Switchable molecular tweezers: design and applications

• Pablo Msellem,
• Maksym Dekthiarenko,
• Nihal Hadj Seyd and
• Guillaume Vives

Beilstein J. Org. Chem. 2024, 20, 504–539, doi:10.3762/bjoc.20.45

• bonding with the two protonated [9]aneN3 units and two water molecules coordinated to the zinc center. More recently, terpyridine was also used by Crassous and co-workers to create a chiroptic switch (Figure 10) [49]. They synthesized tweezers 18 bearing helicene moieties as functional groups. The two

Perspectives on push–pull chromophores derived from click-type [2 + 2] cycloaddition–retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes

• Michio Yamada

Beilstein J. Org. Chem. 2024, 20, 125–154, doi:10.3762/bjoc.20.13

• optical resolutions of spirobifluorenes featuring two TCBD units located at the 2,2’-positions, designated as 54 [128]. Furthermore, Autschbach et al. prepared chiral carbo[6]helicene–TCBD derivatives 55 and 56 from enantiopure precursors [129]. For such intricate molecular systems, the presence of

• may not be apparent at a glance. Nevertheless, comprehensive computational analyses employing the matrix method suggest that the intense long-wavelength CD signal observed for 56 is due to the coupling of individual helicene-to-TCBD electric-transition dipole moments. The emergence of axial chirality

Construction of hexabenzocoronene-based chiral nanographenes

• Ranran Li,
• Di Wang,
• Shengtao Li and
• Peng An

Beilstein J. Org. Chem. 2023, 19, 736–751, doi:10.3762/bjoc.19.54

• chiral nanographenes. Keywords: chiral nanographene; helicene; racemization barrier; Scholl reaction; single-crystal X-ray diffractometry; Introduction Graphene, an allotrope of carbon, has captured widespread attention since it was first experimentally demonstrated as a monolayer of carbon atoms [1

• % yield. The Scholl reaction of compound 3 in the presence of FeCl3 and nitromethane led to the [5]helicene containing, seco-HBC-based chiral NG 4 in an 80% yield [33]. Miao and co-workers reported a twisted chiral NG 7 by a partially cyclized Scholl reaction. By treating compound 6 in 2,3-dichloro-5,6

• octagon-containing carbo[5]helicene was isolated in a 61% yield, which can be further transformed into other chiral hydrocarbon analogues 12 and 13 [35]. Chiral resolution of these helicenes was accomplished by chiral high-performance liquid chromatography (HPLC) and the isomerization barriers were

Thiophene/selenophene-based S-shaped double helicenes: regioselective synthesis and structures

• Mengjie Wang,
• Lanping Dang,
• Wan Xu,
• Zhiying Ma,
• Liuliu Shao,
• Guangxia Wang,
• Chunli Li and
• Hua Wang

Beilstein J. Org. Chem. 2022, 18, 809–817, doi:10.3762/bjoc.18.81

• packing structures of these compounds. Spectroscopic results and our previous work showed that the combination of molecular structure change and heteroatom replacement from S to Se could precisely modulate molecular energy levels. Keywords: crystal structure; double helicene; regioselective synthesis

• selenophene currently available, helicenes have received relatively little attention [27]. In our previous work, bull horn-shaped selenophene-based heteroacenes (1, Figure 1) and selenophene-based [7]helicene (2, Figure 1) were synthesized from the (TMS)2-substituted selenophene triacenes, 2,5-di

• (trimethylsilanyl)diseleno[3,2-b:2′,3′-d]selenophene ((TMS)2-tt-DSS) and (TMS)2-bb-DSS, respectively. In this work, the novel S-shaped double helicene DH-3 (Figure 1), which is based on selenophene units, was constructed as a new member of the selenohelicene family (Figure 1). In this synthetic study

Helicene synthesis by Brønsted acid-catalyzed cycloaromatization in HFIP [(CF₃)₂CHOH]

• Takeshi Fujita,
• Noriaki Shoji,
• Nao Yoshikawa and
• Junji Ichikawa

Beilstein J. Org. Chem. 2021, 17, 396–403, doi:10.3762/bjoc.17.35

• specific problems in conducting these synthetic reactions for large scale production (Scheme 1). For example, the Mallory reaction [12], which is a widely used photocyclization in helicene synthesis [13][14], requires high dilution or excess amounts of oxidizing agents to suppress intermolecular side

• reactions (Scheme 1a). Diels–Alder (Scheme 1b) [15] and radical reactions (Scheme 1c) [16] directed toward helicene synthesis require high temperature conditions even for low to moderate yields. Olefin metathesis (Scheme 1d) [17] and alkyne trimerization (Scheme 1e) [18][19] require the use of expensive

• this powerful cycloaromatization would be applicable to helicene synthesis. Thus, the following strategies were designed to establish a versatile method for the synthesis of helicenes (Scheme 3). Tandem cycloaromatization of bisacetals bearing a teraryl core was shown to be most effective for the one

Synthesis, crystal structures and properties of carbazole-based [6]helicenes fused with an azine ring

• Daria I. Tonkoglazova,
• Anna V. Gulevskaya,
• Konstantin A. Chistyakov and
• Olga I. Askalepova

Beilstein J. Org. Chem. 2021, 17, 11–21, doi:10.3762/bjoc.17.2

• were used as starting materials. To discern the effect of merging an azine moiety within a helical skeleton, the X-ray structures, UV–vis absorption and fluorescence spectra of the helicenes were investigated and compared to that of the parent carbazole-based [6]helicene (7H-phenanthro[3,4-c]carbazole

• acid as a cyclizing agent [72]. Unfortunately, only in the case of compound 9c, heating in trifluoroacetic acid led to isomerization into the required carbazole-based [6]helicene 10c (Table 5, entry 3). Under these conditions, alkynes 9a and 9b produced an unseparable mixture of some products. To our

• of the carbazole-based [6]helicene [42] (7-hexyl-7H-phenanthro[3,4-c]carbazole, 12) to see the effect of the azine ring annelation (Table 6). The values of the torsion and interplanar angles make it possible to describe and compare the structural specificity of the synthesized [6]helicenes. From the

Bipyrrole boomerangs via Pd-mediated tandem cyclization–oxygenation. Controlling reaction selectivity and electronic properties

• Liliia Moshniaha,
• Marika Żyła-Karwowska,
• Joanna Cybińska,
• Piotr J. Chmielewski,
• Ludovic Favereau and
• Marcin Stępień

Beilstein J. Org. Chem. 2020, 16, 895–903, doi:10.3762/bjoc.16.81

• measurements show that helicene-like boomerangs may be usable as circularly polarized luminescent materials. Keywords: donor–acceptor systems; double C–H bond activation; helicenes; pyrroles; Introduction Nanographenes and other polycyclic aromatics as well as their heterocyclic analogues are typically

• , and θ, the torsion angle between the two monopyrrole axes (Supporting Information File 1, Table S1). In contrast to the previously reported cR1O dilactams, which were nearly planar [32], systems with n = 2 and 3 are characterized by a twisting distortion, which produces helicene-like conformations

• emitters, provided that their helicene-like twist is further stabilized against racemization. Efforts to achieve this goal are currently ongoing in our laboratory. DFT-Optimized structures (B3LYP/6-31G(d,p)) of cNDA2O and cNMI3H. Absorption and emission spectra of cNMI2H (top) and cNMI3H (bottom) measured

Synthesis of triphenylene-fused phosphole oxides via C–H functionalizations

• Md. Shafiqur Rahman and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2020, 16, 524–529, doi:10.3762/bjoc.16.48

• from the side view, the triphenylene moiety slightly deviated from planarity, because the fusion with the phosphole ring caused a subtle steric repulsion between the phosphorus substituents and the triphenylene edge within the phospha[4]helicene moiety. Unlike many triphenylene derivatives, the crystal

Recent advances in photocatalyzed reactions using well-defined copper(I) complexes

• Mingbing Zhong,
• Xavier Pannecoucke,
• Philippe Jubault and
• Thomas Poisson

Beilstein J. Org. Chem. 2020, 16, 451–481, doi:10.3762/bjoc.16.42

• 2012, Collins and co-workers described a copper-catalyzed photocyclization to synthesize [5]helicene (Scheme 29) [43]. Using the in situ-formed [Cu(I)(dmp)(xantphos)]BF4 (25 mol %) in the presence of iodine and propylene oxide as the oxidant system under visible light irradiation, [5]helicene was

• ester derivatives. δ-Functionalization of alcohols using [Cu(I)(dmp)(xantphos)]BF4. Photocatalytic synthesis of [5]helicene and phenanthrene. Oxidative carbazole synthesis using in situ-formed [Cu(I)(dmp)(xantphos)]BF4. Copper-photocatalyzed functionalization of N-aryl tetrahydroisoquinolines. Bicyclic

Ruthenium-based olefin metathesis catalysts with monodentate unsymmetrical NHC ligands

• Veronica Paradiso,
• Chiara Costabile and
• Fabia Grisi

Beilstein J. Org. Chem. 2018, 14, 3122–3149, doi:10.3762/bjoc.14.292

• reported on the first example of a helically chiral Hoveyda-type metathesis complex. This catalyst, bearing a mesityl and a helicene as the aryl groups, was preliminary examined in some model asymmetric metathesis transformations and showed promising levels of enantioselectivity. Further studies on the

• use of any halide additive. The unsymmetrical NHC catalysts 164, 173 and 174 were also examined in the asymmetric synthesis of [7]helicene (180). Among them, complex 174 exhibited the highest degree of selectivity, leading to the desired product with an enantiomeric excess of 80% [56]. An extension of

A hemicryptophane with a triple-stranded helical structure

• Augustin Long,
• Olivier Perraud,
• Erwann Jeanneau,
• Christophe Aronica,
• Jean-Pierre Dutasta and
• Alexandre Martinez

Beilstein J. Org. Chem. 2018, 14, 1885–1889, doi:10.3762/bjoc.14.162

• interest [6][7][8]: for instance, Malik et al. described the synthesis and recognition properties of an organic cage including three helicene moieties in its arms [9]. This cage presents a triple stranded helical structure with the framework fully twisted due to the arrangement of the three helicene units

Synthesis of 1-indanones with a broad range of biological activity

• Marika Turek,
• Dorota Szczęsna,
• Marek Koprowski and
• Piotr Bałczewski

Beilstein J. Org. Chem. 2017, 13, 451–494, doi:10.3762/bjoc.13.48

• using 10% Pd/C (Scheme 73). An interesting example is the Diels–Alder reaction between dihydro-3-vinylphenanthrene (266) and 4-acetoxy-2-cyclo-penten-1-one (267) which led to formation of the helicene-like product 268 with the 1-indanone core (Scheme 74) [103]. The Diels–Alder reaction of 262 and

A facile synthesis of functionalized 7,8-diaza[5]helicenes through an oxidative ring-closure of 1,1’-binaphthalene-2,2’-diamines (BINAMs)

• Youhei Takeda,
• Masato Okazaki,
• Yoshiaki Maruoka and
• Satoshi Minakata

Beilstein J. Org. Chem. 2015, 11, 9–15, doi:10.3762/bjoc.11.2

• by conventional methodologies, would offer us many opportunities not only for creating helicene-based novel functional molecules but also uncovering missing pieces of unique aspects of helicenes. A bibliographic survey about helicenes led us focus on diazahelicenes having a diazene (–N=N–) moiety

• metal complexes through the coordination at the diazene unit [15][16][17]. Taking 7,8-diaza[5]helicene as an example, conventional methodologies of preparing such compounds (Scheme 2) involve i) reductive coupling of 2-nitronaphthalenes using strong reductants like Zn dust [1][18] and PH3 [19], ii

• only gave a trace amount of the corresponding diazahelicene [23]. In this connection, Caronna and co-workers have recently reported a simple protocol for synthesizing 7,8-diaza[5]helicene through oxidation of BINAM with mCPBA and following reduction of its oxides [24]. Although the method is high

Continuous flow photocyclization of stilbenes – scalable synthesis of functionalized phenanthrenes and helicenes

• Quentin Lefebvre,
• Marc Jentsch and
• Magnus Rueping

Beilstein J. Org. Chem. 2013, 9, 1883–1890, doi:10.3762/bjoc.9.221

• which are relevant for materials sciences, as well as toward helicenes, an intriguing class of molecules which show remarkable chiroptical properties due to their helical pitch. The rapidly expanding field of application of helicene-like molecules in materials sciences and optics demands the development

• of scalable and flexible syntheses [1][2][3][4][5]. Following the pioneering examples of Scholz [6] and Martin [7] in 1967, the photocyclization of stilbene derivatives under UV-light irradiation is now a classical method for the synthesis of phenanthrenes and helicene-like molecules [8]. However

• , the scalability of these reactions is limited by the required low concentration (~10−3 mol·L−1) and usually long reaction times (>20 h). Therefore, most of the applications of this method are limited to small scale (<0.5 mmol), making it unsuitable for gram-scale synthesis of helicene-like molecules

Flow photochemistry: Old light through new windows

• Jonathan P. Knowles,
• Luke D. Elliott and
• Kevin I. Booker-Milburn

Beilstein J. Org. Chem. 2012, 8, 2025–2052, doi:10.3762/bjoc.8.229

The interplay of configuration and conformation in helical perylenequinones: Insights from chirality induction in liquid crystals and calculations

• Elisa Frezza,
• Silvia Pieraccini,
• Stefania Mazzini,
• Alberta Ferrarini and
• Gian Piero Spada

Beilstein J. Org. Chem. 2012, 8, 155–163, doi:10.3762/bjoc.8.16

• is that which is expected for helicoidal disc-like dopants, as binaphthyl derivatives [20] and helicene-like molecules [22][24], i.e., left-handed for the M and right-handed for the P molecular helicity. In view of the similar molecular shape of 1 and 2, the difference between the absolute values of

Chiral amplification in a cyanobiphenyl nematic liquid crystal doped with helicene-like derivatives

• Alberta Ferrarini,
• Silvia Pieraccini,
• Stefano Masiero and
• Gian Piero Spada

Beilstein J. Org. Chem. 2009, 5, No. 50, doi:10.3762/bjoc.5.50

• efficient chiral inducers in biaryl nematic mesophases. In this paper, we focus on a new series of helicene-like molecules of known absolute configuration. We have integrated cholesteric pitch measurements with geometry optimization by DFT calculations and analysis of the twisting ability by the Surface

• , allows us to extend our knowledge of the molecular origin of the chirality amplification in liquid crystals and to confirm the simple relationship “molecular P-helicity” → “cholesteric P-handedness” for helical-shaped helicene-like derivatives. Keywords: chirality; cholesteric; helical twisting power

• ; helicene; nematic liquid crystal; Surface Chirality model; Introduction Nematic liquid crystals (LCs) are fluid phases formed by anisometric molecules which, though free to rotate as in ordinary liquids, are preferentially aligned along a common axis, called director. The addition of a chiral non-racemic