical lariat ethers L(7), L(8), (L(8)-H)-, (L(9)-H)-, and (L(10)-H)-. All these ligands are octadentate and differ by the aromatic unit present in their backbones: pyridine, phenol, phenolate, thiophenolate, and pyrrolate, respectively. In these lead(II) complexes, the receptor may adopt two possible syn conformations, depending on the disposition of the pendant arms over the crown moiety fragment. The conformation where the pendant arm holding the imine group is placed above the macrocyclic chain containing two ether oxygen atoms has been denoted as I, whereas the term II refers to the conformation in which such pendant arm is placed above the macrocyclic chain containing the single oxygen atom. Compounds of formula [Pb(L(7))](ClO4)2 (1) and [Pb(L(8)-H)](ClO4) (2) were isolated and structurally characterized by X-ray diffraction analyses. The crystal structure of 1 adopts conformation I and shows the lead(II) ion bound to the eight available donor atoms of the bibracchial lariat ether in a holodirected geometry, whereas the geometry of 2 is best described as hemidirected, with the receptor adopting conformation II. The five systems [Pb(L(7))]2+, [Pb(L(8))]2+, [Pb(L(8)-H)]+, [Pb(L(9)-H)]+, and [Pb(L(10)-H)]+ were characterized by means of density functional theory calculations (DFT) performed by using the B3LYP model. An analysis of the natural bond orbitals (NBOs) indicates that the Pb(II) lone-pair orbital remains almost entirely s in character in the [Pb(L(7))]2+ complexes, whereas in [Pb(L(8)-H)]+, the Pb(II) lone pair is polarized by a certain 6p contribution. The reasons for the different roles of the Pb(II) lone pair in compounds 1 and 2 as well as in the related model compounds are discussed. Our results point to the presence of a charged donor atom in the ligand (such as a phenolate oxygen atom, pyrrolate nitrogen atom, or even thiophenolate sulfur atom) favoring hemidirected geometries.     

Synthesis of new thermosetting poly(2,6‐dimethyl‐1,4‐phenylene oxide)s containing epoxide pendant groups

A new class of thermosetting poly(2,6‐dimethyl‐1,4‐phenylene oxide)s containing pendant epoxide groups were synthesized and characterized. These new epoxy polymers were prepared through the bromination of poly(2,6‐dimethyl‐1,4‐phenylene oxide) in halogenated aromatic hydrocarbons followed by a Wittig reaction to yield vinyl‐substituted polymer derivatives. The treatment of the vinyl‐substituted polymers with m‐chloroperbenzoic acid led to the formation of epoxidized poly(2,6‐dimethyl‐1,4‐phenylene oxide) with variable pendant ratios, and the structures and properties were studied with nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and gel permeation chromatography. The ratios of pendant functional groups were tailored for the polymer properties, and the results showed that the glass‐transition temperatures increased as the benzylic protons were replaced by bromo‐, vinyl‐, or epoxide‐functional groups, whereas the thermal stability decreased in comparison with the original polymer. Within a molar fraction of 20–50%, the degree of functionalization had little effect on the glass‐transition temperature; however, it correlated inversely with the thermal stability of each functionalized polymer. The thermal curing behavior of the epoxide‐functionalized polymer was enhanced by the increment of the pendant functionality, which resulted in a significant increase in the glass‐transition temperature as well as the thermal stability after the curing reaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5875–5886, 2006     

Synthesis and optical properties of novel blue‐light‐emitting poly(p‐phenylene vinylene) derivatives with pendant oxadiazole or cyano groups

Two novel poly(p‐phenylene vinylene) polymers, which carried side substituents with cyano groups or 1,3,4‐oxadiazole, were synthesized by Heck coupling. They consisted of alternating conjugated segments and nonconjugated aliphatic spacers. The polymers had moderate molecular weights, were amorphous, and dissolved readily in tetrahydrofuran and halogenated organic solvents. They were stable up to approximately 340 °C in N₂ and 290 °C in air, and the anaerobic char yield was around 60% at 800 °C. The polymer with cyano side groups emitted blue light in solutions and thin films with identical photoluminescence (PL) maximum at 450 nm; this supported the idea that chain interactions were hindered even in the solid state. The PL maximum of this polymer in thin films was blueshifted upon annealing at 120 °C, indicating a thermochromic effect as a result of conformational changes in the polymer backbone. The polymer containing side substituents with oxadiazole rings emitted blue light in solutions with a PL maximum at 474 nm and blue‐greenish light in thin films with a PL maximum at 511 nm. The PL quantum yields of the polymers in tetrahydrofuran were 0.13–0.24. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1768–1778, 2004     

Synthesis and hydrophobic association of poly(N,N‐dimethylacrylamide) end‐functionalized with perfluorocarbon and hydrocarbon groups

Polydimethylacrylamides (PDMAs) end‐functionalized with hydrophobic groups were synthesized by the reaction of cesium salts of one‐ or two‐ended living PDMA anion with octadecanoyl and perfluorooctanoyl chlorides and with α‐phenylacrylate monomers containing an octadecyl group attached via oligooxyethylene spacers to the acrylate functionality. Size exclusion chromatography or NMR studies indicated that the end functionalizations were nearly quantitative. Reduced viscosity measurements were consistent with predominantly dimeric association of the perfluorooctanoyl‐end‐functionalized PDMAs. The association of the two‐ended, perfluorooctanoyl‐ and octadecanoyl‐functionalized polymers was more extensive and consistent with pairwise association. Furthermore, the presence of oligoethylene oxide spacers between the octadecyl and α‐phenylacrylate groups greatly enhanced the hydrophobic association of bis(octadecyl)‐end‐functionalized PDMA. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1403–1418, 2001     

Synthesis of phenylquinoxaline oligomers containing pendant electron‐donating and electron‐withdrawing groups

A series of extended 6‐substituted quinoxaline AB monomer mixtures, 2‐(4‐fluorophenyl)‐3‐[4‐(4‐hydroxyphenoxy)phenyl]‐6‐substituted quinoxaline and 3‐(4‐fluorophenyl)‐2‐[4‐(4‐hydroxyphenoxy)phenyl]‐6‐substituted quinoxaline, were prepared and polymerized to afford phenylquinoxaline oligomers. High‐molecular‐weight polymers could not be obtained because of the formation of cyclic oligomers. On the basis of matrix‐assisted laser desorption/ionization time‐of‐flight analysis and molecular modeling results, the formation of a cyclic dimer could be a favorable process resulting in low‐molecular‐weight oligomers. They were completely soluble and amorphous, with glass‐transition temperatures varying from 165 to 266 °C, and they had thermooxidative stability, with samples displaying 5% weight loss temperatures of 419–511 °C in nitrogen. The thermal properties of the monomers and resultant polymers dramatically depended on the polarity of the substituents. The monomers and resultant oligomers displayed high fluorescence in tetrahydrofuran solutions and N‐methyl‐2‐pyrrolidinone solutions, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6465–6479, 2005