Tetrasubstituted Biphenyls Research Articles

Lithium/Element Exchange as an Efficient Tool for Accessing Atropo-enriched Biaryls via Arynes.

This account documents the development of transition metal-free, aryne-mediated aryl-aryl coupling, the 'ARYNE coupling', which began in 2001 in Lausanne. ortho,ortho'-Di-, tri- and even tetrasubstituted biphenyls have now become accessible on a multi-gram scale. The reaction is perfectly regioselective and the obtained polybromobiphenyls can be submitted to regioselective bromine/lithium interconversions. The access to enantiopure biphenyls is now possible using enantiopure sulfoxides as chiral auxiliaries, which allow for subsequent chemoselective sulfoxide/metal exchange on each atropo-diastereoisomer with configurational stability of the intermediate biaryllithiums. Direct atropo-diastereoselective ARYNE coupling has been reported more recently.

Direct C-H arene homocoupling over gold nanoparticles supported on metal oxides.

The direct CH/CH bond coupling of dimethyl phthalate was performed successfully over supported gold nanoparticle catalysts. Gold on reducible metal oxides, such as Co3 O4 , and on inert oxides that have an oxygen-releasing capacity, such as ZrO2 , showed the highest catalytic activity for the production of biphenyl tetracarboxylate using O2 as the sole oxidant. Supported Pd(OH)2 also catalyzed the reaction, but the catalytic activity was inferior to that of gold. Moreover, the gold catalysts exhibited excellent regioselectivity for the synthesis of valuable 3,3',4,4'-tetrasubstituted biphenyls by coupling with each other at the 4-position without the need for additional ligands. Gold catalysts also promoted the oxidative homocoupling of arenes including o-xylene to give symmetrical biaryls with high regioselectivity. X-ray absorption fine structure measurements revealed that the catalytically active species was Au(0) and that the lattice oxygen of Co3 O4 played an important role in the gold-catalyzed oxidative coupling. The results of the kinetic studies were consistent with an electrophilic aromatic substitution pathway. Regioselectivity is not controlled by directing groups or the electronic character of the substituents but by steric hindrance, which suggests that gold nanoparticles not only catalyze the oxidative coupling but also act as bulky ligands to control the regioselectivity.

New Hole Transporting Materials Based on Di- and Tetra-Substituted Biphenyl Derivatives for Organic Light-Emitting Diodes

This study aimed to synthesize novel hole transporting materials (HTMs) with biphenyl derivatives that are di- or tetra-substituted with naphthylphenyl amine groups and/or methoxy groups, and to examine systematically the variations of the properties of the HTMs with the number and location of the substituents. The tetranaphthylphenyl amine-substituted biphenyl-based HTMs T1N and T2N were observed to have better thermal properties than the commercial HTM NPB, with decomposition temperatures above 500 degrees C, and a 10 degrees C higher T(g). In EL devices with ITO/2-TNATA-(60 nm)/HTM(15 nm)/Alq3(70 nm)/LiF(1 nm)/Al structures, the disubstituted biphenyl-based HTMs with an asymmetric molecular structure D1N and D2N were found to have inferior luminescence efficiencies when compared to NPB, which has a symmetric molecular structure. However, M1N, which is substituted with a further two methoxy groups, was found to exhibit excellent luminance and power efficiencies, 4.88 cd/A and 1.36 Im/W respectively at 100 mA/cm2, which are higher by about 147% and 127% respectively than those of NPB (3.30 cd/A and 1.07 Im/W at 100 mA/cm2), due to better charge balance.

The Superbase‐Mediated Pairwise Substitution of the 2,2′‐ and 6,6′‐Positions in a Biphenyl Derivative

AbstractThe superbasic mixture of butyllithium and potassium tert‐butoxide is powerful enough to enable the double proton abstraction from one ortho and one ortho′ position of 4,4′‐di‐tert‐butylbiphenyl. In this way, a series of functionalized derivatives becomes readily accessible, among them 4,4′‐di‐tert‐butylbiphenyldiyl‐2,2′‐dicarboxylic acid (2a) and 4,4′‐di‐tert‐butylbiphenyl‐2,2′‐diol (2d). The latter compound can be subjected again to a superbase‐promoted double metalation, thus giving rise to 2,2′,6,6′‐tetrasubstituted biphenyl derivatives. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Towards peptide versions of Cram's host–guest chemistry: the synthesis of Cα,α-disubstituted glycines with binaphthol-based crowned side-chains

Dietherification of the hydroxy groups of various α,α-disubstituted α-amino acids or their precursors, possessing either an achiral frame derived from α-hydroxymethylserine, or a 2,2′,6,6′-tetrasubstituted biphenyl frame with only an axial chirality, or a frame with α-carbon chirality derived from α-methyl-( L)-DOPA, using ( R)-2,2′-bis-(5-tosyloxy-3-oxa-1-pentyloxy)-1,1′-binaphthyl as alkylating agent, gave a new series of amino acids bearing binaphthol-based crown-ethers, as building blocks for the construction of short-chain peptide helices with topologically well-localized receptors.

Self-assembly of chiral hydrogen-bonded grid layers from terephthalic Siamese twins

2,2′,5,5′-Tetracarboxy- and 2,2′,5,5′-tetracarbamoyl-substituted biphenyls and also the 2,2′,3,3′,6,6′-hexacarboxy-substituted analogue behave as Siamese twins of terephthalic tectons in the single crystal self-assembly, giving rise to chiral 2D grid layers. A comparison has been made with the corresponding 2,2′,6,6′-tetrasubstituted biphenyls which mimic isophthalic twins in their self-assembly.

Tetramethyl biphenyl-3,5,3′,5′-tetracarboxylate benzene sesquisolvate

The title structure, C20H18O8.1.5C(6)H(6), is a tetrasubstituted biphenyl which has a pseudo-inversion centre between the two halves. The benzene solvent molecules lie in special positions, one with twofold rotation symmetry and two with inversion symmetry. The tetramethyl ester molecule is twisted and forms a supramolecular assembly of stacked sheets.

Structure of semirigid polyamides with bulky groups in backbone

The structure of a range of systematically synthesized polyamides, as well as some corresponding component molecular fragments, were studied using wide angle X-ray scattering and computer modeling methods. The molecules all contained tetrasubstituted biphenyls within the amide components, while the aliphatic acid components contained different lengths of the alkyl sequence. A model representing the molecular packing in fiber samples is proposed. It indicates that the polymer backbones are organized in a distorted hexagonal lattice while the intervening pendant side groups still remain randomly packed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 309–319, 1999

Thermoreversible Supramolecular Networks with Polymeric Properties

Hydrogen bonding between carboxylic acids and pyridines can be used as a means of chain extension. However, the reversibility of hydrogen bond formation does not allow the chain-extended structure to be fixed, and a temperature-dependent chain length results. Complexation between a tetrapyridyl species and a diacid is shown to counteract the reversibility of the hydrogen bonding. These complexes form thermoreversible three-dimensional supramolecular networks which have properties typical of low molar mass materials at high temperatures but polymeric properties at low temperatures. The complexes exhibited a glass transition and could form fibers from the melt yet exhibited a low-viscosity isotropic liquid at elevated temperatures. Atypically, a complex incorporating a 2,2',6,6'-tetrasubstituted biphenyl moiety was found to be liquid crystalline.

Rigid rod polyamides based on 2,2′,6,6′‐tetrasubstituted biphenyls: Synthesis, characterization, and structures

AbstractPolyamides based on 4,4′‐diamino‐2,2′,6,6′‐tetrasubstituted biphenyls and phenylterephthalic acid have been synthesized, and the structures and properties of this series of polymer have been studied. It is shown that the polymers have an amorphous structure although some degree of short‐range order is present. This class of polymer, while consisting of comparatively stiff rodlike molecules, demonstrates high solubility and low glass transition temperatures. The behavior is due to the combination of the noncoplanar conformation of the twisted biphenyl and the fact that they have bulky side groups in the 2,2′‐ and 6,6′‐positions that weaken the interchain interactions (like hydrogen bonding and van der Waals forces) and frustrate parallel packing of the polymer chains. © 1994 John Wiley & Sons, Inc.

ChemInform Abstract: Oxazoline‐Mediated Biaryl Coupling Reactions. Stereocontrolled Synthesis of 2,2′,6,6′‐Tetrasubstituted Biphenyls.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Oxazoline-mediated biaryl coupling reactions. Stereocontrolled synthesis of 2,2′,6,6′-tetrasubstituted biphenyls.

High diastereoselectivities (93:7) were observed in the biaryl coupling of 2′,6′-disubstituted aryl Grignard reagents of 1 with aryloxazolines 2. The diastereoselectivities observed in the coupling reaction varied primarily as a function of the chelating properties of the ortho substituents on the aryl Grignard reagent.

Polymenthylenebiphenyl polyanions by metallation—elimination

The 3,3′,5,5′-tetramethylenebiphenyl tetraanion, prepared in good yield by metallation-elimination, gives tetrasubstituted biphenyl derivatives, e.g., with H 2O, D 2O, methyl iodide, and trimethylsilyl chloride. The reaction sequence, starting from alkylated cyclohexanones, provides a general synthetic route to symmetrical polysubstituted biphenyls.

The use of chiral shift reagents in an NMR study of 2,2′,6,6′‐tetrasubstituted biphenyls

AbstractThe determination of the enantiomeric composition of 2,2′,6′6′‐tetrasubstituted biphenyls using 1H NMR spectroscopy, in combination with chiral lanthanide shift reagents, has been studied. In general, the S compounds give largeer induced shifts than the correspondind R isomers when d‐camphor derived shift reagents are used.

Reaction of shielded silicon-containing phenols with peroxides

1. The reaction of shielded silicon-containing phenols (2-trimethylsilyl-4,6-di-tert-butylphenol and 2,6-bis(trimethylsilyl)-4-tert-butylphenol) with benzoyl peroxide in benzene at 80° leads to a dehydro-genation of the phenols with the formation of benzoic acid and phenoxyl radicals. The latter dimerize to give the corresponding disiloxybiphenyls. 2. The indicated phenols under the influence of benzoic acid form 2,4-disubstituted phenols, which react with a new molecule of the starting phenol to give the combined oxidation products, namely 2-hydroxy-2′-trimethylsiloxy-3,3′,5,5′-tetrasubstituted biphenyls.