Metal‐Based Multihelicenic Architectures

Gauthier, Etienne S.; Rodríguez, Rafael; Crassous, Jeanne

doi:10.1002/ange.202004361

Cited by 16 publications

(2 citation statements)

References 69 publications

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“…In particular, the π‐conjugation on the graphenic structures can be modulated by nitrogen doping due to the lone pair of electrons provided [13] . It also allows the coordination with metals [14] or protons, [15,16] which will lead to ligands in supramolecular structures or acid‐responsive materials, respectively. For instance, it has been shown that the incorporation of pyrimidine [17] or pyridine [18] rings into the HBC skeleton not only modifies the electronic properties but also allows the modulation of their properties with pH variations.…”

Section: Introductionmentioning

confidence: 99%

N‐Doped Octagon‐Containing HBC as Redox and pH Chiroptical Switch in the NIR

Medel,

Hortigüela,

Lloveras

et al. 2023

ChemistryEurope

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The optical and chiroptical properties of an aza‐HBC‐oct‐[5]helicene have been studied and also modulated by means of protonation or oxidation. In both cases, the generated species shows a new absorption band in the NIR region that is not present in the neutral species. This result enables this N‐doped nanographene to act both as optical and, remarkably, as chiroptical switch since both the CD and CPL can be modulated by external stimuli such as redox or pH changes.

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Section: Introductionmentioning

confidence: 99%

N‐Doped Octagon‐Containing HBC as Redox and pH Chiroptical Switch in the NIR

Medel,

Hortigüela,

Lloveras

et al. 2023

ChemistryEurope

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“…Hence, enantiopure helicenes have been extensively applied as promising chiral materials for nonlinear optics, [1f,g, 3] chiral‐induced spin selectivity, [4] chiroptical switches, [5] and circularly polarized luminescence (CPL) [2g, 6] as well as for asymmetric catalysis, [7] etc. To date, structurally diverse optically active carbohelicenes and their analogues including heterohelicenes [1g, 2d,f,g] have been synthesized in a highly enantio‐ and/or diastereoselective manner through catalytic asymmetric reactions using chiral metal‐ and organocatalysts [1c,e, 8] and stereospecific reactions of optically active starting materials with point, axial, or planar chiralities [1c,e, 9] . Among them, the axially chiral biaryl derivatives have frequently been utilized as a powerful chiral auxiliary to control the helical geometry and handedness of the resulting carbo‐ and heterohelicenes since 1972 (Figure 1a).…”

Section: Introductionmentioning

confidence: 99%

Stereospecific Synthesis of Enantiopure [6]Helicene Containing a Seven‐Membered Ring and [7]Helicene by Acid‐Promoted Stepwise Alkyne Annulations of Doubly Axial‐Chiral Precursors**

et al. 2023

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Enantiopure [6]helicene containing an embedded seven‐membered ring and carbo[7]helicene (>99 % ee) with opposite helicity were simultaneously and quantitatively (>99 %) synthesized with a perfect stereospecificity through stepwise acid‐promoted intramolecular alkyne annulations of doubly axial‐chiral cyclization precursors. The helical handedness of the [6]‐ and [7]helicenes was fully stereocontrolled by the doubly axial chirality of the precursors as a result of complete axial‐to‐helical chirality transfer. The cyclizations proceeded in a stepwise manner; the first six‐membered ring formation was followed by the kinetically controlled seven‐ or six‐membered ring formation with or without helix‐inversion of a [4]helicene intermediate generated during the first cyclization step, thus quantitatively producing enantiopure circularly polarized luminescent [6]‐ and [7]helicenes with opposite helicity.

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Alkyne‐Based Syntheses of Carbo‐ and Heterohelicenes

Gulevskaya

Tonkoglazova

2022

Adv Synth Catal

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[n]Helicenes are polycyclic aromatic molecules in which n ortho‐condensed benzene or other aromatic rings give rise to helical chiral and highly conjugated structures. The unique screw shape, helically extended π‐system and intriguing electronic and chirooptical properties of these molecules have attracted scientific interest for decades. The applications of helicenes have now expanded into several fields including material science, nanoscience, biochemistry, supramolecular and polymer chemistry. Despite the great theoretical and practical interest in helicenes, their synthesis remains a challenge. Among synthetic approaches to helicenes, alkyne cyclizations have great potential, since carbon‐rich high‐energy alkynes can form aromatic rings via cycloisomerizations. These processes are atom‐economic. In addition, alkyne reactions are highly favorable thermodynamically. This review focuses on alkyne‐based syntheses of carbo‐ and heterohelicenes (2000–2022). These syntheses are obviously multistage. In the review, they are systematized in terms of the key step leading to the formation of a helical shape. The methods are grouped into two categories: (a) metal‐free syntheses and (b) transition‐metal‐catalyzed syntheses. This division is very arbitrary, since catalytic Sonogashira and Suzuki‐Miyaura reactions and others are often used to prepare starting materials in the syntheses of the first group. Most of the publications on the topic are related to transition‐metal‐catalyzed syntheses of helicenes.

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Metal‐Based Multihelicenic Architectures

Cited by 16 publications

References 69 publications

N‐Doped Octagon‐Containing HBC as Redox and pH Chiroptical Switch in the NIR

N‐Doped Octagon‐Containing HBC as Redox and pH Chiroptical Switch in the NIR

Stereospecific Synthesis of Enantiopure [6]Helicene Containing a Seven‐Membered Ring and [7]Helicene by Acid‐Promoted Stepwise Alkyne Annulations of Doubly Axial‐Chiral Precursors**

Alkyne‐Based Syntheses of Carbo‐ and Heterohelicenes

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