Inside Cover: Asymmetric Catalysis on the Nanoscale: The Organocatalytic Approach to Helicenes (Angew. Chem. Int. Ed. 20/2014)

Kötzner, Lisa; Webber, Matthew J.; Martínez, Alberto; Fusco, Claudia De; List, Benjamin

doi:10.1002/anie.201401125

Cited by 106 publications

(36 citation statements)

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“…Recent resurgence of interest in [ n ]helicenes, ortho -annelated polycyclic aromatic molecules with nonplanar helical conjugation of the π-electron system, has revitalized the efforts to develop more efficient synthetic methods and expansive applications . [ n ]Helicenes have become more accessible and modern synthetic methodologies have provided a variety of new [ n ]heterohelicenes, in which the embedded heteroatom(s) could provide additional functionalities. ,− While these developments greatly facilitate the design and synthesis of open-shell [ n ]helicene molecules, the detrimental reactivity of open-shell species remains the biggest impediment. The common, effective strategy for stabilizing open-shell species is to shield the radical site using bulky substituents, but it may be difficult to implement, as well as unappealing, in the design and synthesis of [ n ]helicenes.…”

Section: Introductionmentioning

confidence: 99%

Radical Cation and Neutral Radical of Aza-thia[7]helicene with SOMO–HOMO Energy Level Inversion

et al. 2016

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We report a relatively persistent, open-shell aza-thia[7]helicene with cross-conjugated electron-rich π-system. The singly occupied molecular orbital (SOMO) energy levels of both radical cation and neutral radical of the [7]helicene are below the highest occupied molecular orbital (HOMO) energy levels, thereby violating the Aufbau principle. The aza-thia[7]helicene is prepared from β-hexathiophene by a three-step one-pot reaction, in which the pyrrole ring is constructed by two consecutive C–N bond formations. Chemical oxidation converts the helicene to its radical cation, while in the presence of base (Cs2CO3), the oxidation gives neutral aminyl radical, likely via proton dissociation from the aminium radical cation with a low pK a. Reaction of the aza-thia[7]helicene with NaH provides the corresponding anion, which shows characteristic cyclic voltammetry wave at anodic peak potential E p a ≈ +0.2 V. Chemical oxidation of the anion with ferrocenium hexafluorophosphate at room temperature gives persistent neutral aminyl radical. Structure of the aza-thia[7]helicene is supported by NMR, IR, X-ray crystallography, and cyclic voltammetry. The radical cation and neutral radical are characterized by EPR and UV–vis-NIR spectroscopies. DFT computations of the radical cation and neutral radical predict the SOMO–HOMO energy level inversion, which is supported experimentally by electrochemical data for the radical cation.

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Section: Introductionmentioning

confidence: 99%

Radical Cation and Neutral Radical of Aza-thia[7]helicene with SOMO–HOMO Energy Level Inversion

et al. 2016

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“…Heterohelicenes with nitrogen as heteroatom, referred to as azahelicenes, can be of several types: pyridine-containing, pyridazine, pyrrole derivatives, etc. The pyrrole type is similar to the above molecules and has attracted some interest in recent years along with similar bis-azahelicene . A derivative of the former type aza[7]helicene V has been synthesized and studied for its photophysical properties, and it also shows remarkably high thermal stability .…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Photophysical Properties of Aza[n]helicenes

2016

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Synthesis and study of aza[7]helicene and aza[9]helicene is presented in this paper. Photo-dehydrocyclization of the 3,6-bis-styryl derivative of carbazole leading to sterically less demanding aza[7]helicene resulted in smooth reaction, and only the desired angular-angular product was detected. However, in the case of aza[9]helicene, along with the expected angular-angular cyclization, three other products involving linear mode of cyclization were also isolated and characterized. In this case, the helical compound aza[9]helicene was predominantly formed at lower concentration while the other isomers were obtained at higher concentration. All of the compounds formed by angular-angular, angular-linear, and linear-linear modes of cyclization were fully characterized, and their photophysical properties were investigated.

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“…Previously, our research group reported the enantioselective synthesis of 1,1′-bitriphenylene-based carbo-, phospha-, and sila[7]helicenes by the rhodium-catalyzed double [2+2+2] cycloaddition of a biphenyl-linked tetrayne with carbonyl-, phosphorus-, and silicon-linked diynes. − In a similar way, the present [2+2+2] cycloaddition was applied to the enantioselective synthesis of benzopicene-based helical molecules (Scheme ). The reactions of binaphtyl-linked tetrayne 7 and carbonyl-lineked diynes 8a , b proceeded at room temperature in the presence of the cationic rhodium(I)/( S )-H 8 –BINAP catalyst to give the corresponding benzopicene-based helical molecules 9a , b with high ee values, although the product yields were low.…”

Section: Results and Discussionmentioning

confidence: 97%

Synthesis, Structure, and Photophysical/Chiroptical Properties of Benzopicene-Based π-Conjugated Molecules

et al. 2017

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The convenient synthesis of substituted benzopicenes and azabenzopicenes has been achieved by the cationic rhodium(I)/H-BINAP or BINAP complex-catalyzed [2+2+2] cycloaddition under mild conditions. This method was applied to the synthesis of benzopicene-based long ladder and helical molecules. The X-ray crystal structure analysis revealed that the benzopicene-based helical molecule is highly distorted and the average distance of overlapped rings is markedly shorter than that in the triphenylene-based helical molecule. Photophysical and chiroptical properties of these benzopicene and azabenzopicene derivatives have also been examined. With respect to photophysical properties, substituted benzopicenes and azabenzopicenes showed red shifts of absorption and emission maxima compared with the corresponding triphenylenes and azatriphenylenes. With respect to chiroptical properties, the CPL spectra of the benzopicene-based helical molecule showed two opposite peaks, and thus the value of the CPL was smaller than that of the triphenylene-based helical molecule presumably due to the presence of two chiral fluorophores.

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Inside Cover: Asymmetric Catalysis on the Nanoscale: The Organocatalytic Approach to Helicenes (Angew. Chem. Int. Ed. 20/2014)

Cited by 106 publications

References 0 publications

Radical Cation and Neutral Radical of Aza-thia[7]helicene with SOMO–HOMO Energy Level Inversion

Radical Cation and Neutral Radical of Aza-thia[7]helicene with SOMO–HOMO Energy Level Inversion

Synthesis and Photophysical Properties of Aza[n]helicenes

Synthesis, Structure, and Photophysical/Chiroptical Properties of Benzopicene-Based π-Conjugated Molecules

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