Miscellaneous Applications of Helicenes: Surface Science and Asymmetric Catalysis

Crassous, Jérôme

doi:10.1002/9783527829415.ch16

Cited by 4 publications

(5 citation statements)

References 51 publications

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“…Multiple helicenes (MHs), 1 which are single molecules with multiple helicities, exhibit rich stereochemistry, namely, various stereoisomers with different three-dimensional structures and stereochemical dynamics for enantiomerization or diastereomerization. One notable structural feature of MHs is a highly distorted backbone, where some six-membered rings present a significant degree of out-of-plane deformation, endowing them with different (local) aromaticity and properties compared to planar polycyclic arenes and single helicenes.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Although these distinct structures were expected to deliver interesting stereochemistry, the molecular geometries have not been comprehensively analyzed and elucidated by single-crystal X-ray diffraction (sc-XRD). Based on the 1 diphenanthro[4,3-a:3′,4′-o]picene (BDPP), a prototype of these cooperative helicenes, consists of a chiral dl-double [7]helicene. However, the chiroptical properties have not been investigated.…”

Section: ■ Introductionmentioning

confidence: 99%

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Highly Distorted Multiple Helicenes: Syntheses, Structural Analyses, and Properties

et al. 2023

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A series of hexapole helicenes (HHs) and nonuple helicenes (NHs) were prepared from 1,3,5-tris[2-(arylethynyl)phenyl]benzene through two steps, namely, iodocyclization and subsequent palladium-catalyzed annulation with ortho-bromoaryl carboxylic acids. The crucial advantages of this synthetic method are the facile introduction of substituents, high regioselectivity, and efficient backbone extension. Three-dimensional structures of three C 1 -symmetric HHs and one C 3 -symmetric NH were elucidated using X-ray crystallography. Unlike most conventional multiple helicenes, the HHs and NHs investigated herein possess a unique structural feature where some double helical moieties share a terminal naphthalene unit. Chiral resolution of a HH and an NH was successfully achieved, and the enantiomerization barrier (ΔH ‡ ) of the HH was experimentally determined to be 31.2 kcal/mol. A straightforward method for predicting the most stable diastereomer was developed based on density functional theory calculations and structural considerations. It was found that the relative potential energies (ΔH r s) of all diastereomers for two HHs and one NH can be obtained using minimal computational effort to analyze the types, helical configurations, numbers, and ΔH (MP−MM) s [= H(M,P/P,M) − H(M,M/P,P)] of the double helicenyl fragments.

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Section: ■ Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Highly Distorted Multiple Helicenes: Syntheses, Structural Analyses, and Properties

et al. 2023

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“…Helicenes are ortho -fused polycyclic aromatic compounds in which benzene rings are angularly cyclized to create helical chirality. Since the twisted and helical skeletal structure shows unique physical properties derived from the nonplanar π-electron system, (asymmetric) synthesis of helicenes has been comprehensively studied in organic synthesis . While a carbohelicene consists of only carbons, a heterohelicene contains heteroatom(s) in the helical structure.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of Dithia[5]helicenes and Enantioselective Synthesis of Helically Chiral Thia[6]helicenes via Rh-Catalyzed Intramolecular [2 + 2 + 2] Cycloaddition of Triynes

et al. 2023

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Dithia[5]helicenes and helically chiral thia[6]helicenes were synthesized in high yields via a cationic Rh-catalyzed intramolecular [2 + 2 + 2] cycloaddition of triynes bearing sulfur-containing 1,6-diynes. Thia[6]helicene could be obtained with a high enantiomeric excess of P-isomers by using (S)-SEGPHOS as a chiral ligand. This protocol is the first example of the synthesis of thiahelicenes via [2 + 2 + 2] cycloaddition and can also be used for the asymmetric construction of an aza[6]helical skeleton.

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“…Helicene chemistry is a rapidly growing field − with applications to asymmetric catalysis, nonlinear optics, spin filters, switches and sensors, and the design of molecular machines . They can be synthesized with different sizes and are usually referred to as [ n ]helicenes, where n denotes the number of benzene rings.…”

Section: Introductionmentioning

confidence: 99%

X-ray and Optical Circular Dichroism as Local and Global Ultrafast Chiral Probes of [12]Helicene Racemization

Freixas,

Rouxel,

Nam

et al. 2023

J. Am. Chem. Soc.

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Chirality is a fundamental molecular property that plays a crucial role in biophysics and drug design. Optical circular dichroism (OCD) is a well-established chiral spectroscopic probe in the UV–visible regime. Chirality is most commonly associated with a localized chiral center. However, some compounds such as helicenes (Figure 1) are chiral due to their screwlike global structure. In these highly conjugated systems, some electric and magnetic allowed transitions are distributed across the entire molecule, and OCD thus probes the global molecular chirality. Recent advances in X-ray sources, in particular the control of their polarization and spatial profiles, have enabled X-ray circular dichroism (XCD), which, in contrast to OCD, can exploit the localized and element-specific nature of X-ray electronic transitions. XCD therefore is more sensitive to local structures, and the chirality probed with it can be referred to as local. During the racemization of helicene, between opposite helical structures, the screw handedness can flip locally, making the molecule globally achiral while retaining a local handedness. Here, we use the racemization mechanism of [12]helicene as a model to demonstrate the capabilities of OCD and XCD as time-dependent probes for global and local chiralities, respectively. Our simulations demonstrate that XCD provides an excellent spectroscopic probe for the time-dependent local chirality of molecules.

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Miscellaneous Applications of Helicenes: Surface Science and Asymmetric Catalysis

Cited by 4 publications

References 51 publications

Highly Distorted Multiple Helicenes: Syntheses, Structural Analyses, and Properties

Highly Distorted Multiple Helicenes: Syntheses, Structural Analyses, and Properties

Synthesis of Dithia[5]helicenes and Enantioselective Synthesis of Helically Chiral Thia[6]helicenes via Rh-Catalyzed Intramolecular [2 + 2 + 2] Cycloaddition of Triynes

X-ray and Optical Circular Dichroism as Local and Global Ultrafast Chiral Probes of [12]Helicene Racemization

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