- 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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- A three-step process to facilitate the annulation of polycyclic aromatic hydrocarbons
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A new efficient three-step process to annulate polycyclic aromatic hydrocarbons (PAHs) has been developed, providing access to PAHs with saturated rings that under current chemical methods would be difficult to produce in an efficient manner. This method relies on a palladium-catalyzed cross-coupling reaction of various brominated PAHs with cyclohexanone to yield α-arylated ketones, which are converted to regiospecific vinyl triflates and cyclized by a palladium-catalyzed intramolecular arene-vinyl triflate coupling to produce PAHs with incorporated saturated rings or "tetrahydroindeno-annulated" PAHs.
- Martin, Sara E.,Streeter, Matthew D.,Jones, Laurel L.,Klepfer, Matthew S.,Atmatzidis, Kyriakos,Wille, Kristen D.,Harrison, Sean A.,Hoegg, Edward D.,Sheridan, Heather M.,Kramer, Stephanie,Parrish, Damon A.,Amick, Aaron W.
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p. 8324 - 8330
(2015/03/18)
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- A new Suzuki-Heck-type coupling cascade: Indeno[1,2,3]-annelation of polycyclic aromatic hydrocarbons
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Under palladium catalysis, o-bromobenzeneboronic acid can be coupled with 1-bromonaphthalene (6) and with oligocyclic bromoarenes to furnish indeno-annelated polycyclic aromatic hydrocarbons 1-4 and 25 in a single operation in moderate to good yields (27-87%). Alternatively, o-dibromoarenes and 1,2-dibromocycloalkenes can be cross-coupled with 1-naphthaleneboronic acid under the same conditions to yield analogous products (6-87%), and indenocorannulene (19) can be prepared likewise in a single step from pinacol corannuleneboronate (18) (40%).
- Wegner, Hermann A.,Scott, Lawrence T.,De Meijere, Armin
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p. 883 - 887
(2007/10/03)
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- Synthesis of benz[1,2-a]aceanthrylene from triptycene via flash vacuum thermolysis
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Benz[1,2-a]aceanthrylene is prepared from triptycene in 60 % yield by flash vacuum thermolysis at 875°C.
- Plummer, Ben,Guterriez, Steve,Navikov, Alexei,Goodman, Dawn
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p. 3213 - 3217
(2007/10/03)
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- Thermolysis and photolysis of 1-substituted triptycenes. Divergent fragmentation pathways of the triptycyl skeleton
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While thermolysis of 1-benzyltriptycene 1a in the gas phase at 600°C/10-4 mmHg did not result in any appreciable decomposition, similar pyrolysis of compounds 1 bearing various substituents (X) at the benzyl methylene (1b-d) underwent smooth decomposition to give 8-benzylbenz[a]aceanthrylene 2. The reaction is explained in terms of homolysis of the C-X bond followed by triptycyl ring cleavage in the resulting benzyl radical 7. Generation of radical 7 in solution, however, did not result in a similar ring-opening reaction. Irradiation of compounds 1, on the other hand, afforded norcaradienes 3 almost exclusively, obviously as a result of di-π-methane rearrangement. No products resulting from a carbene species proposed to be involved in the di-π-methane reaction of triptycenes were detected. Thermolysis of compounds 3 gave not only compound 2 but also benz[a]aceanthrylene 4 and benz[a]indeno[1,2,3-cd]azulene 5 whose compositions were found to be sensitive to both the substituent (X) and the thermolysis temperature. Mechanisms of the reactions are discussed in terms of the relationship between the thermal and photochemical fragmentations.
- Tomioka, Hideo,Nakajima, Junichi
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p. 563 - 569
(2007/10/03)
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- Photochemistry of 9-Benzyloxytriptycenes
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The photochemical reactions of 9-benzyloxytriptycenes in methanol were found to give 2-(9-fluorenyl)benzaldehyde acetals and benzyl 2-(9-fluorenyl)phenyl ketones.Intermediacy of norcaradienes and two kinds of singlet carbenes has been demonstrated by quantum yields, light intensity dependence, competitive reactions, and substituent effects.
- Iwamura, Michiko,Mori, Eiko,Koike, Akemi,Kitagawa, Tomoko,Koga, Noboru,Iwamura, Hiizu
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p. 2051 - 2054
(2007/10/02)
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- Mechanisms of Condensation of Biaryl Hydrocarbons
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Results of kinetic studies of the condensed phase thermal reactions of the following biaryl hydrocarbons are reported; 1,1'-binaphthyl, 1,2'-binaphthyl, 1-phenylnaphthalene, and 9-phenylanthracene.Condensation generally occurred in parallel with both isomerization and dissociation and rates depended on concentrations of hydrogen donors.In order to simplify mechanisms, detailed studies used donors capable of providing just one H atom.These were xanthene, fluorene, and diphenylmethane.Condensation of 1,1'-binaphthyl in the presence of xanthene, the most effective donor, followed a second-order rate low (first order in both xanthene and binaphthyl concentration), k/M-1s-1=105.9+/-0.6exp(-36.0+/-2.0 kcal/RT)(360-560 deg C).Fluorene was one-fifth as effective as xanthene while diphenylmethane was nearly inert.A mechanism is proposed in which the key intermediates in all reactions are radicals created by H-atom transfer to the biaryls.In the condensation of naphthyl-containing biaryls, it is suggested that reactions are initiated by H transfer to a position next to the condensation site.Details of the unimolecular steps leading to condensation and isomerization, however remain unclear.Over the conditions studied, the reaction order with respect to donor varied between one and zero.It is proposed that this variability is a result of competition between two pathways for H transfer, one involving a simple, selective H transfer from the donor to a biaryl molecule, the other involving a free H-atom intermediate.
- Senthilnathan, V.P.,Stein, S.E.
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p. 3000 - 3007
(2007/10/02)
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