The Use of Cobalt‐Mediated Cycloisomerisation of Ynedinitriles in the Synthesis of Pyridazinohelicenes

Chercheja, Serghei; Klívar, Jiří; Jančařík, Andrej; Rybáček, Jiří; Salzl, Simon; Tarábek, Ján; Pospı́šil, Lubomı́r; Chocholoušová, Jana Vacek; Vacek, Jaroslav; Pohl, Radek; Cı́sařová, Ivana; Starý, Ivo; Stará̈, Irena G.

doi:10.1002/chem.201402312

Cited by 16 publications

(26 citation statements)

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“…92 Similarly, racemic helical pyridazines (including 2) were prepared by this method. 123 Scheme 17. Synthesis of 1,14-diaza [5]helicene by [2+2+2] Alkyne cyclotrimerization.…”

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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“…92 Similarly, racemic helical pyridazines (including 2) were prepared by this method. 123 Scheme 17. Synthesis of 1,14-diaza [5]helicene by [2+2+2] Alkyne cyclotrimerization.…”

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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“…To examine the preparation of parent pyridohelicenes, such as 7‐aza[5]helicene 14 exploiting this methodology, we synthesised cyanodiyne 12 by coupling iodide 9 with diyne 10 (for details, see the Supporting information) followed by desilylation of the protected cyanodiyne 11 (Scheme ). Here, the complex of Co I was found to be effective in cyclising 12 to 13 in high yield regardless of utilising irradiation with a halogen lamp or microwave reactor.…”

Section: Resultsmentioning

confidence: 99%

“…A feasibility of the [2+2+2] co‐cycloisomerisation of two alkynes with a nitrile stems from the fact (similarly to alkyne [2+2+2] cycloisomerisation) that the reaction is highly exergonic and, therefore, a steeply downhill pathway fuels the transition‐metal‐catalysed reaction. It can be demonstrated by the DFT calculated energetics of a proposed [2+2+2] co‐cycloisomerisation of the aromatic cyanodiyne 1 to dibenzopyrido[5]helicene 2 , which features a significant free‐energy release despite the introduction of an inherent torsional strain into the helical product (Scheme ) …”

Section: Introductionmentioning

confidence: 97%

“…Surprisingly, this well‐established synthetic methodology for the de novo construction of the pyridine ring has never been used, to the best of our knowledge, in the synthesis of pyridohelicenes. It is worth noting that only a cobalt‐mediated [2+2+2] co‐cycloisomerisation of ynedinitriles to helical pyridazines has been recently developed by us, and independently by Snyder et al…”

Section: Introductionmentioning

confidence: 99%

“… A proposed [2+2+2] co‐cycloisomerisation of aromatic cyanodiynes to pyridohelicenes. The free‐energy difference was calculated by DFT (B3LYP/cc‐pVTZ) in vacuo …”

Section: Introductionmentioning

confidence: 99%

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[2+2+2] Cycloisomerisation of Aromatic Cyanodiynes in the Synthesis of Pyridohelicenes and Their Analogues

Klívar

Jančařík

Šaman

et al. 2016

Chemistry A European J

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We have developed a methodology for the synthesis of pyridohelicenes and their analogues based on the Ni(0) -, Co(I) - or Rh(I) -mediated intramolecular [2+2+2] cycloisomerisation of cyanodiynes. It allows for folding the linear precursors into the corresponding helical backbones comprising the newly formed pyridine unit in their central part. Along with racemic pyrido[n]helicenes (n=5,6,7) and their derivatives, both enantio- and diastereomerically pure pyrido[n]helicene-like molecules (n=5,6) were prepared by employing the chiral substrate-controlled cyclisation of the corresponding enantiopure cyanodiynes.

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Structure and Property Diversity of Chiral Helicene Oligomers

Saito

Shigeno

Yamaguchi

2015

Encyclopedia of Polymer Science and Technology

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alkylthio, and perfluoroalkyl groups. In addition, cyclization of helicene oligomers provides another method of obtaining diversity.A notable aspect in the diversity of helicene oligomers is that they can be connected to provide multidomain oligomers (Fig. 4). When two helicene oligomers are connected, they are referred to herein as homo-bidomain oligomers. Cyclic homo-bidomain oligomers are also conceivable. Hetero-multidomain oligomers can be obtained by connecting different structures of oligomers. Such manipulations provide a large diversity of structures.Because helicene can generate characteristic π−π interactions, helicene oligomers often form bimolecular, trimolecular, tetramolecular, and polymolecular aggregates in which homoaggregation and heteroaggregation can also occur. Such aggregates self-assemble to form fibrils, vesicles, liquid crystals, and surface monolayers. These noncovalent bonding interactions provide diversity of the structure of helicene oligmers. Diverse Properties of Helicene OligomersStructural diversity is directly related to diversity of properties, and the properties of a helicene oligomer can be varied by structural modifications. In addition, multidomain oligomers can be designed, in which properties A and B of each domain can be combined. Such compounds exhibit property A + B or even another property C, a result regarded as the "synthesis of a property or function." Aggregation and self-assembly of helicene oligomers further increase property diversity, which covers materials with a broad range of sizes from subnanometersized molecules through nano-and micrometer-sized molecular aggregates and molecular self-assemblies to macroscopic bulk materials. Helicene oligomers are sensitive to changes in the environment such as temperature, solvent, and concentration. Different properties appear in dilute solution, in concentrated Amidohelicene oligomers: (a) acylcic oligomers (P)-1 (n = 1−9) with dianiline spacer, cyclic oligomers (P)-2 (n = 1−10) with dianiline spacer, (b) acyclic oligomers (P)-3 (n = 1−9) with m-phenylene spacer, and acyclic reverse oligomers (P)-4 (n = 1−4). (c) Schematic representation of reversible change between helix dimer and random coils of (P)-3 and (P)-4. solution, in the crystalline state, in the amorphous state, on the solid surface, at the solid-liquid interface, in fiber assemblies, in liquid crystals, and in gels. Dynamic properties of helicene oligomers are also interesting, and structural changes are largely affected by the environment, providing a stimulus response or possible molecular switching materials. It is also noteworthy that the process of a structure change can produce unusual transient phenomena. Amidohelicene OligomersStudies on helicene oligomers were initiated with amide derivatives (Fig. 5a, top), in which the spacer has a bent shape and includes both hydrogen bonding donor and acceptor moieties (24). (P)-5,8-Helicenedicarboxylate was reacted with bis(2,6-dimethylanilino)cyclohexane to give a series of acyclic helicene oligomers 1 up t...

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The Use of Cobalt‐Mediated Cycloisomerisation of Ynedinitriles in the Synthesis of Pyridazinohelicenes

Cited by 16 publications

References 46 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)

[2+2+2] Cycloisomerisation of Aromatic Cyanodiynes in the Synthesis of Pyridohelicenes and Their Analogues

Structure and Property Diversity of Chiral Helicene Oligomers

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