Formation of 1,4-dibromo-2,3-benzobiphenylene, 2,3-benzobiphenylene, and 1,2,5,6-tetrabromo-3,4:7,8-dibenzotricyclo [4,2,0,02,5] octadiene

Jensen, Frederick R.; Coleman, William E.

doi:10.1016/s0040-4039(01)99477-8

Cited by 19 publications

(4 citation statements)

References 4 publications

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“…In an effort to uncover the simplest possible (nondegenerate) thermal migration of a phenyl group around the perimeter of a PAH diradical, we chose to examine the flash vacuum pyrolysis (FVP) of benzo[ b ]biphenylene ( 1 ) . At temperatures above 900 °C in the gas phase, two principal products are formed: indeno[2,1- a ]indene ( 2 ) and fluoranthene ( 3 ) (Scheme ). , The ratio of products 2 to 3 is 7:3 at 900 °C and 3:7 at 1100 °C. , Thus, isomerization to 2 is clearly favored at lower temperatures, but the pathway leading to 3 becomes dominant at higher temperatures.…”

mentioning

confidence: 99%

Phenyl Migrations in Dehydroaromatic Compounds. A New Mechanistic Link between Alternant and Nonalternant Hydrocarbons at High Temperatures

and

Scott

2000

Org. Lett.

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Flash vacuum pyrolysis of benzo[b]biphenylene, an alternant polycyclic aromatic hydrocarbon (PAH), gives fluoranthene, a nonalternant PAH, as the major product at 1100 degrees C in the gas phase. The most reasonable mechanism to explain this isomerization involves equilibrating diradicals of 2-phenylnaphthalene that rearrange by the net migration of a phenyl group to give equilibrating diradicals of 1-phenylnaphthalene, one isomer of which then cyclizes to fluoranthene.

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mentioning

confidence: 99%

Phenyl Migrations in Dehydroaromatic Compounds. A New Mechanistic Link between Alternant and Nonalternant Hydrocarbons at High Temperatures

and

Scott

2000

Org. Lett.

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“…The initial results on biphenylene and its more extensively fused counterparts led to another notable study conducted by Jensen and Coleman in 1959 [34]. By subjecting α,α,α′,α′-tetra- bromo-o-xylene (16) to t-BuOK to anhydrous conditions, biphenylene derivative 17 was obtained with a yield of 69% (Scheme 3).…”

Section: Phenylene-containing Oligoacenes (Poas)mentioning

confidence: 99%

Biphenylene-containing polycyclic conjugated compounds

Dengiz

2023

Beilstein J. Org. Chem.

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There has been a growing emphasis on the synthesis of polycyclic conjugated compounds, driven by their distinct structural characteristics that make them valuable candidates for use in cutting-edge technologies. In particular, acenes, a subgroup of polycyclic aromatic compounds, are sought-after synthetic targets due to their remarkable optoelectronic properties which stem from their π-conjugation and planar structure. Despite all these promising characteristics, acenes exhibit significant stability problems when their conjugation enhances. Various approaches have been developed to address this stability concern. Among these strategies, one involves the incorporation of the biphenylene unit into acene frameworks, limiting the electron delocalization through the antiaromatic four-membered ring. This review gives a brief overview of the methods used in the synthesis of biphenylenes and summarizes the recent studies on biphenylene-containing polycyclic conjugated compounds, elucidating their synthesis, and distinct optoelectronic properties.

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“…Beyond the importance of hydrogen shifts in radicals, such processes can also occur in diradicals produced by pyrolysis of metastable PAH precursors containing strained rings. Of particular interest here are hydrogen shifts resulting from pyrolysis of biphenylene-derived systems, including the conversion of linear [3]phenylene ( 3 ) to angular [3]phenylene ( 4 ), , the rearrangement of benzo[ b ]biphenylene ( 5 ) to fluoranthene ( 6 ), , and the rearrangement of angular [4]phenylene ( 7 ) to biphenylene dimer ( 8 ), , as shown in Scheme . The strain due to the four-membered rings makes the starting materials susceptible to C–C bond cleavage, producing aryl diradicals.…”

Section: Introductionmentioning

confidence: 99%

“…10,12,13 Beyond the importance of hydrogen shifts in radicals, such processes can also occur in diradicals produced by pyrolysis of metastable PAH precursors containing strained rings. Of particular interest here are hydrogen shifts resulting from pyrolysis of biphenylene-derived systems, including the conversion of linear [3]phenylene (3) 14 to angular [3]phenylene (4), 15,16 the rearrangement of benzo[b]biphenylene (5) 17 to fluoranthene (6), 18,19 Given the paucity of high-level computational and experimental mechanistic studies on these systems, we investigated hydrogen shift reactions in PAH radicals and diradicals using more sophisticated levels of theory. Here we report density functional and coupled cluster calculations aimed at elucidating the mechanisms and activation energies for the reactions in Scheme 3 and numerous monoradical model systems, and we address the following questions: (1) How does barrier height for hydrogen shifts in aryl radicals depend on chain length and C−H distance in the cyclic transition state?…”

Section: ■ Introductionmentioning

confidence: 99%

Hydrogen Shifts in Aryl Radicals and Diradicals: The Role of m-Benzynes

et al. 2017

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Density functional and coupled cluster results are presented for hydrogen shifts in radicals derived from polycyclic aromatic hydrocarbons (PAHs) and for rearrangement mechanisms for several phenylenes. RCCSD(T)/cc-pVDZ//UBLYP/cc-pVDZ free energy barriers for 1,4-H shifts at 298 K are consistently predicted to be ca. 25 kcal/mol, whereas barriers for 1,5- and 1,6-shifts range from 6 to 28 kcal/mol. The barriers correlate reasonably well with the distance from the radical center to the shifting hydrogen in the reactant. Proposed mechanisms (via diradical intermediates) of known rearrangements of linear [3]phenylene, benzo[b]biphenylene, and angular [4]phenylene have BD(T)/cc-pVDZ//(U)BLYP/cc-pVDZ computed barriers of 74-82 kcal/mol, consistent with pyrolysis temperatures of 900 to 1100 °C. Hydrogen shift reactions in most of the aryl diradicals arising from phenylenes produce m-benzyne intermediates which, despite being 8-15 kcal/mol more stable than other diradicals involved in the pathways, do not significantly lower the computed overall free energies of activation.

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Formation of 1,4-dibromo-2,3-benzobiphenylene, 2,3-benzobiphenylene, and 1,2,5,6-tetrabromo-3,4:7,8-dibenzotricyclo [4,2,0,02,5] octadiene

Cited by 19 publications

References 4 publications

Phenyl Migrations in Dehydroaromatic Compounds. A New Mechanistic Link between Alternant and Nonalternant Hydrocarbons at High Temperatures

Phenyl Migrations in Dehydroaromatic Compounds. A New Mechanistic Link between Alternant and Nonalternant Hydrocarbons at High Temperatures

Biphenylene-containing polycyclic conjugated compounds

Hydrogen Shifts in Aryl Radicals and Diradicals: The Role of m-Benzynes

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