Rapid Access to Dibenzohelicenes and their Functionalized Derivatives

Jančařík, Andrej; Rybáček, Jiří; Cocq, Kévin; Chocholoušová, Jana Vacek; Vacek, Jaroslav; Pohl, Radek; Bednářová, Lucie; Fiedler, Pavel; Cı́sařová, Ivana; Stará̈, Irena G.; Starý, Ivo

doi:10.1002/anie.201301739

Cited by 150 publications

(81 citation statements)

References 59 publications

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“…92 The exploration of this synthetic strategy was pursued by the group of Stary and Stara and several helicenic systems were prepared in their racemic forms such as 1,14-diaza [5]helicene 124 and dibenzoaza [6]helicene. 125 Note that [2+2+2] cycloisomerization of either 3 alkynes (77a 1 ) or two alkynes and one nitrile (77a 2 ) can be performed and lead to different regioisomeric benzo-fused aza [6]helicenes, i.e. 78a 1 and 78a 2 , respectively (Scheme 19).…”

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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“…The bis‐benzo‐fused phospha[6]helicene P‐oxides 2 have been obtained as reported previously, via the Ni(0) promoted intramolecular cyclotrimerization of the triyne precursor ( R P )‐ 1 (Scheme ) . The method had been used initially by Stará and Starý for the synthesis of analogous carbo‐ and azahelicenes . In the presence of Ni(cod) 2 /PPh 3 the cyclotrimerization reaction takes place in high yields at room temperature.…”

Section: Resultsmentioning

confidence: 99%

Synthesis and X‐ray diffraction study of a chiral bis‐phosphahelicene palladium (II) complex

et al. 2019

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As a complement to our previous studies on the development of a class of chiral phosphahelicenes, this article discloses the synthesis, spectroscopic, and structural characterizations of a new phosphahelicene transition metal complex. It demonstrates the ability of these hindered chiral ligands to coordinate Pd (II) in trans‐complexes Cl2Pd(L*)2. In the solid state, the complex adopts a C2‐symmetric arrangement with two ligands facing each other on the same face of the coordination plane. X‐Ray data highlight bending of the Pd (II) unit from the expected planar coordination geometry that might be due to a significant π‐π stacking effect between the central rings of two helical units.

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“…[92] 2-Hydroxy-and 2,15-dihydroxyhexahelicenes could also be obtained, in their racemic forms, under nickel catalysis conditions. [97] The cycloaddition partners are obtained by a cross-coupling sequence and provide the desired cycloadducts with high enantioselectivities when reacting in the presence of the Ni(cod) 2 / (R)-Quinap catalytic system (Scheme 44). Improved nickel-catalyzed enantioselective synthesis of dibenzo [6]helicenes.…”

Section: Nickel Catalysismentioning

confidence: 99%

“…[96] More recently, asymmetric nickel-catalyzed cycloaddition of orthophenylene-tethered triynes has been used as a general approach to dibenzo[n]helicenes (n = 5, 6, 7). [97] The cycloaddition partners are obtained by a cross-coupling sequence and provide the desired cycloadducts with high enantioselectivities when reacting in the presence of the Ni(cod) 2 / (R)-Quinap catalytic system (Scheme 44). After simple recrystallization, the ee values could be improved to 99 %.…”

Section: Nickel Catalysismentioning

confidence: 99%

Recent Advances in Stereoselective [2+2+2] Cycloadditions

2014

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The [2+2+2] cycloaddition reaction is considered one of the most efficient methods for the rapid and straightforward preparation of complex polycyclic (and heterocyclic) compounds in a highly selective and atom‐economical fashion. Over the last half‐century, remarkable advances in terms of chemo‐ and regioselectivities have been realized, endowing this reaction with attractive features as a key step in the synthesis of various biologically active molecules and materials. The development of stereoselective methodologies is more recent. In this field, asymmetric transition‐metal catalysis has emerged as the most convenient tool with which to perform these [2+2+2] cycloadditions in their enantio‐ and diastereoselective variants. All the catalytic systems that have been developed so far are based on very close association of a transition metal (Co, Ni, Ir, Rh, ...) with a chiral ligand. The success of these reactions is then related to the reaction pattern involved (inter‐ and intramolecular), implying an efficient substrate/active species interaction. Thus, judicious design both of chiral ligands and of unsaturated substrates is necessary. In light of these aspects, numerous stereoselective cycloadditions have been reported; these allow the construction in one‐step fashion of central, axial, planar, and helical chiralities. This review details the recent advances in this area, with specific attention to catalysts and reaction scope.

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Rapid Access to Dibenzohelicenes and their Functionalized Derivatives

Cited by 150 publications

References 59 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)

Synthesis and X‐ray diffraction study of a chiral bis‐phosphahelicene palladium (II) complex

Recent Advances in Stereoselective [2+2+2] Cycloadditions

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