- Structure-Property Relationships in Unsymmetric Bis(antiaromatics): Who Wins the Battle between Pentalene and Benzocyclobutadiene? ?
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According to the currently accepted structure-property relationships, aceno-pentalenes with an angular shape (fused to the 1,2-bond of the acene) exhibit higher antiaromaticity than those with a linear shape (fused to the 2,3-bond of the acene). To explore and expand the current view, we designed and synthesized molecules where two isomeric, yet, different, 8πantiaromatic subunits, a benzocyclobutadiene (BCB) and a pentalene, are combined into, respectively, an angular and a linear topology via an unsaturated six-membered ring. The antiaromatic character of the molecules is supported experimentally by 1H NMR, UV-vis, and cyclic voltammetry measurements and X-ray crystallography. The experimental results are further confirmed by theoretical studies including the calculation of several aromaticity indices (NICS, ACID, HOMA, FLU, MCI). In the case of the angular molecule, double bond-localization within the connecting six-membered ring resulted in reduced antiaromaticity of both the BCB and pentalene subunits, while the linear structure provided a competitive situation for the two unequal [4n]πsubunits. We found that in the latter case the BCB unit alleviated its unfavorable antiaromaticity more efficiently, leaving the pentalene with strong antiaromaticity. Thus, a reversed structure-antiaromaticity relationship when compared to aceno-pentalenes was achieved.
- El Bakouri, Ouissam,Holczbauer, Tamás,Janáky, Csaba,London, Gábor,Mayer, Péter J.,Ottosson, Henrik,Samu, Gergely F.
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- Coumarin (5,6-Benzo-2-pyrone) Trapping of an HDDA-Benzyne
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Although the parent 2-pyrone is known to react with simple o-benzynes to produce naphthalene derivatives, there appear to be no examples of the successful reaction of coumarin, a benzo-annulated 2-pyrone analogue, with an aryne. We report such a process here using benzynes generated by the hexadehydro-Diels-Alder reaction to produce phenanthrene derivatives (i.e., benzo-annulated naphthalenes). Density functional theory computations were used to help understand the difference in reactivity between 2-pyrone and the slower trapping agent, coumarin. Finally, the reaction of o-benzyne itself [from o-(trimethylsilyl)phenyl triflate and CsF] with coumarin was shown to be viable, although slow.
- Chinta, Bhavani Shankar,Lee, Daniel,Hoye, Thomas R.
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- A convenient synthesis of biphenylene
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An efficient one-pot reaction for the synthesis of biphenylene 1 starting from biphenyl is reported. The final product was prepared from commercially available, cheap materials in moderate yet very competitive yield. Biphenyl was ortho-lithiated to 2,2′-dilithiobiphenyl 2, which was then coupled to biphenylene.
- Schaub, Thomas,Radius, Udo
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- Benzodisilacyclobutadienes: 8π-Electron Systems with an Antiaromatic Silicon Ring
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Benzodisilacyclobutadienes 2 a–c were isolated as blue to green crystalline solids from the reaction of stable disilyne 1 and 1,2-dibromobenzenes in the presence of potassium graphite. In the solid state, substantial bond alternation was observed within the benzene rings of 2 a–c. In hexane, 2 a–c showed remarkable bathochromic shifts of the π→π* (HOMO→LUMO) absorption bands at 625–670 nm. NMR spectra and theoretical calculations indicated that the diamagnetic ring currents of the benzene rings of 2 a–c are considerably reduced by contributions from the antiaromatic 1,2-disilacyclobutadienes. In their entirety, the obtained results indicate that 2 a–c represent 8π-electron systems that contain an antiaromatic 1,2-disilacyclobutadiene.
- Ishida, Shintaro,Misawa, Yoshifumi,Sugawara, Shohei,Iwamoto, Takeaki
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- Formation of biphenylene by elimination of C2 from 9,10-didehydrophenanthrene at 1100°C
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Flash vacuum pyrolysis of phenanthrene-9,10-dicarboxylic anhydride 5 and of 2,2-dimethyl-5-(9'-fluorenylidene)-1,3-dioxan-4,6-dione 8 at 1100°C/0.03-0.04 mm Hg gave pyrolysates which were analysed by 1H NMR spectroscopy and shown to contain phenanthrene 9 as a major constituent and biphenylene 2 as a minor one.
- Brown, Roger F.C.,Coulston, Karen J.,Eastwood, Frank W.
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- An ESR study of the mercuration of the biphenylene radical cation. Evidence for a homolytic mechanism of mercuration
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When a solution of biphenylene in trifluoroacetic acid containing mercury(II) trifluoroacetate is photolysed with ultraviolet light, the ESR spectra show the progressive mercuration of the biphenylene radical cation in the β-position. β-Proton hyperfine coupling β) 76-77 G> appear until tetra-β-mercuration is complete.It is concluded that, apart from the usual electrophilic mechanism, an alternative mechanism for mercuration exists, and that this probably involves collapse of the aromatic radical cation, ArH+., with its counterion, HgX2-.: ArH + HgX2 -> ArH+. + HgX2-. -> HArHgX2 -> ArHgX + HX.
- Courtneidge, John L.,Davies, Alwyn G.,McGuchan, Deborah C.,Yazdi, Safieh N.
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- Could London Dispersion Force Control Regioselective (2 + 2) Cyclodimerizations of Benzynes? YES: Application to the Synthesis of Helical Biphenylenes
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In recent years, London dispersion interactions, which are the attractive component of the van der Waals potential, have been found to play an important role in controlling the regio- and/or stereoselectivity of various reactions. Particularly, the dispersion interactions between substrates and catalysts (or ligands) are dominant in various selective catalyzes. In contrast, repulsive steric interactions, rather than the attractive dispersion interactions, between bulky substituents are predominant in most of the noncatalytic reactions. Herein, we demonstrate the first example of London dispersion-controlled noncatalytic (2 + 2) cyclodimerization of substituted benzynes to selectively afford proximal biphenylenes in high yields and regioselectivities, depending on the extent of dispersion interactions in the substituents. This method can be applied for the synthesis of novel helical biphenylenes, which would be fascinating for chemists as these compounds are potential skeletons for ligands, catalysts, and medicines.
- Akai, Shuji,Aoyama, Hiroshi,Fukumoto, Yutaka,Heguri, Akito,Ikawa, Takashi,Masuda, Yuto,Murakami, Tomonari,Shigeta, Yasuteru,Takagi, Akira,Tokiwa, Hiroaki,Yahata, Kenzo,Yamamoto, Yuta
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p. 10853 - 10859
(2021/07/26)
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- Experimental and theoretical studies on gold(iii) carbonyl complexes: reductive C,H- And C,C bond formation
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The reactivity of cationic (C^C)gold(iii) carbonyl complexes was investigated. While thein situ-formed IPrAu(bph)CO+complex (bph = biphenyl-2,2′-diyl) does not undergo a migratory insertion of CO into the neighboring gold-carbon bond, nucleophiles can attack the coordinated CO moiety intermolecularly. Water as a nucleophile initiates a CO2extrusion combined with a reductive C,H bond formation. The rapid formation of a gold(i) species from an intermediary gold(iii) carbonyl has not been observed before and shows a significant difference in reactivity between (C^C) and (C^N^C)gold(iii) carbonyls. The latter have been reported to form stable gold(iii) hydridesviathe WGS reaction. In the case of methanol acting as a nucleophile attacking the gold(iii) carbonyl, no extrusion of CO2is observed. Instead an intermediary gold(iii) carboxyl complex forms an aryl carboxylateviareductive C-C bond elimination. Experimental and theoretical studies on the mechanism explain the observed selectivities and give new insights into the reactivity of elusive gold(iii) carbonyls.
- Ahrens, Alexander,Dreuw, Andreas,Hashmi, A. S. K.,Hoffmann, Marvin,Karger, Leonhard F. P.,Lustosa, Danilo M.,Rudolph, Matthias
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supporting information
p. 8752 - 8760
(2021/07/02)
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- Metal-Free Selective Borylation of Arenes by a Diazadiborinine via C-H/C-F Bond Activation and Dearomatization
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A newly developed annulated 5-chlorinated 1,3,2,5-diazadiborinine derivative (4) selectively activates a C-H bond of benzene (C6H6) and 1,3-di(trifluoromethyl)benzene, as well as a C-F bond in partially fluorinated arenes, to furnish borylation products under catalyst-, metal-, and irradiation-free conditions. Moreover, 4 readily undergoes a reversible dearomative coupling reaction with polycyclic aromatic hydrocarbons to afford diboration products. The latter represents the first reversible intermolecular dearomative diboration of arenes.
- Su, Yuanting,Huan Do, Dinh Cao,Li, Yongxin,Kinjo, Rei
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supporting information
p. 13729 - 13733
(2019/09/30)
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- How πextension or Structural Bending Alters the Properties of Boron-Doped Phenylene-Containing Oligoacenes
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Linear annulation of two 2,3-biphenylenediyl moieties to a 1,4-dibora-2,5-cyclohexadiene core via its carbon atoms leads to the boron-doped phenylene-containing oligoacene (B-POA) DBI. The optoelectronic properties of DBI are unlike those of related boron-doped polycyclic aromatic hydrocarbons (B-PAHs), such as 6,13-dihydro-6,13-diborapentacene (DBP). Herein we disclose two new B-POAs, which provide insight into fundamental structure-property relationships. The first is a π-extended DBI congener (e-DBI), in which two 2,3-benzo[b]biphenylenediyl moieties are linearly annulated to the central B2C4 ring and behaves partly similar to DBI: it is a strong electron acceptor and has a deep red color. In contrast to the nonluminescent DBI, it shows red fluorescence (quantum yield: 12%), which changes to blue-green upon addition of excess F--ions. In the presence of 0.4 equiv of F-, nearly white emission is observed (CIE1931: (0.3320|0.4056)). If biphenylenediyl moieties are angularly attached to the B2C4 ring via their 1,2-positions, the resulting mixture of "v"- and "z"-shaped B-POA isomers (v/z-DBI) behaves distinctly different from linear DBI: the electrode potentials required for the reversible two-electron reductions of v/z-DBI are significantly more cathodic, and v/z-DBI is an orange rather than red solid and emits green light (quantum yields 65%) upon irradiation.
- Kirschner, Sven,Uecker, Ise,Bolte, Michael,Lerner, Hans-Wolfram,Wagner, Matthias
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supporting information
p. 2818 - 2823
(2019/08/12)
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- Connecting two phenazines with a four-membered ring: The synthesis, properties and applications of cyclobuta[1,2-: B:3,4- b ′]diphenazines
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Herein we report cyclobuta[1,2-b:3,4-b′]diphenazine (CBDP), a new π-electron molecular scaffold containing two phenazine moieties connected by a four-membered ring. With properly positioned silylethynyl substituting groups, CBDP offers a chromophore with
- Yang, Shuaijun,Chu, Ming,Miao, Qian
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supporting information
p. 3651 - 3657
(2018/04/12)
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- Migratory Insertion of Carbenes into Au(III)-C Bonds
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Migratory insertion of carbon-based species into transition-metal-carbon bonds is a mechanistic manifold of vast significance: it underlies the Fischer-Tropsch process, Mizoroki-Heck reaction, Ziegler-Natta and analogous late-transition-metal-catalyzed olefin polymerizations, and a number of carbonylative methods for the synthesis of ketones and esters, among others. Although this type of reactivity is well-precedented for most transition metals, gold constitutes a notable exception, with virtually no well-characterized examples known to date. Yet, the complementary reactivity of gold to numerous other transition metals would offer new synthetic opportunities for migratory insertion of carbon-based species into gold-carbon bonds. Here we report the discovery of well-defined Au(III) complexes that participate in rapid migratory insertion of carbenes derived from silyl- or carbonyl-stabilized diazoalkanes into Au-C bonds at temperatures ≥ -40 °C. Through a combined theoretical and experimental approach, key kinetic, thermodynamic, and structural details of this reaction manifold were elucidated. This study paves the way for homogeneous gold-catalyzed processes incorporating carbene migratory insertion steps.
- Zhukhovitskiy, Aleksandr V.,Kobylianskii, Ilia J.,Wu, Chung-Yeh,Toste, F. Dean
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supporting information
p. 466 - 474
(2018/03/21)
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- Cyclopropyl Group: An Excited-State Aromaticity Indicator?
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The cyclopropyl (cPr) group, which is a well-known probe for detecting radical character at atoms to which it is connected, is tested as an indicator for aromaticity in the first ππ* triplet and singlet excited states (T1 and S1). Baird's rule says that the π-electron counts for aromaticity and antiaromaticity in the T1 and S1 states are opposite to Hückel's rule in the ground state (S0). Our hypothesis is that the cPr group, as a result of Baird's rule, will remain closed when attached to an excited-state aromatic ring, enabling it to be used as an indicator to distinguish excited-state aromatic rings from excited-state antiaromatic and nonaromatic rings. Quantum chemical calculations and photoreactivity experiments support our hypothesis; calculated aromaticity indices reveal that openings of cPr substituents on [4n]annulenes ruin the excited-state aromaticity in energetically unfavorable processes. Yet, polycyclic compounds influenced by excited-state aromaticity (e.g., biphenylene), as well as 4nπ-electron heterocycles with two or more heteroatoms represent limitations.
- Ayub, Rabia,Papadakis, Raffaello,Jorner, Kjell,Zietz, Burkhard,Ottosson, Henrik
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supporting information
p. 13684 - 13695
(2017/09/07)
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- Activity on Leishmania tropica of metal complexes with NNOO tetradentate Schiff base ligand: Kinetic and thermodynamic studies from TG-DTA analysis
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In the search for antileishmanial drug, tetradentate Schiff base ligand 2-{(E)-[(2-{[(Z)-(2-hydroxyphenyl)methylidene]amino}phenyl)imino]methyl}phenol (H2L) was reacted with transition metal ions to yield the complexes of the composition ML [where M = Co (II), Ni (II), Cu (II), & Zn (II)]. The copper based compound 3 (IC50 = 5.857 μM) showed activities even higher than the standard drug. TG and DTA analyses under static air in the temperature range 30-1000 °C were also observed for all the compounds. The TG-DTA analyses and the subsequent themodynamic and kinetic parameters calculated using the TG-DTA curves, have potential relevance for the biological activities. Horowitz-Metzger method was applied for calculating the activation energies and order of pyrolysis. Thermodynamic parameters like ΔS?, ΔH? and ΔG? were subsequently calculated using the corresponding expressions. The order of decreasing thermal stability and decreasing activation energy follow the orders Ni(II) >Co(II) >Zn(II) >Cu(II) and E?Cu>E?Co>E?Ni>E?Zn, respectively.
- Ikram, Muhammad,Rehman, Sadia,Jamal, Qaisar,Shah, Akram
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p. 869 - 878
(2016/01/12)
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- Aryne-Mediated Arylation of the 3-Benzazepine Scaffold: One-Pot Synthesis of 1-Aryl-3-methyl-2,3,4,5-tetrahydro-1 H -3-benzazepines
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The coupling of β-amino carbanions derived from 3-benzA"azeA"pines with in situ generated arynes has been demonstrated as a convenient route for the direct synthesis of a variety of 1-aryl-3-methyl-2,3,4,5-tetrahydro-1H-3-benzazepines, including the biologically active drug molecule SCH 12679.
- Singh, Kamal Nain,Singh, Paramjit,Sharma, Esha,Kaur, Manjot,Deol, Yadwinder Singh
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p. 3212 - 3220
(2015/10/19)
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- Probing mechanisms of aryl-aryl bond cleavages under flash vacuum pyrolysis conditions
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Several biaryls have been subjected to flash vacuum pyrolysis (FVP) at 1100°C and 0.8-0.9hPa. Product compositions are reported for the FVP of 9-phenylanthracene (1), 2-bromobiphenyl (5), biphenyl (8), 1,10- diphenylanthracene (12), 9-(2-naphthyl)anthracene (17), and 9,9′- bianthracenyl (20). The experimental results have been used to evaluate four possible mechanistic pathways for the cleavage of aryl-aryl bonds under these conditions: (1) the 'explosion' of substituted phenyl radicals; (2) hydrogen atom attachment to an ipso-carbon atom of the biaryl followed by C-C bond cleavage; (3) direct homolysis; and (4) loss of a fragment as an aryne. None of these mechanisms by itself successfully accommodates all of the experimental facts. The data suggest that aryl-aryl bond cleavages under FVP conditions involve at least two different mechanistic pathways and that the relative contributions of the competing pathways probably vary from one biaryl to the next.
- Jackson, Edward A.,Xue, Xiang,Cho, Hee Yeon,Scott, Lawrence T.
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p. 1279 - 1287
(2014/11/08)
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- Oxidative addition of carbon-carbon bonds with a redox-active Bis(imino)pyridine iron complex
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Addition of biphenylene to the bis(imino)pyridine iron dinitrogen complexes, (iPrPDI)Fe(N2)2 and [( MePDI)Fe(N2)]2(μ2-N2) (RPDI = 2,6-(2,6-R2-6H3=CMe) 2C5H3N; R = Me, iPr), resulted in oxidative addition of a C- bond at ambient temperature to yield the corresponding iron biphenyl compounds, (RPDI)Fe(biphenyl). The molecular structures of the resulting bis(imino)pyridine iron metallacycles were established by X-ray diffraction and revealed idealized square pyramidal geometries. The electronic structures of the compounds were studied by Moessbauer spectroscopy, NMR spectroscopy, magnetochemistry, and X-ray absorption and X-ray emission spectroscopies. The experimental data, in combination with broken-symmetry density functional theory calculations, established spin crossover (low to intermediate spin) ferric compounds antiferromagnetically coupled to bis(imino)pyridine radical anions. Thus, the overall oxidation reaction involves cooperative electron loss from both the iron center and the redox-active bis(imino)pyridine ligand.
- Darmon, Jonathan M.,Stieber, S. Chantal E.,Sylvester, Kevin T.,Fernandez, Ignacio,Lobkovsky, Emil,Semproni, Scott P.,Bill, Eckhard,Wieghardt, Karl,Debeer, Serena,Chirik, Paul J.
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supporting information
p. 17125 - 17137
(2013/01/15)
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- Reaction of benzyne with formamides and acetylimidazole
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The reaction of DMF with o-trimethylsilylphenyl triflate in the presence of CsF afforded dimethyldiphenylammonium triflate, xanthene, and xanthone in 62%, 16%, and 24% yields, respectively. On the other hand, the reaction of dimethylthioformamide with triflate and CsF resulted in diphenyl sulfide, xanthene, and xanthone in 62%, 10%, and 12% yields, respectively. The reaction of acetylimidazole with benzyne gave 9-N,N-diphenylaminoanthracene in 85% yield.
- Okuma, Kentaro,Nojima, Akiko,Nakamura, Yuki,Matsunaga, Nahoko,Nagahora, Noriyoshi,Shioji, Kosei
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experimental part
p. 328 - 332
(2011/05/14)
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- Pitfalls in the photoelectron spectroscopic investigations of benzyne. photoelectron spectrum of cyclopentadienylideneketene
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The 9.24 eV ionization energy often quoted in photoelectron spectroscopic investigations of benzyne is not due to benzyne 1 but to benzene, C 6H6. The 8.9 eV ionization is not due to benzyne either but to cyclopentadienylideneketene 12 when a 10.2 eV band is also present, or to biphenylene 5 when a 7.6 eV band is simultaneously present. Cyclopentadienylideneketene 12 has been generated by flash vacuum thermolysis of four different precursors, which permit a linking of infrared, mass, and photoelectron spectroscopic observations.
- Chrostowska, Anna,Pfister-Guillouzo, Genevieve,Gracian, Franoise,Wentrup, Curt
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experimental part
p. 1084 - 1090
(2011/04/15)
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- Mass spectrometry of benzyne and cyclopentadienylideneketene
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The formation of cyclopentadienylideneketene 2 and benzyne 1 in flash vacuum thermolysis reactions is investigated by on-line mass spectrometry. Compounds 13, 14, and 15 all afford ketene 2, which decomposes to benzyne and CO in the high-temperature regime. Cyclopentadienylideneketene 2 is stable on the microsecond time-scale of neutralization-reionization experiments. Collisional activation mass spectrometry of m/z 76 from 14, 15, and 5 indicates that the C6H4·+ ions most likely undergo ring opening in the mass spectrometer.
- Monsandl, Thomas,MacFarlane, Graham,Flammang, Robert,Wentrup, Curt
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experimental part
p. 1076 - 1083
(2011/04/15)
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- Three component reaction of arynes with cyclic ethers and active methines: Synthesis of ω-trichloroalkyl phenyl ethers
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Synthesis of ω-chlorinated alkyl phenyl ethers by tandem reaction of arynes with cyclic ethers and active methines was achieved. Reaction of benzenediazonium 2-carboxylate with tetrahydropyran or tetrahydrofuran in refluxing chloroform afforded 6,6,6-trichlorohexyl phenyl ether or 5,5,5-trichloropentyl phenyl ether in 40% and 61% yields, respectively. When dichloroacetonitrile was used as a reactant, 5,5-dichloro-5-cyanopentyl phenyl ether was obtained in 61% yield. While benzenediazonium carboxylate did not react with epoxides, reaction of benzyne derived from 2-(trimethylsilyl)phenyl triflate with epoxides afforded 3,3,3-trichloropropyl phenyl ethers in good yields as isomeric mixtures. The reaction of oxetanes with benzyne was also reported.
- Okuma, Kentaro,Fukuzaki, Yuta,Nojima, Akiko,Sou, Ayumi,Hino, Haruna,Matsunaga, Nahoko,Nagahora, Noriyoshi,Shioji, Kosei,Yokomori, Yoshinobu
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experimental part
p. 1238 - 1247
(2010/12/20)
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- Catalytic flash vacuum pyrolysis (CFVP): A new way to afford 7H-dibenzo[b,d]azepin-7-one
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Catalytic flash vacuum pyrolysis (cfvp) of 2-(1H-1,2,3-benzotriazol-1-yl)-phenylethanone (1) was performed over different mesoporous solids of the MCM-41 type: pure Si-MCM-41, Al-MCM-41 and Ti-MCM-41 with Si/metal ratio equal to 20 and 120. While in the absence of the catalyst (conventional fvp) the thermal reaction afforded 7H-dibenzo[b,d]azepin-7-one (5) as the main product between 400 and 500 °C, in the cfvp systems different products were obtained between 350 and 450 °C depending on the type of catalysts. Al-MCM-41 showed the best catalytic performance with azepinone selectivity of 87% at 450 °C. The mechanisms of formation of these different products as well as the effect of different solids are discussed. Mesoporous materials used in this study have been prepared by direct hydrothermal synthesis. Structural regularity was determined by XRD and highly ordered structures were obtained.
- Moyano, Elizabeth L.,Eimer, Griselda A.,Lucero, Paola L.,Chanquia, Corina M.,Herrero, Eduardo R.,Yranzo, Gloria I.
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scheme or table
p. 98 - 103
(2010/10/02)
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- Initiator system with biphenylene derivates, method of production and use thereof
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The invention relates to an initiator system comprising (a) an iodonium salt, (b) a light sensitizer and (c) an electron donor compound comprising a biphenylene structure, the biphenylene structure comprising at least one but not more than about 4 alkyl groups. The invention also relates to a hardenable composition comprising such an initiator system and the use thereof, as well as to a process for producing the substituted biphenylene compound.
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- Cascade approach to trichloroalkyl phenyl ethers from benzyne, epoxides, and chloroform
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The reaction of o-(trimethylsilyl)phenyl triflate with CsF and propene oxide in the presence of chloroform gave an isomeric mixture of trichloroalkyl phenyl ethers in 72% yield. The reaction of 1,2-epoxy-5-hexene with benzyne afforded 1,2-epoxy6-phenyl-3-
- Okuma, Kentaro,Hino, Haruna,Sou, Ayumi,Nagahora, Noriyoshi,Shioji, Kosei
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body text
p. 1030 - 1031
(2010/06/13)
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- Microwave flash pyrolysis
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(Chemical Equation Presented) In a microwave reactor, graphite heats rapidly to high surface temperatures; applications of graphite thermal "sensitization" have been described previously. We report here that microwave thermal sensitization with graphite, carbon nanotubes, or silicon carbide can be used to carry out reactions more typically accomplished by flash vacuum pyrolysis (FVP) and which usually require temperatures much higher than the nominal limit of a microwave reactor. The graphite-sensitized microwave reaction of azulene in the solid phase at temperatures of 100 to 300°C affords rapid rearrangement to naphthalene, a reaction typically observed by FVP at 700-900°C. Multiwall carbon nanotubes give similar results when used as a thermal sensitizer. Other graphite-sensitized reactions that we have observed include the following: conversion of 2-ethynylbiphenyl to phenanthrene, fragmentation of phthalic anhydride to benzyne, cleavage of iodobenzene to phenyl radical, aryl-aryl bond cleavage, and a variety of cycloaromatizations. An advantage is seen for less volatile substrates. Rearrangement of azulene and generation of benzyne from phthalic anhydride have also been observed on powdered silicon carbide. Because of the high temperature, rapid heating, and frequent ejection of material from the irradiation zone, we refer to this general method as microwave flash pyrolysis (MFP).
- Hee, Yeon Cho,Ajaz, Aida,Himali, Dibya,Waske, Prashant A.,Johnson, Richard P.
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experimental part
p. 4137 - 4142
(2009/09/25)
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- One-pot synthesis of 7H-dibenzo[b,d]azepin-7-one by heterogeneous flash vacuum pyrolysis with MCM-41 catalysts
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Homogeneous and heterogeneous flash vacuum pyrolysis (fvp) reactions of 2-(1H-1,2,3-benzo1riazol-1-yl)phenylethanone (1) are reported. Heterogeneous reactions were carried out with Al-MCM-41 catalysts, mesoporous molecular sieves of the type M41S. In both cases, 7H-dibenzo[b,d]azepin-7-one (4) was the major product; however, in the catalytic reactions, yields and selectivity were very high. A mechanism for this reaction is also discussed.
- Moyano, Elizabeth L.,Lucero, Paola L.,Eimer, Griselda A.,Herrero, Eduardo R.,Yranzo, Gloria I.
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p. 2179 - 2181
(2008/02/03)
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- Reactivity of dehydrometallophthalocyanines and - Porphyrazines
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The zinc dehydrophthalocyanine 2 and zinc dehydrobenzoporhyrazine 8a were generated from the 1N-aminobenzotriazole-annulated zinc phtalocyanine 1 and zinc benzoporhyrazine 8, respectively, by oxidation with Pb(OAc)4 in different solvents, for example, diethyl ether, tetrahydrofuran, acetic acid, and benzene. The reactivity of 2 and 8a was studied in detail. These species not only easily undergo Diels-Alder additions with dienes, but also the used solvents can be added. Among the addition products with solvents ethoxy-, acetoxy-, acetoxybutyloxy-substituted and barrelen-fused phthalocyanines and benzoporpyrazines were isolated. No products resulting from the dimerization of two denydro species were observed either for 2 or 8a. Analysis of the reaction products in comparison with those obtained by oxidation of 1-aminobenzotriazole 15 under similar conditions proves a higher reactivity (electrophilicity) of the dehydro-PcZn 2 and dehydro-PzZn 8a in comparison with unsubstituted benzyne towards the solvents used, such as diethyl ether and benzene.
- Vagin, Sergei I.,Frickenschmidt, Antje,Kammerer, Bernd,Hanack, Michael
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p. 985 - 991
(2007/10/03)
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- Highly brominated biphenylenes as precursors for the convenient synthesis of 5,6,8,10-tetrabromobenzocyclooctene
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An efficient synthesis is described of hexabromides 5 and 6 by photobromination of biphenylene (1). Double dehydrobromination of hexabromides 5 and 6 with t-BuOK affords 5,6,8,10-tetrabromobenzocyclooctene (7) in nearly quantitative yield. The tetrabromide 7 is a valuable precursor for the preparation of functionalised substituted benzocyclooctenes (benzo[8]annulenes).
- Tutar, Ahmet,Cakmak, Osman,Karakas, Mehmet,Onal, Adem,Ide, Semra
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p. 545 - 549
(2007/10/03)
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- A p-benzyne to m-benzyne conversion through a 1,2-shift of a phenyl group. Completion of the benzyne cascade
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Pyrolysis of 1,6-diphenylhexa-1,5-diyne-cis-3-ene at 800-1000 °C leads to a mixture of 1- and 2-phenylbiphenylene, along with triphenylene. Formation of the two biphenylenes is taken as strong evidence of the rearrangement of a p-benzyne into a m-benzyne through a shift of one of the phenyl groups. Copyright
- Polishchuk, Alexei L.,Bartlett, Kevin L.,Friedman, Lee A.,Jones Jr., Maitland
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p. 798 - 806
(2007/10/03)
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- Semivolatile and volatile compounds in combustion of polyethylene
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The evolution of semivolatile and volatile compounds in the combustion of polyethylene (PE) was studied at different operating conditions in a horizontal quartz reactor. Four combustion runs at 500 and 850°C with two different sample mass/air flow ratios and two pyrolytic runs at the same temperatures were carried out. Thermal behavior of different compounds was analyzed and the data obtained were compared with those of literature. It was observed that α,ω-olefins, α-olefins and n-paraffins were formed from the pyrolytic decomposition at low temperatures. On the other hand, oxygenated compounds such as aldehydes were also formed in the presence of oxygen. High yields were obtained of carbon oxides and light hydrocarbons, too. At high temperatures, the formation of polycyclic aromatic hydrocarbons (PAHs) took place. These compounds are harmful and their presence in the combustion processes is related with the evolution of pyrolytic puffs inside the combustion chamber with a poor mixture of semivolatile compounds evolved with oxygen. Altogether, the yields of more than 200 compounds were determined. The collection of the semivolatile compounds was carried out with XAD-2 adsorbent and were analyzed by GC-MS, whereas volatile compounds and gases were collected in a Tedlar bag and analyzed by GC with thermal conductivity and flame ionization detectors.
- Font, Rafael,Aracil, Ignacio,Fullana, Andrés,Conesa, Juan A.
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p. 615 - 627
(2007/10/03)
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- Synthesis of optically active benzocyclobutene and biphenylene based unusual α-amino acid derivatives
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Optically active benzocyclobutene and biphenylene based unusual α-amino acid derivatives have been prepared via a six step sequence using Schoellkopf chiral auxiliary in a very high diastereoselective manner.
- Kotha, Sambasivarao,Halder, Somnath
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p. 863 - 872
(2007/10/03)
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- Synthesis of biphenylenes and tetraphenylenes using copper-catalyzed coupling of arylzinc intermediates
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Biphenylene and some of its 2,3,6,7- and 1,8-substituted derivatives were synthesized using the CuCl2-mediated intramolecular coupling of an organozinc species prepared from 2,2′-dilithiobiaryls with one or two molar equiv. of ZnCl2 or ZnBr2 in THF. Although most of the reactions of 2,2′-dilithiobiaryls with CuCl2 in THF in the absence of ZnCl2 or ZnBr2 led to biphenylenes as a major product, similar reactions of the organozinc species with CuCl2 in THF produced biphenylenes in much better yields, due to smooth transmetallation and reductive elimination reactions. In particular, the copper-mediated cyclization of benzannelated organozinc intermediates, prepared from equimolar proportions of 2,2′-dilithiobiaryls with ZnCl2, proceeded smoothly and selectively to afford the desired biphenylenes in 46-81% yield except for the reaction of the zinc intermediate derived from 4,4′,5,5′-tetramethoxy-2,2′-dilithiobiphenyl with ZnCl2 (1.0 molar equiv.). The reaction of the tetramethoxy-substituted organozinc species with CuCl2 produced 2,3,6,7,10,11,14,15-octamethoxytetraphenylene as a major product in 67% yield.
- Kabir, S.M. Humayun,Hasegawa, Masashi,Kuwatani, Yoshiyuki,Yoshida, Masato,Matsuyama, Haruo,Iyoda, Masahiko
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p. 159 - 165
(2007/10/03)
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- Novel synthesis of biphenylene and its derivatives using intramolecular coupling of zincacyclopentadienes
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Biphenylene and its derivatives were synthesized using the intramolecular coupling of benzoannelated zincacyclopentadiene intermediates prepared from 2,2'-dilithiobiaryls with ZnCl2. The reaction proceeded smoothly and selectively to give the desired biphenylenes in moderate to good yields.
- Iyoda, Masahiko,Kabir, S. M. Humayun,Vorasingha, Anusorn,Kuwatani, Yoshiyuki,Yoshida, Masato
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p. 5393 - 5396
(2007/10/03)
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- Formation of cyclopent[a]indene and acenaphthylene from allyl esters of biphenyl mono- and di-carboxylic acids and from biphenyl dicarboxylic anhydrides on flash vacuum pyrolysis at 1000-1100°C
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Flash vacuum pyrolysis at 1000-1100°C of the allyl esters of the three isomeric biphenylcarboxylic acids, of the allyl esters of the 12 biphenyldicarboxylic acids and of the three biphenyldicarboxylic anhydrides gave pyrolysates which were examined by 1H n.m.r. spectroscopy at temperatures below -50°C. In all cases the spectra showed the presence of cyclopent[a]indene and acenaphthylene together with other products. Possible mechanisms for these ring contraction and cyclization processes are discussed and the results of pyrolyses of [2,3-13C2]biphenyl-2,3-dicarboxylic anhydride, and [3,4-13C2]-and (2-2H1)-biphenyl-3,4-dicarboxylic anhydrides are reported.
- Bapat, Jayant B.,Brown, Roger F.C.,Bulmer, Glenn H.,Childs, Trevor,Coulston, Karen J.,Eastwood, Frank W.,Taylor, Dennis K.
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p. 1159 - 1182
(2007/10/03)
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- Multiple chemically functional end cap monomers
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Thermomechanical and thermo-oxidative stabilities in resin composites across the range of aerospace engineering thermoplastic resins are improved by forming four crosslinks at each addition polymerization site in the backbone of the resin using crosslinking functionalities of the general formula: STR1 β=the residue an organic radical selected from the group consisting of: STR2 R8 =a divalent organic radical; X=halogen; Me=methyl T=allyl or methallyl. G=--CH2 --, --S--, --CO--, --SO--, --O--, --CHR3 --, or --C(R3)2 --; i=1 or 2; R3 =hydrogen, lower alkyl, lower alkoxy, aryl, or aryloxy; and Θ=--C N, --O--C N, --S--C N, or --CR3 =C(R3)2.
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- Intramolecular Trapping of a Ketenimine Carbene Formed on Flash Vacuum Pyrolysis of 3-Phenylimino-3H-indazole and 3-Phenyliminoisobenzofuran-1-one
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Flash vacuum pyrolysis of 3-phenylimino-3H-indazole yielded biphenylene, benzonitrile and, by loss of dinitrogen followed by intramolecular trapping of a ketenimine carbene intermediate, the isomers fluorenimine, phenanthridine and 2-phenylbenzonitrile.Pyrolysis of 3-phenyliminoisobenzofuran-1-one gave the same five products together with N-phenylphthalimide.It is proposed that the same ketenimine carbene intermediate is involved in the two reactions.Pyrolysis of 3-o-tolylimino- and 3-benzylimino-isobenzofuran-1-one led to fragmentation without intramolecular trapping.Pyrolysis of 3-t-butyliminoisobenzofuran-1-one gave o-cyanobenzoic acid.
- Brown, Roger F. C.,Coulston, Karen J.,Eastwood, Frank W.
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- Cyclopentindene (Benzopentalene): Generation by Flash Vacuum Pyrolysis and Subsequent Dimerisation
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Cyclopentindene (benzopentalene, 7) is generated by flash vacuum pyrolysis of 3-phenylphthalic anhydride (6), biphenylene (3) or diphenic anhydride (4).It dimerises readily and adds cyclopentadiene above -70 deg C, but it does not equilibrate at 900 deg C with as-indacene (1).
- Brown, Roger F. C.,Choi, Neil,Coulston, Karen J.,Eastwood, Frank W.,Wiersum, Ulfert E.,Jenneskens, Leonardus W.
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p. 4405 - 4408
(2007/10/02)
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- Synthesis of Benzo-Fused Benzodiazepines Employed as Probes of the Agonist Pharmacophore of Benzodiazepine Receptors
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The synthesis and in vitro evaluation of benzo-fused benzodiazepines 1-6 are described.These "molecular yardsticks" were employed to probe the spatial dimensions of the lipophilic pocket L2 in the benzodiazepine receptor (BzR) cleft and to dete
- Zhang, Weijiang,Koehler, Konrad F.,Harris, Bradford,Skolnick, Phil,Cook, James M.
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p. 745 - 757
(2007/10/02)
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- Formation of polycyclic aromatic compounds upon electric discharges in liquid toluene
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The formation of a great number of polycyclic aromatic compounds up to 604 mass number occurs when electric discharges are made in liquid toluene with one or both electrodes being graphite.
- Beck, Mihaly T.,Dinya, Zoltan,Keki, Sandor
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p. 4919 - 4928
(2007/10/02)
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- Novel poly(arylcyclobutenes)
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The invention is a poly(arylcyclobutene) comprising arylcyclobutene moieties connected by a bridging member, which comprises a polyvalent organic radical which comprises carbonyloxy moieties which are bound to each aryl moiety, and a hydrocarbon poly-yl optionally containing N, O, S or P, wherein each carbonyloxy moiety is bound to such poly-yl, and wherein one or more cyclobutene rings are fused to one of the aryl rings.
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- Benzoxathiete and related structures: experimental and quantum chemical studies
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The products, plausible intermediates, and their mechanisms of formation in the aprotic diazotization of 2-anilines with isoamyl nitrate have been investigated by experimental and quantum chemical methods.Oxidation of 1,2,3-benzthiadiazole with hydrogen peroxide in acetic acid affords 1,2,3-benzthiadiazole-1-oxide, 13.The thermal stability of 13 up to 135 deg C, together with EPR evidence which disfavors an aryldiazenyl radical precursor, discount 13 as an intermediate in the formation of benzoxathiete 14 or its valence tautomer 17 during aprotic diazotization of the sulfinylanilines.Electron paramagnetic resonance evidence in conjunction with spin trapping indicates an intermediate arylaminyl radical.This evidence, taken together with ab initio calculations of optimized geometries energies and energy differences for biradical intermediate 15, favors a mechanism of formation of benzoxathiete 14 via aryldiazoate anhydrite 5 thence to rapid ring closure of carbon-centered radical 8.Further oxidation of 1,2,3-benzthiadiazole-1-oxide, 13, with hydrogen peroxide in methanol - acetic acid affords biphenylene and dibenzo-1,4-oxathiane-S-oxide, 38.Rose bengal sensitized photooxidation of 1,2,3-benzthiadiazole affords 13, biphenylene, and 38.Formation of the latter, in which one of the original S-O bonds has been broken, requires the formation of benzoxathiete-S-oxide, 34, and its rapid valence tautomerism to ketosulfine 36 and (2 + 4) cycloaddition of 36 to the simultaneously generated dehydrobenzene to give 38.Both ring closure of singlet biradical 35 to 34 and valence tautomerism of the latter to 36 are predicted by ab initio calculations to be facile and exothermic.In contrast to the aprotic diazotization of 2-anilines, the reaction of isoamyl nitrite with the corresponding sulfonyl anilines may plausibly follow a mechanism via 1,2,3-benzthiadiazole-1,1-dioxide 33 owing to the thermal instability of the latter and supported by ab initio treatments of the energetics of the processes involved.In addition EPR evidence, in conjunction with spin trapping of carbon centered radicals, support the viability of the pathway via 23, 25, 28, and 16 to biphenylene 20.The ab initio calculations of the energy differences between the reaction intermediates and estimates of the activation energies elucidated several aspects of these novel reaction.
- Naghipur, Ali,Reszka, Krzysztof,Lown, J. William,Sapse, Anne-Marie
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p. 1950 - 1960
(2007/10/02)
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- Benzyne-Oxazole Cycloadducts: Isolation and Retro-Diels-Alder Reactions
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A literature procedure for generating benzyne from 1-aminobenzotriazole and lead tetraacetate was modified by the use of two syringe pumps to effect simultaneous addition through opposing ports of a three-neck flask.Applied to the reaction of benzyne with 4-phenyloxazole at 0 deg C, this modification resulted in essentially quantitative formation of cycloadduct.Retro-Diels-Alder expulsion of benzonitrile with concurrent formation of isobenzofuran occurred when the adduct was heated.The sequence constitutes a useful method of preparation of isobenzofuran, which may be utilized in situ or isolated as a solution for subsequent application.Benzyne cycloadducts were also prepared from 4-(4-nitrophenyl)- and 4-(4-methoxyphenyl)oxazoles, in order to assess the effect of remote substituents on the retro-Diels-Alder reaction.First-order rate constants were determined at three temperatures in the range of 40-70 deg C.The order of reactivity was p-NO2 > p-H > p-OMe; the substituent effects were small, with a factor 4 separating the p-NO2 from p-OMe rate.All three substrates exhibited small ΔS(excit.) values.Expulsion of the nitrile is believed to occur as a concerted reaction with little charge development.The modified benzyne procedure was also applied to 2,5-diphenyloxazole, at 0 and -78 deg C.Oxazole was recovered (59percent and 43percent at the higher and lower temperature, respectively).No bis(benzyne) adduct was formed, showing that 1,3-diphenylisobenzofuran is not generated during the course of the reaction.The 1:1 benzyne-diphenyloxazole cycloadduct is not observed in the crude product of the0 deg C reaction, but an absorption at 6.09 ppm in the NMR spectrum of crude product from the -78 deg C reaction is attributed to this material.The latter crude product on standing at room temperature forms the isobenzofuran.Both reaction mixtures form 1,3-diphenylisobenzofuran by another mechanism involving a second intermediate.This more polar intermediate, which appears to be the major product at 0 deg C, slowly gives 1,3-diphenylisobenzofuran.The overall more efficient cycloaddition at - 78 deg C is attributed to entropy effects, which tend to favor Diels-Alder over other second-order reactions as the temperature is lowered.
- Whitney, Scott E.,Winters, Michael,Rickborn, Bruce
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p. 929 - 935
(2007/10/02)
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- Cyclopentadienylideneethenone: Pyrolytic Generation and Argon Matrix Infrared Spectroscopic Study
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Two previously reported pyrolytic precursors for cyclopentadienylideneethenone (4) and benzyne produced two strong infrared bands attributable to ketene type compounds when their pyrolysates were examined by argon matrix isolation spectroscopy.To determine which band should be assigned to (4), four new precursors for (4) and benzyne and two analogues labelled with 13C at the carbonyl group have been synthesized.Precursors (8) and (14) are respectively a caged system and a bridged system bearing a mixed anhydride with trifluoroacetic acid.Flash vacuum pyrolysis of (8) and (14) at 600-700 deg with trapping at 77 K gave pyrolysates which contaned biphenylene.Pyrolysis of (8) and (14) at 600-700 deg in a stream of argon followed by deposition as an argon matrix at about 10 K showed that both produced a pyrolysate absorbing at 2089 cm-1 assigned to (4).Precursors (24) and (25) and the previously reported (18) and (27) are Meldrum's acid derivatives designed to yield the hypothetical cyclopentadienylide Meldrum's acid (19) by cage fission or retro-Diels-Alder reaction.They all gave their biphenylene on flash vacuum pyrolysis at 600-700 deg and their pyrolysates in argon matrices showed absorption both at 2089 cm-1 due to (4) and at 2225 cm-1 due to an unidentified ketene.The frequency shift resulting from substitution of 13C in the carbonyl group (52 cm-1) is in accordance with the assignment of the 2089 cm-1 band to (4).The pyrolysates from precursors (8a), (14), (18a), (25) and (27) were allowed to react with methanol and the resulting mixtures were hydrogenated.In all cases methyl cyclopentylacetate was obtained.
- Brown, Roger F. C.,Browne, Neil R.,Coulston, Karen J.,Eastwood, Frank W.,Irvine, Margaret J.,et al.
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p. 1321 - 1344
(2007/10/02)
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- Formation of Benzoxathiete under Mild Conditions and Its Valence Tautomerism in Solution to Monothio-o-benzoquinone: An Experimental and Quantum Chemical Study
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Aprotic diazotization of 2-aniline in dimethoxyethane affords products that include biphenylene and dibenzo-1,4-oxathiane.Detection of these products is consistent with the formation of benzoxathiete and the valence tautomerism to monothio-o-benzoquinone with concomitant formation of dehydrobenzene by a competing pathway.The latter was independently trapped with 1,3-diphenylisobenzofuran and with 9,10-dimethylanthracene.The requirement for SO group participation in the formation of benzoxathiete is established by comparison with the behavior of the analogous thioether and sulfone compounds.EPR and spin-trapping experiments confirm the intermediacy of both oxygen- and nitrogen-centered free radicals which is consistent with the homolytic pathways proposed for the diazotization process.Parallel aqueous diazotization of 2-aniline affords vinyl acetate, phenol, and halobenzene consistent with the generation of dehydrobenzene but not benzoxathiete under these conditions.Spin-trapping/EPR studies gave no evidence for free-radical components in the protic diazotization reaction.Ab initio calculations using the 3-21G* and 6-31G* basis sets within the Hartree-Fock approximation, as well as the MP2/3-21G* method, predict an energetically feasible tautomerism of benzoxathiete to monothio-o-benzoquinone.The 3-21G* calculations reveal the presence of a biradical intermediate for this reaction which, as a singlet, features an energy higher than the benzoxathiete by 33 kcal/mol, while as the corresponding triplet it proves to be lower in energy than the benzoxathiete by 2.5 kcal/mol.This process, however, might be symmetry forbidden.By contrast, the symmetry-allowed cycloreversion pathway of benzoxathiete to dehydrobenzene and SO is energetically much less favorable.
- Naghipur, Ali,Reszka, Krzysztof,Sapse, Anne-Marie,Lown, J. William
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p. 258 - 268
(2007/10/02)
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- Scrambling of the Label in Biphenylene Obtained on Pyrolysis of - and -2-(3',3'-Dimethyltriazenyl)benzoic Acid
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Flash vacuum pyrolysis of 2-(3',3'-dimethyltriazenyl)benzoic acid (6) above 350 deg gives biphenylene and N,N-dimethylaniline.The acid (6) was synthesized with 13C2 labels placed as in (13) to generate benzyne.F.v.p. of labelled acid (13) from 400-850 deg gave biphenylene samples which showed 13C spectra consistent with an increasing extent of carbon rearrangement from benzyne to benzyne with increasing temperature.This is in accord with direct rearrangement of benzyne (Scheme 1) but it is probable that more than one mechanism is operating.The labelling evidence suggests that N,N-dimethylaniline is formed by re-addition of dimethylamine to benzyne.
- Brown, Roger F. C.,Coulston, Karen J.,Eastwood, Frank W.,Vogel, Caspar
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p. 1687 - 1696
(2007/10/02)
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- Biphenylene end-capped quinoxaline polymers and their use as insulating coatings for semiconductor devices
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An insulating or masking film for semiconductor devices formed by curing applied coatings of biphenylene end-capped quinoxaline polymers.
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- Observation of 13C Rearrangement in Biphenylene Formed from Benzyne on Pyrolysis of Phthalic Anhydride and Benzocyclobutenedione
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Examination of biphenylene formed by gas phase pyrolysis of doubly labelled benzyne precursors shows that the principal pyrolytic process leads to overall 1,2 --> 1,3 rearrangement of the C6H4 carbon skeleton either in an intermediate C7H4O before decarbonylation or in benzyne itself.A minor process involves an apparent 1,3-hydrogen shift. Ethyne-1,2-diylbistrimethylsilane was acylated with 3-(2,5-dihydro-1,1-dioxothien-2-yl)propanoyl chloride and the resulting ketone was desilylated to yield 5-(2,5-dihydro-1,1-dioxothien-2-yl)pent-1-yn-3-one.Thermal elimination of sulfur dioxide and cyclization followed by dehydrogenation yielded -2,3-dihydro-1H-inden-1-one which was oxidized and dehydrated to give isobenzofuran-1,3-dione.This doubly labelled phthalic anhydride was diluted to approximately 5percent13C2 and the resulting material was converted via benzenediazonium-2-carboxylate into biphenylene at 84 deg, and pyrolysed at 830 deg to yield biphenylene, and a sample diluted to 7.5percent was converted into benzocyclobutenedione which was pyrolysed at 650 deg, 750 deg and 830 deg to yield further samples of biphenylene.The biphenylene samples were examined by mass spectrometry at 20 eV to determine their isotopic composition and by 13C n.m.r. spectroscopy to determine the distribution of labelling.
- Barry, Martin,Brown, Roger F. C.,Eastwood, Frank W.,Gunawardana, Dionne,Vogel, Caspar
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p. 1643 - 1657
(2007/10/02)
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- Benzocyclobutenes. Part 9. Synthesis of Bromo-, Chloro-, and Oxo-derivatives of Benzocyclobutene and Naphthocyclobutene
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Addition of benzyne to 1,1-dichloro- and 1,1,2-trichloro-ethene gave the corresponding di- (61percent) and tri- (18percent) chloro derivatives of benzo-cyclobutene.Similarly 2,3-didehydronaphthalene and 1,1-dichloroethene gave 1,1-dichloronaphthocyclobutene.Some reactions, including reduction, chlorination, bromination, and hydrolysis of these cyclobutenes and of related compounds are described.
- Abou-Teim, Omar,Goodland, Michael C.,McOmie, F. W.
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p. 2659 - 2662
(2007/10/02)
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