Asymmetric Synthesis of Diastereo‐ and Enantiopure Bioxahelicene 2,2′‐Bipyridines

Klívar, Jiří; Jančařík, Andrej; Vacek, Jaroslav; Bednářová, Lucie; Budêšínský, Miloś; Fiedler, Pavel; Starý, Ivo; Stará̈, Irena G.

doi:10.1002/ejoc.201800541

Cited by 23 publications

(19 citation statements)

References 70 publications

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“…This nicely illustrates a point-to-helical chirality transfer utilizing a traceless chiral auxiliary. 128 Using similar strategies, the same group prepared pseudohelicenic 2,2′-bipyridines (91-95), 129 together with pseudohelicenic N-containing structures 96-98, 130 in almost diastereomerially pure forms ( Figure 14 and Table 7).…”

Section: [2+2+2] Alkyne Cyclotrimerizationmentioning

confidence: 99%

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

2019

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In this review, we discuss the rich chemistry of helicenes and helicenoids containing maingroup elements. Enantioenriched helicenic derivatives containing main-group elements B, Si, N and P, either incorporated within the helical backbone or grafted to it, will be thoroughly presented. We will describe their synthesis, resolution, and asymmetric synthesis, their structural features, electronic and chiroptical properties, emission, together with other photochemical properties and applications. OUTLINE 14 The absorption spectrum of 19c recorded in CH 2 Cl 2 solutions exhibited a maximum at 376 nm which is significantly red shifted compared with that of double [5]helicene 19a (310 nm) due to the more extended π-conjugation in 19c. According to TD-DFT calculations, the low-energy absorption band from 400 to 500 nm is assignable to the HOMO→LUMO transition corresponding to a π−π* transition of the fully conjugated bis-helical system. DFT calculations revealed a very high theoretical isomerization barrier of 45.1 kcal/mol for the (P,P)/(M,M)-19c stereoisomer, i.e. 4.4 kcal/mol higher than the (P,M) stereoisomer (not observed experimentally). The high configurational stability of 19c enabled to obtain the pure (P,P)and (M,M)-19c by chiral HPLC (Daicel Chiralcel IE column; EtOAc/MeOH = 9:1 as eluent) and to study their chiroptical properties. The ECD spectrum of (P,P)-19c in CH 2 Cl 2 displayed two strong positive bands at 275 and 320 nm, a strong negative one at 375 nm and a broad and less intense one between 425-475 nm. 52 Note that the isomerization barrier of the OBO-fused double [7]helicene is much higher than for oxabora[6]helicene 9 (vide supra) and higher than carbo[7]helicene (42.0 kcal/ mol), indicating the advantage of double helicenes over monohelicenes in terms of conformational stability. Indeed no racemization was observed upon heating enantiomer (P,P) and (M,M)-19c for 24 h up to 200 °C. 52 Note that in 2017 a longer double OBO-helicene analogue was deposited on a Au(111) under UHV conditions and its surface-assisted cyclodehydrogenation into a planar OBO-perihexacene was observed by STM. 54 Similarly to 6 and 9, the strong bond alternation found in the BOC4 rings of 19a 51 may account for the small NICS value of 1.3 while the surrounding C6 rings, including the distorted central benzene ring, show large negative NICS values (Scheme 3c). For comparison, in the all-carbon analogue tetrabenzo-[a,f,j,o]perylene shown in Scheme 3c, the central C6 ring shows a positive NICS value, indicating substantial antiaromatic character. Notably, molecular orbital calculations of 19a indicate that the HOMO and LUMO are spread over the C6 rings rather than on the boron and oxygen atoms, accounting for the substantial stability of 19a (Scheme 3c). Borahelicenes are efficient blue fluorophores. Indeed, azabora[6]helicene 6 displays blue fluorescence at 447 nm (Table 2), while smaller achiral [4]helicenic systems were successfully used as host materials in phosphorescent OLEDs with efficiencies better than the classical 4,4'...

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Section: [2+2+2] Alkyne Cyclotrimerizationmentioning

confidence: 99%

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

2019

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“…In addition, chiral two-layer helicenes have attracted much attention in material sciences [39,40]. In all of above known cases, for Wilkinson's ferrocene, a transition metal is needed to anchor two planes for designing two-layered chiral catalysts.…”

Section: Introductionmentioning

confidence: 99%

Multilayer 3D Chirality and Its Synthetic Assembly

Liu

Yang

et al. 2019

Research

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3D chirality of sandwich type of organic molecules has been discovered. The key element of this chirality is characterized by three layers of structures that are arranged nearly in parallel fashion with one on top and one down from the center plane. Individual enantiomers of these molecules have been fully characterized by spectroscopies with their enantiomeric purity measured by chiral HPLC. The absolute configuration was unambiguously assigned by X-ray diffraction analysis. This is the first multilayer 3D chirality reported and is anticipated to lead to a new research area of asymmetric synthesis and catalysis and to have a broad impact on chemical, medicinal, and material sciences in future.

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“…[61] As a substitute to racemate resolution, asymmetric synthesis (both catalytic and stoichiometric, stoichiometric synthesis for this case) of enantio-and diastereo-pure bioxa [5]helicene 2,2'bipyridine analogues described by Stara, Stary ́ ét al. [62] This method uses a tandem of [2+ 2+2] cycloisomerization of dicyanotetrayne or one-pot/sequential intramolecular [2+2+2] cycloisomerization of triyne followed by an intermolecular haloazaoxahelicene reductive homocoupling. The 1,3-allylic-type strain and sterically limited atropoisomerization of the embedded 2,2′-bipyridine unit control the central-to-helical-to-axial chirality transfer.…”

Section: Double [5]heterohelicenementioning

confidence: 99%

Recent Advances in Multiple Heterohelicenes

Shen

Yang

2022

Preprint

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Multiple heterohelicenes involing one or more heteroatoms in the helical backbone, in light of the importance of their spanning disciplines of the chemical and material sciences, have thus attracted significant interest from various research fields. In this review, we will specially concentrate on current progress in the chemistry of multiple heterohelicenes especially of those with boron, nitrogen, oxygen, silicon, or phosphorous atoms fused into the skeletons over the past decade (2012-2022). For each multiple heterohelicenes, their synthesis, structural features, electronic and chiroptical properties, as well as examples of their applications, are collected.

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Asymmetric Synthesis of Diastereo‐ and Enantiopure Bioxahelicene 2,2′‐Bipyridines

Cited by 23 publications

References 70 publications

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

Multilayer 3D Chirality and Its Synthetic Assembly

Recent Advances in Multiple Heterohelicenes

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