How to Lose a Bond in Two Ways ― The Diradical/Zwitterion Dichotomy in Cycloaromatization Reactions

Peterson, Paul W.; Mohamed, Rana K.; Alabugin, Igor V.

doi:10.1002/ejoc.201201656

Cited by 91 publications

(80 citation statements)

References 182 publications

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“…The question as to whether the Bergman cyclization could be forced to proceed in a different way has perplexed us for a long time until Alabugin et al [66,67] proposed a diradical/zwitterion dichotomy in cycloaromatization reactions. The Bergman cyclization is one of the cycloaromatization reactions which decouple two electrons by breaking two  bonds to form only one  bond.…”

Section: New Challengementioning

confidence: 99%

Recent advances of the Bergman cyclization in polymer science

Chen

2015

Sci. China Chem.

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The Bergman cyclization has strongly impacted on a number of fields including pharmaceutics, synthetic chemistry, and material science. The diradical intermediates stemmed from enediynes can not only cause DNA cleavage under physiological conditions but also function as monomer or initiator participants in polymer science. The homo-polymerization of enediynes through the Bergman cyclization to fabricate conjugated polymers is a fascinating strategy due to the advantages of facial operation, high efficiency, tailored structure, and catalyst-free operation. Moreover, conjugated polymers generated through the Bergman cyclization show many remarkable properties, such as excellent thermal stability, good solubility, and processability, which enables these polymers to be further manufactured into carbon-rich materials. Recent times have seen extensive efforts devoted to the application of the Bergman cyclization in polymer science and materials chemistry. A variety of synthetic strategies have been developed to fabricate structurally unique materials via the Bergman cyclization, including the fabrication of rod-like polymers with polyester, dendrimers and chiral imide side chains, functionalization of carbon nanomaterials by surface-grafting conjugated polymers, formation of nanoparticles by intramolecular collapse of single polymer chains, and the construction of carbon nanomembranes with different morphologies. Future developments involving the Bergman cyclization in polymer science, probably by altering the reaction mechanism to precisely control the microstructure of polymeric products, are also proposed in this review article.

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Section: New Challengementioning

confidence: 99%

Recent advances of the Bergman cyclization in polymer science

Chen

2015

Sci. China Chem.

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“…The 5‐ exo /6‐ endo selectivity can be explained by hyperconjugation of the alkyne π* orbital with the vinyl gold carbenoidic carbanion in 2 –Au during the transition state. In the case of terminal electron acceptors, the orbital coefficient favors exo attack, whereas with donor groups it favors endo attack …”

Section: Resultsmentioning

confidence: 99%

“…Note that the phospholium double bond in 2 –H is less nucleophilic than that in indoles, and therefore, its attack might be disfavored. In pathway 2, the mechanism proceeds through concerted diyne cyclization to generate a phenyl cation (e), which represents the zwitterionic version of the Bergmann cyclization . For the diyne mechanism, we anticipated a dramatic increase in the reaction velocity in the presence of free gold(I).…”

Section: Resultsmentioning

confidence: 99%

The Gold(I)‐Mediated Domino Reaction to Fused Diphenyl Phosphoniumfluorenes: Mechanistic Consequences for Gold‐Catalyzed Hydroarylations and Application in Solar Cells

Arndt

Borstelmann

Saatlo

et al. 2018

Chemistry A European J

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A domino sequence, involving a phosphinoauration and a gold-catalyzed 6-endo-dig cyclization step, was developed. Starting from modular and simple-to-prepare phosphadiynes, π-extended phosphoniumfluorenes were synthesized. The mechanistic proposal was supported by kinetic measurements and by the trapping of key intermediates. These led to important conclusions for the gold-catalyzed hydroarylation mechanism. Cyclic voltammetry (CV) and UV/Vis spectroscopy measurements indicated interesting properties for materials science. The phosphoniumfluorene structure was tested as a hole-blocking layer in perovskite solar cells of inverted architecture. Devices with the phosphoniumfluorene exhibited an efficiency of 14.2 %, which was much higher than that of devices without (10.7 %).

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“…3a). The known reaction of methanol with Myers-Saito reaction-derived α,3-dehydrotoluenes in similar fashion is also relevant 28,29,30 .…”

mentioning

confidence: 89%

The pentadehydro-Diels–Alder reaction

Wang

Naredla

Thompson

et al. 2016

Nature

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In the classic Diels–Alder (DA) [4+2] cycloaddition reaction1, the overall degree of unsaturation of the 4π (diene) and 2π (dienophile) pairs of reactants dictates the oxidation state of the newly formed six-membered carbocycle. For example, in the classic DA reaction, butadiene and ethylene combine to produce cyclohexene. More recent developments include variants in which the hydrogen atom count in the reactant pair and in the resulting product is reduced by2, for example, four in the tetradehydro-DA (TDDA) and by six in the hexadehydro-DA (HDDA3,4,5,6,7) reactions. Any oxidation state higher than tetradehydro leads to the production of a reactive intermediate that is more highly oxidized than benzene. This significantly increases the power of the overall process because trapping of the benzyne intermediate8,9 can be used to increase the structural complexity of the final product in a controllable and versatile manner. In this manuscript, we report an unprecedented net 4π+2π cycloaddition reaction that generates a different, highly reactive intermediate known as an α,3-dehydrotoluene. This species is at the same oxidation state as a benzyne. Like benzynes, α,3-dehydrotoluenes can be captured by various trapping agents to produce structurally diverse products that are complementary to those arising from the HDDA process. We call this new cycloisomerization reaction a pentadehydro-Diels–Alder (PDDA) reaction—a nomenclature chosen for chemical taxonomic rather than mechanistic reasons. In addition to alkynes, nitriles (RC≡N), although non-participants in aza-HDDA reactions, readily function as the 2π-component in PDDA cyclizations to produce, via trapping of the α,3-(5-aza)dehydrotoluene intermediates, pyridine-containing products.

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How to Lose a Bond in Two Ways ― The Diradical/Zwitterion Dichotomy in Cycloaromatization Reactions

Cited by 91 publications

References 182 publications

Recent advances of the Bergman cyclization in polymer science

Recent advances of the Bergman cyclization in polymer science

The Gold(I)‐Mediated Domino Reaction to Fused Diphenyl Phosphoniumfluorenes: Mechanistic Consequences for Gold‐Catalyzed Hydroarylations and Application in Solar Cells

The pentadehydro-Diels–Alder reaction

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