Synthesis and photoreactivity of aryl substituted 4,5-dithienyl[1,3]dithiol-2-ones

UV irradiation of hitherto unknown 4,5-bis-benzol[b]thiophen-3-yl-[1,3]dithiol-2-one gave 3-(3-benzo[b]thienyl)-thieno[3,4-c]benzo[ e][1,2]dithine by loss of carbon monoxide and rearrangement, whereas 4,5-bis-(2-bromo-phenyl)-[1,3]dithiol-2-one gave a polymeric material containing S-S bridges. The Structures of both photoproducts were demonstrated on the basis of chemical behaviour and/or X-ray diffraction. (C) 2009 Elsevier Ltd. All rights reserved.

Alternative syntheses of linear polyurethanes using masked isocyanate monomers

A range of linear polyurethanes featuring aliphatic, aromatic and ether residues have been prepared by co-polymerisation of novel 'masked' isocyanate A(2)-type monomers and diols. The reactive isocyanate monomers were generated in situ via the triphenylphosphine mediated decomposition of the heterocyclic disulfide, 1,2,4-dithiazolidine-3,5-dione. Two different synthetic approaches were examined and assessed for the construction of the novel A(2)-type monomers, which involved either coupling two 1,2,4-dithiazolidine-3,5-diones together through a spacer group or construction of 1,2,4-dithiazolidine-3,5-diones directly from diamines. The resulting polyurethanes were purified via solvent extraction and analysed using GPC, NMR and IR spectroscopic analyses. Molecular weight data were obtained and compared from both GPC and H-1 NMR (via end-group analysis) spectroscopic analysis. The thermal properties of the polyurethanes were determined using DSC and their solubility in common aprotic organic solvents was also assessed and related to their structural composition. (c) 2006 Elsevier B.V. All rights reserved.

Surface modification of nylon 6,6 using a carbene insertion approach

The diazirine functionalised fluorenone, 3-[3-(trifluoromethyl)diazirin-3-yl]phenyl-9-oxo-9H-fluorene-2-carboxyla te was synthesised to act as a model compound capable of modifying a wide variety of polymeric substrates. Photochemical activation of the diazirine moiety of the fluorenone derivative was utilised to afford highly reactive carbenes capable of insertion into or addition to a wide variety of functionalities. In this paper the photoinduced attachment of a fluorenone derivative to nylon 6,6 has been studied using UV-visible spectroscopic analysis. Incorporation of the fluorenone chromophore onto the backbone of nylon at different loading levels and after different coating cycles has been investigated and is detailed in this paper.

Asymmetric synthesis of (1R,2S,3R)-3-methylcispentacin and (1S,2S,3R)-3-methyltranspentacin by kinetic resolution of tert-butyl (+/-)-3-methylcyclopentene-1-carboxylate

Conjugate addition of lithium dibenzylamide to tert-butyl (+/-)-3-methylcyclopentene-1-carboxylate occurs with high levels of stereocontrol, with preferential addition of lithium dibenzylamide to the face of the cyclic alpha,beta-unsaturated acceptor anti- to the 3-methyl substituent. High levels of enantiorecognition are observed between tert-butyl (+/-)-3-methylcyclopentene-1-carboxylate and an excess of lithium (+/-)-N-benzyl-N-alpha-methylbenzylamide (10 eq.) (E > 140) in their mutual kinetic resolution, while the kinetic resolution of tert-butyl (+/-)-3-methylcyclopentene-1-carboxylate with lithium (S)-N-benzyl-N-alpha-methylbenzylamide proceeds to give, at 51% conversion, tert-butyl (1R, 2S, 3R,alphaS)-3-methyl-2-N-benzyl-N-alpha-methylbenzylaminocyclopentane-1-c arboxylate consistent with E > 130, and in 39% yield and 99 +/- 0.5% de after purification. Subsequent deprotection by hydrogenolysis and ester hydrolysis gives (1R, 2S, 3R)-3-methylcispentacin in > 98% de and 98 +/- 1% ee. Selective epimerisation of tert-butyl (1R, 2S, 3R, alphaS)-3-methyl-2-N- benzyl-N-alpha-methylbenzylaminocyclopentane-1-carboxylate by treatment with (KOBu)-Bu-t in (BuOH)-Bu-t gives tert-butyl (1S, 2S, 3R, alphaS)-3-methyl-2-N-benzyl-N-alpha-methylbenzylaminocyclopentane-1-carb oxylate in quantitative yield and in > 98% de, with subsequent deprotection by hydrogenolysis and ester hydrolysis giving (1S, 2S, 3R)-3-methyltranspentacin hydrochloride in > 98% de and 97 +/- 1% ee.

Double coupling reactions of 3,4-bis(stannyl)furanone: facile preparation of diaryl- and dibenzylfuranones

The palladium-catalyzed cross-coupling reaction of 3,4-bis(tributylstannyl)furan-2(5H)-one using chelating ligand or polar solvent gives mixtures of single and double coupled products, even when one equivalent of halide coupling partner is used. After optimization, the double coupling reaction was shown to be general, with the use of two equivalents of aryl iodides giving 3,4-disubstituted furanones, The reaction using benzyl bromides proceeds at lower temperatures than the corresponding coupling using aryl iodides, giving dibenzylfuranones. The methodology has been exemplified in a synthesis of (+/-)-hinokinin.

Crystal and molecular structure of the thioether-analogue of PEEK from X-ray powder data and diffraction-modelling

Analysis of X-ray powder data for the melt-crystallisable aromatic poly(thioether thioether ketone) [-S-Ar-S-Ar-CO-Ar](n), ('PTTK', Ar= 1,4-phenylene), reveals that it adopts a crystal structure very different from that established for its ether-analogue PEEK. Molecular modelling and diffraction-simulation studies of PTTK show that the structure of this polymer is analogous to that of melt-crystallised poly(thioetherketone) [-SAr-CO-Ar](n) in which the carbonyl linkages in symmetry-related chains are aligned anti-parallel to one another. and that these bridging units are crystallographically interchangeable. The final model for the crystal structure of PTTK is thus disordered, in the monoclinic space group 121a (two chains per unit cell), with cell dimensions a = 7.83, b = 6.06, c = 10.35 angstrom, beta = 93.47 degrees. (c) 2005 Elsevier Ltd. All rights reserved.

Dithioacetalisation of PEEK: a general technique for the solubilisation and characterisation of semi-crystalline aromatic polyketones

The family of semi-crystalline, aromatic, high-temperature thermoplastics known as poly(ether-ketone)s are insoluble in conventional organic solvents, but undergo completely general and quantitatively reversible reactions with alkanedithiols in strong acid media, to give soluble poly(dithioacetal)s, which are readily characterisable by GPC and light scattering techniques.

Extreme complementarity in a macrocycle-tweezer complex

Interaction of a novel pyrene-based tweezer molecule with a macrocyclic ether-imide-sulfone results in formation of a strongly bound complex (K-a = 24 000 M-1) in which binding results not only from pi-pi stacking interactions involving pyrene units as donors and macrocyclic naphthalene-tetracarboximide and biphenylenedisulfone groups as acceptors but also from N-(HO)-O-... and C-(HO)-O-... hydrogen bonds and from "reverse" pi-stacking of the electron-poor isophthaloyl residue of the tweezer with an electron-rich 3-aminophenoxy residue of the macrocyclic imide.

Synthesis of strained macrocyclic biaryls for enthalpy-driven ring-opening polymerization

Polymerizable macrocyclic biarylene-ether-ketones and biarylene-ether-sulfones are accessible from linear, bis(chloro)-terminated oligomers via nickel-catalyzed, intramolecular coupling under pseudo-high-dilution conditions. Single-crystal X-ray analyses of the resulting cyclo-oligomers reveal extremely distorted and highly strained geometries, with 4,4 '-biphenylene units showing deviations of up to 70 degrees from linearity.

Spontaneous ring-opening polymerization of macrocyclic aromatic thioether ketones under transient high-temperature conditions

Spontaneous ring-opening polymerization of macrocyclic aromatic thioether ketones [-1,4-SC6H4CO-C6H4-](n) (n = 3 and 4), in which the thioether linkages are para to the ketone, occurs during rapid, transient heating to 480degreesC, to afford a soluble, semi-crystalline poly(thioether ketone) of high molar mass (eta(inh) > 1.0 dL . g(-1)). Corresponding macrocyclic ether ketone, and a macrocyclic thioether ether ketone in which the thioether linkage is para to the ether rather than to the ketone, show no evidence of polymerization under analogous conditions.

Protonation of phenylboronic acid: comparison of G3B3 and G2MP2 methods

G3B3 and G2MP2 calculations using Gaussian 03 have been carried out to investigate the protonation preferences for phenylboronic acid. All nine heavy atoms have been protonated in turn. With both methodologies, the two lowest protonation energies are obtained with the proton located either at the ipso carbon atom or at a hydroxyl oxygen atom. Within the G3B3 formalism, the lowest-energy configuration by 4.3 kcal . mol(-1) is found when the proton is located at the ipso carbon, rather than at the electronegative oxygen atom. In the resulting structure, the phenyl ring has lost a significant amount of aromaticity. By contrast, calculations with G2MP2 show that protonation at the hydroxyl oxygen atom is favored by 7.7 kcal . mol(-1). Calculations using the polarizable continuum model (PCM) solvent method also give preference to protonation at the oxygen atom when water is used as the solvent. The preference for protonation at the ipso carbon found by the more accurate G3B3 method is unexpected and its implications in Suzuki coupling are discussed. (C) 2006 Wiley Periodicals, Inc.

Square planar mononuclear Pd(II) complexes of substituted 2-(pyrazole-1-yl)phenylamines with a helical twist

X-ray crystal structure shows that 3,5-dimethyl-1-(2-nitrophenyl)-1H-pyrazole (DNP) belongs to the rare class of helically twisted synthetic organic molecules. Hydrogenation of DNP gives 2-(3,5-dimethylpyrazole-1-yl)phenylamine (L) which on methylation yields [2-(3,5-dimethylpyrazole-1-yl)phenyl]dimethylamine (L'). Two Pd(II) complexes, PdLCl2 (1) and PdL'Cl-2 (2), are synthesized and characterized by NMR. X-ray crystallography reveals that 1 and 2 are unprecedented square planar complexes which possess well discernible helical twists. (C) 2007 Elsevier B.V. All rights reserved.

Selectivity of bis(calix[4]diquinone) ionophores towards metal ions in solvent dimethylsulfoxide: a molecular mechanics and molecular dynamics study

Molecular modelling studies have been carried out on two bis(calix[4]diqu(inone) ionophores, each created from two (calix[4]diquinone)arenes bridged at their bottom rims via alkyl chains (CH2)(n), 1: n = 3, 2; n = 4, in order to understand the reported selectivity of these ligands towards different sized metal ions such as Na+, K+, Rb+, and Cs+ in dmso solution. Conformational. analyses have been carried out which show that in the lowest energy conformations of the two macrocycles, the individual calix[4]diquinones exhibit a combination of partial cone, 1,3-alternate and cone conformations. The interactions of these alkali metals with the macrocycles have been studied in the gas phase and in a periodic box of solvent dmso by molecular mechanics and molecular dynamics calculations. Molecular mechanics calculations have been carried out on the mode of entry of the ions into the macrocycles and suggest that this is likely to occur from the side of the central cavity, rather than through the main axis of the calix[4]diquinones. There are energy barriers of ca. 19 kcal mol(-1) for this entry path in the gas phase, but in solution no energy barrier is found. Molecular dynamics simulations show that in both 1 and 2, though particularly in the latter macrocycle, one or two solvent molecules are bonded to the metal throughout the course of the simulation, often to the exclusion, of one or more of the ether oxygen atoms. By contrast the carbonyl oxygen atoms remain bonded to the metal atoms throughout with bond lengths that remain significantly less than those to the ether oxygen atoms. Free energy perturbation studies have been carried out in dmso and indicate that for 1, the selectivity follows the order Rb+ approximate to K+ > Cs+ >> Na+, which is partially in agreement with the experimental results. The energy differences are small and indeed the ratio between stability constants found for Cs+ and K+ complexes is only 0.60, showing that 1 has only a slight preference for K+. For the larger receptor 2, which is better suited to metal complexation, the binding affinity follows the pattern Cs+ >> Rb+ >> K+ >> Na+, with energy differences of 5.75, 2.61, 2.78 kcal mol(-1) which is perfectly consistent with experimental results.

Polymer-supported nitroxyl catalysts for selective oxidation of alcohols

Novel non-toxic poly(ethylene glycol)-supported 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) moieties are demonstrated to give an excellent interfacial catalysis for the selective oxidation of alcohols to the corresponding carbonyl species in biphasic media and investigation for the recovery of these new macromolecular catalysts via precipitation with diethyl ether after catalysis has also been briefly studied.

Poly(ethylene glycol)-supported nitroxyls: branched catalysts for the selective oxidation of alcohols

Nitroxyl radicals such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) are highly selective oxidation catalysts for the conversion of primary alcohols into the corresponding aldehydes. In this study, direct tethering of TEMPO units onto linear poly(ethylene glycol) (PEG) has afforded macromolecular catalysts that exhibit solubility in both aqueous and organic solvents. Recovery of the dissolved polymer-supported catalyst has been carried out by precipitation with a suitable solvent such as diethyl ether. The high catalyst activities and selectivities associated traditionally with nitroxyl-mediated oxidations of alcohols are retained by the series of "linker-less" linear PEG-TEMPO catalysts in which the TEMPO moiety is coupled directly to the PEG support. Although the selectivity remains unaltered, upon recycling of the linker-less polymer-supported catalysts, extended reaction times are required to maintain high yields of the desired carbonyl compounds. Alternatively, attachment of two nitroxyl radicals onto each functionalized PEG chain terminus via a 5-hydroxyisophthalic acid linker affords branched polymer-supported catalysts. In stark contrast to the linker-less catalysts, these branched nitroxyls exhibit catalytic activities up to five times greater than 4-methoxy-TEMPO alone under similar conditions. In addition, minimal decrease in catalytic activity is observed upon recycling of these branched macromolecular catalysts via solvent-induced precipitation. The high catalytic activities and preservation of activity upon recycling of these branched systems is attributed to enhanced regeneration of the nitroxyl species as a result of intramolecular syn-proportionation.