- Exceptional aggregation-induced emission from one totally planar molecule
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Planar molecules usually display aggregation-caused quenching (ACQ). Here, it was found that a completely planar organic compound, 5,7,12,14-tetraoxapentacene A-D-A triad with carbon-oxygen bonds, had no fluorescence in high polar solvents but emitted strong light in suspension and in solid state, showed typical AIE effect. One novel AIE mechanism was disclosed by molecular packing in crystal state. In addition, its exceptional AIE effect showed great potential applications in fluorescent thermometer and highly sensitive sensor for selective detection of nitrophenolic compounds. The detection limit for 2,4,6-trinitrophenol was low to 0.168 nM.
- Yuan, Ying-Xue,Wu, Bai-Xing,Xiong, Jia-Bin,Zhang, Hong-Chao,Hu, Ming,Zheng, Yan-Song
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- Conjugated polymers with large effective stokes shift: Benzobisdioxole- based poly(phenylene ethynylene)s
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Phenyleneethynylene-based conjugated copolymers using benzo[1,2-d:4,5- d′]bis[1,3]dioxole (BDO) in the repeating unit are reported. The electronic structure of the BDO unit imparts a localized HOMO topology while the LUMO is delocalized over the polymer backbone, so that the lowest optical absorption band of the polymer has considerable intramolecular charge transfer character. This contrasts with published donor-acceptor polymers with localized LUMO and delocalized HOMO. The very large Stokes shifts of the monomers, which are due to the small oscillator strength of the lowest optical transition, are largely retained in the polymers as a result of covalently constrained dihedral angles in the substituents (not the backbone), as predicted/explained by calculations.
- Dutta, Tanmoy,Woody, Kathy B.,Parkin, Sean R.,Watson, Mark D.,Gierschner, Johannes
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- 1,2,4,5-Bis-(1,4,7,10,13,16-Hexaoxahexadecamethylene)Benzene: Benzo-Bis-(18-Crown-6)
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1,2,4,5-Bis-(1,4,7,10,13,16-hexaoxahexadecamethylene)benzene (1) is prepared in an one-pot synthesis from 2,5-dihydroxy-1,4-benzoquinone (4) and 1,14-dibromo-3,6,9,12-tetraoxatetradecane (3) in 35percent yield.A study of its host-guest 1:1 and 1:2 alkali metal cation complexation reveals that the cations only interact with the aliphatic oxygen lone pairs, hence, leaving the ?-electron system intact.
- Schlotter, Jacobus J. H.,Mertens, Ingrid J. A.,Wageningen, Andre M. A. van,Mulders, Frederik P. J.,Zwikker, Jan W.,et al.
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- Convenient syntheses, spectroscopic and structural characterisation of bi-functional boranes
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The first examples of bi-functional borane derivatives based around a 1,2,4,5-tetrasubstituted benzene framework are reported. Synthesis of ClBO2C6H2O2BCl (4) is accomplished in three steps (69% overall yield) through the intermediacy of the trimethylsilyl derivative 1,2,4,5-(Me3SiO)4C6H2 (3). The bis(borane) species HBO2C6X2O2BH (X=H, 7; X=Cl, 8) on the other hand, can be synthesised in a single step from substituted para-quinone precursors. Crystal structures are reported for compounds 3 and 4.
- Aldridge,Calder,Cunningham,Malik,Steed
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- Fabrication of soft submicrospheres by sequential boronate esterification and their dynamic behavior
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Pyridine-assisted sequential boronate esterification of benzene- 1,4-diboronic acid and 1,2,4,5-tetrahydroxybenzene has induced hierarchical molecular self-assembly, and in turn producing well-defined submicrospheres. Spectroscopic analyses such as FE-SEM, TEM, DLS, NMR, XRD, and IR absorption spectroscopy indicates that the particles are composed of lamellar structures of sp2-hybridized trigonal planar poly(dioxaborole). The spontaneous self-organization is ascribable to reactive layerby- layer assembly through sequential boronate esterification of the diboronic acid and the tetrahydroxybenzene whereby initially formed oligo(dioxaborole) may provide a platform for further reactions, thus resulting in the production of submicrospheres. It is interesting to note that the dynamic covalent functionality as a result of the dioxaborole linkage induced a stimuli-responsive change in morphology by not only a pH switch but also the exchange reaction with pentaerythritol. Further, a selective saccharide-induced change in the submicrosphere morphology was observed through a simple exchange reaction of dynamic covalent boronate esters with saccharides in THF; the selective change in morphology is visually detected through the color change in the solution. These findings can provide a useful insight into the design of stimuli-responsive hierarchical architectures based on boron-containing dynamic covalent bond.
- Nishiyabu, Ryuhei,Teraoka, Shiori,Matsushima, Yusuke,Kubo, Yuji
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- DBD dyes as fluorescence lifetime probes to study conformational changes in proteins
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Previously, [1,3]dioxolo[4,5-f][1,3]benzodioxole (DBD)-based fluorophores used as highly sensitive fluorescence lifetime probes reporting on their microenvironmental polarity have been described. Now, a new generation of DBD dyes has been developed. Although they are still sensitive to polarity, in contrast to the former DBD dyes, they have extraordinary spectroscopic properties even in aqueous surroundings. They are characterized by long fluorescence lifetimes (10-20 ns), large Stokes shifts (≈100 nm), high photostabilities, and high quantum yields (>0.56). Here, the spectroscopic properties and synthesis of functionalized derivatives for labeling biological targets are described. Furthermore, thio-reactive maleimido derivatives of both DBD generations show strong intramolecular fluorescence quenching. This mechanism has been investigated and is found to undergo a photoelectron transfer (PET) process. After reaction with a thiol group, this fluorescence quenching is prevented, indicating successful bonding. Being sensitive to their environmental polarity, these compounds have been used as powerful fluorescence lifetime probes for the investigation of conformational changes in the maltose ATP-binding cassette transporter through fluorescence lifetime spectroscopy. The differing tendencies of the fluorescence lifetime change for both DBD dye generations promote their combination as a powerful toolkit for studying microenvironments in proteins. Polarity probes: New fluorescent dyes based on the [1,3]dioxolo[4,5-f ][1,3]benzodioxole (DBD) skeleton were developed, with fluorescence lifetimes that exhibit a pronounced sensitivity to the polarity of the microenvironment. Several biocompatible derivatives were prepared, and their application was demonstrated with two biochemical examples (see figure; MBP=maltose binding protein).
- Wawrzinek, Robert,Ziomkowska, Joanna,Heuveling, Johanna,Mertens, Monique,Herrmann, Andreas,Schneider, Erwin,Wessig, Pablo
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- [M2(μ-OH)2(DHBQ)3] (M = Zr, Hf) - Two New Isostructural Coordination Polymers based on the Unique M2O14 Inorganic Building Unit and 2,5-Dioxido-p-benzoquinone as Linker Molecule
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Two new isostructural porous coordination polymers (CPs) were obtained under solvothermal reaction conditions using 2,5-dihydroxy-p-benzoquinone (H2DHBQ) or 1,2,4,5-tetrahydroxybenzene (H4THB) as linker molecule and Zr4+ or Hf4+ salts. Highly crystalline compounds with composition [M2(μ-OH)2(DHBQ)3]·xH2O (M = Zr4+ or Hf4+, x = 0–3.6/3.3) were found in a wide temperature range (120–200 °C) and a reaction time of 70 h. The crystal structures were determined ab initio from powder X-ray diffraction data and the oxidation state of the linker was confirmed spectroscopically. The dinuclear inorganic building unit M2O14 is new for Zr- and Hf-CPs. For both compounds a full characterization was carried out, i.e. crystal structure determination, spectroscopic measurements, elemental- and thermogravimetric analyses. [M2(OH)2(DHBQ)3] (M = Zr4+ or Hf4+) is stable up to 250 and 220 °C, respectively. Water sorption measurements proofed an uptake of 3.6 mol H2O per mol and 3.3 mol H2O per mol, respectively.
- Poschmann, Mirjam P. M.,Reinsch, Helge,Stock, Norbert
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- An indirect generation of 1D MII-2,5-dihydroxybenzoquinone coordination polymers, their structural rearrangements and generation of materials with a high affinity for H2, CO2 and CH4
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A series of solid-state structural transformations are found to accompany desolvation of relatively simple coordination polymers to yield materials that exhibit unexpected gas sorbing properties. Reaction of 1,2,4,5-tetrahydroxybenzene with MII salts (M = Mg, or Zn) in an alcohol/water solution in the presence of air affords cis-MII(C6H2O4-II)(H2O)2·2H2O·xROH, (M = Mg, or Zn), crankshaft-like chains in which the absolute configurations of the chiral metal centres follow the pattern ?Δ Δ Λ Λ Δ Δ Λ Λ?, and are hydrogen bonded together to generate spacious channels. When crystals of the crankshaft chain are air dried the crystals undergo a single crystal-to-powder rearrangement to form linear trans-MII(C6H2O4-II)(H2O)2 chains. Further dehydration yields microporous solids that reversibly sorb H2, CH4 and CO2 with high sorption enthalpies.
- Abrahams, Brendan F.,Dharma, A. David,Dyett, Brendan,Hudson, Timothy A.,Maynard-Casely, Helen,Kingsbury, Christopher J.,McCormick, Laura J.,Robson, Richard,Sutton, Ashley L.,White, Keith F.
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- Adsorption and dehydrogenation of tetrahydroxybenzene on Cu(111)
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Adsorption of tetrahydroxybenzene (THB) on Cu(111) and Au(111) surfaces is studied using a combination of STM, XPS, and DFT. THB is deposited intact, but on Cu(111) it undergoes gradual dehydrogenation of the hydroxyl groups as a function of substrate temperature, yielding a pure dihydroxy-benzoquinone phase at 370 K. Subtle changes to the adsorption structure upon dehydrogenation are explained from differences in molecule-surface bonding.
- Bebensee, Fabian,Svane, Katrine,Bombis, Christian,Masini, Federico,Klyatskaya, Svetlana,Besenbacher, Flemming,Ruben, Mario,Hammer, Bjork,Linderoth, Trolle
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- Synthesis of Boroxine and Dioxaborole Covalent Organic Frameworks via Transesterification and Metathesis of Pinacol Boronates
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Boroxine and dioxaborole are the first and some of the most studied synthons of covalent organic frameworks (COFs). Despite their wide application in the design of functional COFs over the last 15 years, their synthesis still relies on the original Yaghi's condensation of boronic acids (with itself or with polyfunctional catechols), some of which are difficult to prepare, poorly soluble, or unstable in the presence of water. Here, we propose a new synthetic approach to boroxine COFs (on the basis of the transesterification of pinacol aryl boronates (aryl-Bpins) with methyl boronic acid (MBA) and dioxaborole COFs (through the metathesis of pinacol boronates with MBA-protected catechols). The aryl-Bpin and MBA-protected catechols are easy to purify, highly soluble, and bench-stable. Furthermore, the kinetic analysis of the two model reactions reveals high reversibility (Keq ～1) and facile control over the equilibrium. Unlike the conventional condensation, which forms water as a byproduct, the byproduct of the metathesis (MBA pinacolate) allows for easy kinetic measurements of the COF formation by conventional 1H NMR. We show the generality of this approach by the synthesis of seven known boroxine/dioxaborole COFs whose crystallinity is better or equal to those reported by conventional condensation. We also apply metathesis polymerization to obtain two new COFs, Py4THB and B2HHTP, whose synthesis was previously precluded by the insolubility and hydrolytic instability, respectively, of the boronic acid precursors.
- Hamzehpoor, Ehsan,Jonderian, Antranik,McCalla, Eric,Perepichka, Dmitrii F.
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supporting information
p. 13274 - 13280
(2021/09/07)
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- Poly(dihydroxybenzoquinone): Its high-density and robust charge storage capability in rechargeable acidic polymer-air batteries
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A rechargeable acidic polymer-air battery was firstly fabricated with poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (PDBM) as the anode, the conventional Pt/C cathode catalyst, and acidic aqueous electrolyte (pH 1). This battery yielded a high discharging capacity of 349 mA h gpolymer-1 with a long-lifetime of >500 cycles and high rate capabilities (up to 10C).
- Furukawa, Shuhei,Murao, Saki,Nishide, Hiroyuki,Oka, Kouki,Oka, Tatsuya,Oyaizu, Kenichi
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supporting information
p. 4055 - 4058
(2020/04/20)
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- New tetralactam hosts for squaraine dyes
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The photophysical properties of a deep-red fluorescent squaraine dye can be improved by encapsulating it within a tetralactam macrocycle. Three new tetralactams are described with different substituents (methyl, methoxy, methylenedioxy) on the macrocycle aromatic sidewalls. The capability of each tetralactam to encapsulate a squaraine dye in chloroform solution was determined experimentally using absorption, fluorescence, and NMR spectroscopy. Two of the tetralactams were found to thread a squaraine dye with association constants on the order of 106 M-1, while a third macrocycle exhibited no squaraine affinity. An X-ray crystal structure of the third tetralactam showed that the substituents sterically blocked squaraine association. Of the two tetralactams that encapsulate a squaraine, one induces an increase in squaraine fluorescence quantum yield, while the other quenches the squaraine fluorescence. The results suggest that these new squaraine binding systems will be useful for biological imaging and diagnostics applications.
- Dempsey, Janel M.,Zhang, Qi-Wei,Oliver, Allen G.,Smith, Bradley D.
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p. 8976 - 8983
(2018/12/10)
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- Reactivity of iPrPCPIrH4 with para-benzoquinones
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In the interest of investigating new hydrogen acceptors for pincer–iridium catalyzed dehydrogenations with the ability to be catalytically recycled, a series of para-benzoquinones have been reacted with iPrPCPIrH4 in various solvents and conditions. Preliminary results indicate that a wide range of quinones are capable of dehydrogenating iPrPCPIrH4, and that several turn-overs in alcohol dehydrogenation by iPrPCPIr are possible at room temperature using benzoquinone acceptors. However, strong acceptor–catalyst interactions are inhibitory toward catalysis when the acceptor is used in excess. A new class of (bis)-η2 pi-adducts, formed between iPrPCPIr and benzoquinones, nicknamed “barber-chairs”, has been identified and 3 examples have been characterized.
- Wilklow-Marnell, Miles,Brennessel, William W.,Jones, William D.
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p. 209 - 214
(2017/11/24)
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- Highly emissive covalent organic frameworks
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Highly luminescent covalent organic frameworks (COFs) are rarely achieved because of the aggregation-caused quenching (ACQ) of stacked layers. Here, we report a general strategy to design highly emissive COFs by introducing an aggregation-induced emission (AIE) mechanism. The integration of AIE-active units into the polygon vertices yields crystalline porous COFs with periodic stacked columnar AIE arrays. These columnar AIE arrays dominate the luminescence of the COFs, achieve exceptional quantum yield via a synergistic structural locking effect of intralayer covalent bonding and interlayer noncovalent interactions and serve as a highly sensitive sensor to report ammonia down to sub ppm level. Our strategy breaks through the ACQ-based mechanistic limitations of COFs and opens a way to explore highly emissive COF materials.
- Dalapati, Sasanka,Jin, Enquan,Addicoat, Matthew,Heine, Thomas,Jiang, Donglin
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supporting information
p. 5797 - 5800
(2016/06/09)
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- The benzoquinone derivatives and their use
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The invention provides a p-benzoquinone derivative and an application thereof. The p-benzoquinone derivative has the inhibitory activity on a plasminogen activator inhibitor-1 (PAI-1); on cellular level, the compound can inhibit the transfer ability of HepG2 liver cancer cells; and in-vitro experiments show that the compound has an inhibition effect on formation of fibrin clots. The p-benzoquinone derivative can be used as a medicine for treating tumors and thrombotic diseases.
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Paragraph 0061;0062
(2016/11/17)
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- Tetramethoxybenzene is a good building block for molecular wires: Insights from photoinduced electron transfer
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Two donor bridge-acceptor molecules with terminal triarylamine and Ru(bpy)32+ (bpy = 2,2′-bipyridine) redox partners were synthesized and investigated by cyclic voltammetry, optical absorption, luminescence, and transient absorption spectroscopy. The two dyads differ only by the central bridging unit, which was tetramethoxybenzene (tmb) in one case and unsubstituted phenylene (ph) in the other case. Photoirradiation of the Ru(bpy)32+ complex of the two dyads triggers intramolecular electron transfer from the triarylamine to the 3MLCT-excited metal complex, and this process occurs with time constants of 1.5 and 6.8 ns for the tmb- and ph-bridged dyads, respectively. Thermal electron transfer in the reverse direction then leads to disappearance of the photoproduct with a time constant of 10 ns in both dyads. The faster rate of photoinduced charge transfer in the tmb-bridged dyad can be understood in the framework of a hole-tunneling model in which the electron-rich tmb bridge imposes a more shallow barrier than the less electron-rich ph spacer. Until now tmb-based molecular wires have received very little attention, and alkoxy substituents have been mostly used for improving the solubility of oligo-p-phenylene vinylene (OPV) and oligo-p-phenylene ethynylene (OPE) wires. Our study illustrates how four alkoxy-substituents on a phenylene backbone can have a significant influence on the charge-transfer properties of a molecular wire, and this is relevant in the greater context of a future molecular electronics technology.
- Heinz, Luisa G.,Yushchenko, Oleksandr,Neuburger, Markus,Vauthey, Eric,Wenger, Oliver S.
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p. 5676 - 5684
(2015/06/16)
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- Design, synthesis, and SAR of embelin analogues as the inhibitors of PAI-1 (plasminogen activator inhibitor-1)
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The natural product embelin was found to have PAI-1 inhibitory activity with the IC50 value of 4.94 μM. Based on the structure of embelin, a series of analogues were designed, synthesized, and evaluated for their ability to inhibit PAI-1. The SAR study on these compounds disclosed that the inhibitory potency largely depended on the hydroxyl groups at C2 and C5, and the length of the alkyl chains at C3 and C6. Compound 11 displayed the best PAI-1 inhibitory potency with the IC50 value of 0.18 μM.
- Chen, Fanglei,Zhang, Guiping,Hong, Zebin,Lin, Zhonghui,Lei, Min,Huang, Mingdong,Hu, Lihong
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supporting information
p. 2379 - 2382
(2014/05/20)
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- Discovery and biological evaluation of novel 1,4-benzoquinone and related resorcinol derivatives that inhibit 5-lipoxygenase
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5-Lipoxygenase (5-LO), an enzyme that catalyzes the initial steps in the biosynthesis of pro-inflammatory leukotrienes, is an attractive drug target for the pharmacotherapy of inflammatory and allergic diseases. Here, we present the discovery and biological evaluation of novel series of 1,4-benzoquinones and respective resorcinol derivatives that efficiently inhibit human 5-LO, with little effects on other human lipoxygenases. SAR analysis revealed that the potency of the compounds strongly depends on structural features of the lipophilic residues, where bulky naphthyl or dibenzofuran moieties favor 5-LO inhibition. Among the 1,4-benzoquinones, compound Ig 5-[(2-naphthyl)methyl]-2- hydroxy-2,5-cyclohexadiene-1,4-dione potently blocked 5-LO activity in cell-free assays with IC50 = 0.78 μM, and suppressed 5-LO product synthesis in polymorphonuclear leukocytes with IC50 = 2.3 mM. Molecular docking studies suggest a concrete binding site for Ig in 5-LO where select π-π interactions along with hydrogen bond interactions accomplish binding to the active site of the enzyme. Together, our study reveals novel valuable 5-LO inhibitors with potential for further preclinical assessment as anti-inflammatory compounds.
- Filosa, Rosanna,Peduto, Antonella,Aparoy, Polamarasetty,Schaible, Anja M.,Luderer, Susann,Krauth, Verena,Petronzi, Carmen,Massa, Antonio,De Rosa, Mario,Reddanna, Pallu,Werz, Oliver
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supporting information
p. 269 - 279
(2013/10/01)
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- Synthesis of polyhydroxylated flavonoids bearing a lipophilic decyl tail as potential therapeutic antioxidants
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Antioxidants have potential for the treatment of stroke and neurodegeneration, and chimeric compounds that combine a flavon-3-ol head group related to myricetin and a lipophilic decyl tail are known to protect membranes from oxidative damage at least as well as vitamin E. New flavon-3-ols that are highly hydroxylated in the B ring in ways not found in natural flavon-3-ols and bearing a lipophilic decyl tail have been prepared from trimethoxy-and tetramethoxybenzoic acids accessed by lithiation-carboxylation reactions. Direct enolate acylation was preferred over Baker-Venkataraman rearrangement when there were methoxy groups at both the 2-and the 6-position of the benzoic acid derivatives.
- Caldwell, Stuart T.,McPhail, Donald B.,Duthie, Garry G.,Hartley, Richard C.
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scheme or table
p. 23 - 33
(2012/03/07)
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- Nanoscale molecular rods with a new building block for solubility enhancement
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(Chemical Equation Presented) A new building block bearing a [1,3]dioxolo[4,5-f][1,3]benzodioxole core was developed to enhance the solubility of molecular rods by lateral alkyl chains. On incorporation in molecular rods with oligospiroketal structure, the straight geometry is retained, which was concluded from the X-ray crystal structure analysis of one of the rods. The determination of the solubility of a collection of rods bearing this building block revealed that already a butyl group efficiently hinders the aggregation of the rods and consequently causes a considerable enhancement of the solubility. Piperidine rings are located at the ends of the rods, which offer the opportunity for versatile functionalization. Thus, an N,N′-bis(azidoacetyl)-functionalized rod was prepared, which could serve as rigid linkage, initiated by a "Click" reaction.
- Wessig, Pablo,Moellnitz, Kristian
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p. 4452 - 4457
(2008/09/21)
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- Tetrahydroxybenzene tetraester derivative and polymer thereof
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The invention includes compounds represented by Formula (1): wherein R1 is an alkyl having 1 to 20 carbon atoms; A1 and A2 are a 1,4-cyclohexylene or 1,4-phenylene; X is a single bond, —C≡C—, —COO—, —OCO—, —CH═CH—COO— or —OCO—CH═CH—; P is an alkylene having 1 to 20 carbon atoms; and p and q are 0, 1 or 2.
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- Reactions of 1,4-benzoquinones with s2 reducing centers
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Aqueous solutions of Sn(II) and Ge(II) (in chloride media) and In(I) (in perchlorate media) react quantitatively with 1,4-benzoquinone and its 2,5-(OH)2 and 2,5-Cl2-3,6-(OH)2 derivatives, reducing the oxo-functions to 1,4-(OH)2. For Sn(II) and Ge(II), reaction is accelerated by incorporation of 2,5-(OH)2 substituents and by chloroanation of the s2 center. The most reactive reducing Sn(II) species are SnCl3- for benzoquinone and dihydroxyquinone but SnCl2(aq)x for the dichloroquinone. Reductions by Ge(II) proceed mainly through a species (probably GeCl 42-) having one more chloride than the predominant form. The activated complex for the (OH)2bzq-Ge(II) reaction features two germanium centers, only one of which is involved in the reduction act. Reductions of these quinones by In(I) proceed 102-103 times as rapidly as those by Sn(II) and Ge(II) and are not accelerated by hydroxylation of the quinone ring. The Royal Society of Chemistry 2003.
- Yang, Zhiyong,Gould, Edwin S.
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p. 2219 - 2223
(2007/10/03)
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- General synthesis of persistent trityl radicals for EPR imaging of biological systems.
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In this paper we describe the syntheses of the tetraoxygenated triarylmethyl (trityl) radical 14 and the tetrathiatriarylmethyl (trityl) radicals 15 and 16. The syntheses include new and improved preparations of the key intermediate compounds 1 and 2. The new route to compound 2 is noteworthy for its efficiency and its avoidance of the highly toxic compound phosgene as well as the isolation of the air-sensitive 1,2,4,5-benzenetetrathiol.
- Reddy, T Jagadeeswar,Iwama, Tetsuo,Halpern, Howard J,Rawal, Viresh H
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p. 4635 - 4639
(2007/10/03)
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- Triarylmethyl radicals and the use of inert carbon free radicals in MRI
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A radical compound of formula Ia wherein: each Ar12, which may be the same or different, represents a 6-membered carbocyclic, at least one group Ar12 being a group Ar1 ; each group Ar1 represents a 6-membered ring optionally substituted at the or any ortho carbon by a group R1, R2, R3 or R4, at the or any meta carbon by a group R2 or R3, and at any para carbon by a group R1, R2, R3 or R4, with the proviso that no more than two ring carbons are unsubstituted; each of R1, R2, R3 or R4, which may be the same or different, independently represents a group of formula --M, --XM, --XAr2 or --Ar2 ; M represents a water solubilizing group, each group X, which may be the same or different, represents an oxygen or sulphur atom or a NH or CH2 group.
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- 2,3,5,6-Tetraalkoxy-1,4-benzoquinones and structurally related tetraalkoxy benzene derivatives: Synthesis, properties and solid state packing motifs
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A general synthesis of 2,3,5,6-tetraalkoxy-1,4-benzoquinones 1 from 1,2,4,5-tetraalkoxybenzenes 3 is reported. IR analysis (1a-e), the single crystal X-ray analysis of 2,3,5,6-tetramethoxy-1,4-benzoquinone 1a and semi-empirical calculations (AM1, 1a) show that the 1,4-benzoquinone skeleton possesses a merocyanine-type distortion. The solid state packing motifs of 1 are markedly affected by alkoxy chain length. For 1a, weak C-H ... O interactions and reduction of unfavourable dipole-dipole interactions are important for intermolecular organization, whereas for 2,3,5,6-tetradecyloxy-1, 4-benzoquinone [1e, wide angle X-ray diffraction (WAXD)] the close packing principle of the alkyl chains dominates. In both cases the results show that interplanar overlap is improved with respect to 1,4-benzoquinone 8. To deepen our insight into the effect of alkoxy chain length on solid state packing motifs, single crystal X-ray structures of methoxy and decyloxy derivatives of the structurally related compounds 1,4-diacetoxy-2,3,5,6-tetraalkoxybenzenes 2a and e, and 1,2,4,5-tetraalkoxybenzenes 3a and e were analysed. Compounds 1e, 2e and 3e, bearing decyloxy chains, possess board-like molecular structures which stack parallel along the a-axis as a result of alkyl chain interactions.
- Keegstra, Erik M. D.,Huisman, Bart-Hendrik,Paardekooper, Elizabeth M.,Hoogesteger, Frans J.,Zwikker, Jan W.,Jenneskens, Leonardus W.,Kooijman, Huub,Schouten, Arie,Veldman, Nora,Spek, Anthony L.
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p. 229 - 240
(2007/10/03)
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- Oxidative Cyclization of Unsaturated Aminoquinones. Synthesis of Quinolinoquinones. Palladium-Catalyzed Synthesis of Pyrroloindoloquinones
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2-Allyl-3,6-diamino-5-methyl-1,4-benzoquinone (1) underwent a facile oxidative cyclization to produce quinolinoquinone 3 in the presence of a variety of oxidizing agents, including palladium(II) salts.Chloranil was the most efficient oxidizing agent and produced 3 in high yield.Under hydrolysis conditions, (hydroxyethyl)benzobis(oxazole) 4 underwent a retroaldol reaction, followed by an aldehyde amine condensation and an electrocyclic cyclization to form quinolinoquinones.In contrast, 2-allyl-3,6-bis(benzylamino)-5-methyl-1,4-benzoquinone (13) underwent smooth, palladium(II)-catalyzed cyclization to form the corresponding indoloquinone.The corresponding bis(allylamino)benzoquinone 17 underwent a similar cyclization, followed by an olefin insertion reaction to form pyrroloindoloquinones 20 and 21.
- Weider, Paul R.,Hegedus, Louis S.,Asada, Hideki,D'Andreq, Stanley V.
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p. 4276 - 4281
(2007/10/02)
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