Advances in nitrogen-containing helicenes: synthesis, chiroptical properties, and optoelectronic applications

• Meng Qiu,
• Jing Du,
• Nai-Te Yao,
• Xin-Yue Wang and
• Han-Yuan Gong

Beilstein J. Org. Chem. 2025, 21, 1422–1453, doi:10.3762/bjoc.21.106

• extending into the near-infrared region, suggesting potential for redox-responsive chiral photonic systems. In 2023, Chen’s group reported three nitrogen–nitrogen (NN)-embedded azahelicenes 21a–c, among which compound 21c, a structurally defined antiaromatic double aza[7]helicene – exhibited distinctive

• BCPL value of 13.2 M−1 cm−1. Notably, compound 21c undergoes reversible redox interconversion to its radical cation 21c•+ and dicationic 21c2+ states via chemical oxidation, enabling controllable switching between antiaromatic and aromatic configurations. These results provide a compelling strategy for

• properties in helicene-based materials, advancing their applicability in next-generation optoelectronic devices. In 2020, Pittelkow’s group developed a unique synthetic strategy that converts a non-planar hetero[7]helicene into a planar hetero[8]circulene featuring an antiaromatic cyclooctatetraene (COT

Recent advances and future challenges in the bottom-up synthesis of azulene-embedded nanographenes

• Bartłomiej Pigulski

Beilstein J. Org. Chem. 2025, 21, 1272–1305, doi:10.3762/bjoc.21.99

• antiaromatic character of the pentagon, in contrast to pristine azulene. This results in a significantly red-shifted optical absorption at 997 nm. Therefore, compound 24 should be considered a formally antiaromatic extended indeno[1,2-b]fluorene, rather than a ‘true’ extended azulene. Similarly, Müllen and co

• products containing either two (63) or four azulene subunits (64). Analysis of NICS values revealed that the formally antiaromatic character indeno[1,2-b]fluorene units remain dominant in fused PAHs 63 and 64 resulting also in a biradical character. Considering these factors, PAHs 63 and 64 should be

• % yield. Despite the presence of four “formal azulene” units, the TPP (tetracyclopenta[cd,fg,jk,mn]pyrene) core of compound 66 exhibits antiaromatic properties. As a result, the pentagons within the structure remain antiaromatic, while the heptagons are non-aromatic, indicating the absence of an azulene

Study of tribenzo[b,d,f]azepine as donor in D–A photocatalysts

• Katy Medrano-Uribe,
• Jorge Humbrías-Martín and
• Luca Dell’Amico

Beilstein J. Org. Chem. 2025, 21, 935–944, doi:10.3762/bjoc.21.76

• -donating strength. The development of stronger donors to enhance luminescence remains a key area of research [20][21][22]. Recently, azepine-based analogs, such as tribenzo[b,d,f]azepine (TBA, a), have been explored due to their photoluminescence properties [23][24][25][26][27]. This antiaromatic core

• antiaromatic compound as an acceptor was previously reported (Figure 2) [31]. The dibenzo[b,d]thiophene 5,5-dioxide (5) was chosen for further investigation because of its red-shifted absorption. From a photochemical perspective, this characteristic can facilitate the use of less energetic light sources

• study the diverse or similar properties between the antiaromatic molecules a and b, in which the main difference is the presence of a third aromatic ring. According to the literature, the presence of the third benzene ring in the TBA (a) differentiates the conformations of structures a and b in the

Oxidation of [3]naphthylenes to cations and dications converts local paratropicity into global diatropicity

• Abel Cárdenas,
• Zexin Jin,
• Yong Ni,
• Jishan Wu,
• Yan Xia,
• Francisco Javier Ramírez and
• Juan Casado

Beilstein J. Org. Chem. 2025, 21, 277–285, doi:10.3762/bjoc.21.20

• radical cations and dications of linear and angular [3]naphthylenes, consisting of fused aromatic naphthalenoid and antiaromatic cyclobutadienoid moieties and containing different degrees of paratropicity. Electronic absorption and vibrational Raman spectroscopies were used to describe the more relevant

• bonding changes. Stretching force constants were evaluated to monitor the aromatic–antiaromatic alternation pattern upon oxidation. They showed us that the dication of linear [3]naphthylene became an overall global π-electron delocalized molecule. This result was supported by nucleus independent chemical

• -conjugated compounds that are unstable in their neutral ground-electronic states. According to the Hückel theory, antiaromatic molecules contain 4n π-electrons (n = 1, 2, 3…) and are highly unstable [8]. Though the antiaromatic molecules are much less common than their aromatic counterparts, they have

Radical reactivity of antiaromatic Ni(II) norcorroles with azo radical initiators

• Siham Asyiqin Shafie,
• Ryo Nozawa,
• Hideaki Takano and
• Hiroshi Shinokubo

Beilstein J. Org. Chem. 2024, 20, 1967–1972, doi:10.3762/bjoc.20.172

• Advanced Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan 10.3762/bjoc.20.172 Abstract Norcorrole is a stable 16π-antiaromatic porphyrinoid that exhibits characteristic reactivities and physical properties. Here, we disclose the reaction of Ni(II) norcorroles with alkyl

• ) norcorrole. The radical reactivity of Ni(II) norcorroles was investigated by density functional theory (DFT) calculations. Keywords: 16π; antiaromatic; norcorrole; porphyrinoid; radical; Introduction Considerable attention has been directed toward antiaromatic norcorroles [1][2][3] due to the fascinating

• antiaromatic character of the macrocycle changed to nonaromatic upon radical addition (see Supporting Information File 1). 1,1'-Azobis(cyclohexane-1-carbonitrile) (V-40) was also examined as a radical source. The reaction afforded 2b in 87% yield (Scheme 2). Unfortunately, other radical sources, such as

Hetero-polycyclic aromatic systems: A data-driven investigation of structure–property relationships

• Sabyasachi Chakraborty,
• Eduardo Mayo Yanes and
• Renana Gershoni-Poranne

Beilstein J. Org. Chem. 2024, 20, 1817–1830, doi:10.3762/bjoc.20.160

• -driven investigation of the newly generated COMPAS-2 dataset, which contains ~500k molecules consisting of 11 types of aromatic and antiaromatic rings and ranging in size from one to ten rings. Our analysis explores the effects of electron count, geometry, atomic composition, and heterocyclic composition

• new insights into these molecules. [Note: cata-condensed refers to fused PASs in which each atom participates in no more than two rings]. The second installment, COMPAS-2 [9], houses ~500k cata-condensed heterocyclic-PASs (cc-hPASs) comprising 11 types of aromatic and antiaromatic rings containing the

• in size, composition, and aromatic character: benzene, pyridine, pyrazine, borinine, 1,4-diborinine, 1,4-dihydro-1,4-diborinine, borole, pyrrole, furan, thiophene, and cyclobutadiene (Figure 1A). These building blocks encompass 6-, 5-, and 4-membered rings with aromatic and antiaromatic character

Biphenylene-containing polycyclic conjugated compounds

• Cagatay Dengiz

Beilstein J. Org. Chem. 2023, 19, 1895–1911, doi:10.3762/bjoc.19.141

• antiaromatic four-membered ring. This review gives a brief overview of the methods used in the synthesis of biphenylenes and summarizes the recent studies on biphenylene-containing polycyclic conjugated compounds, elucidating their synthesis, and distinct optoelectronic properties. Keywords: acenes

• benzene rings connected with a four-membered ring, is a highly intriguing compound in terms of its structure. It possesses a planar configuration and consists of 4n π-electrons, rendering it antiaromatic. However, despite being antiaromatic, biphenylene is more stable than other known antiaromatic

• compounds [12]. Research using computational methods to investigate how benzo and benzocyclobutadiene annulations impact the ring current density of biphenylene derivatives reveals that the antiaromatic (paratropic) current density in the 4-ring structure can range widely, shifting from highly antiaromatic

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

• benzannulation of diacetylene 42 in an 85% yield. The final NG 44 formed by treating compound 43 with DDQ/TfOH at 0 °C and the overall structure exhibits interesting photophysical and antiaromatic properties [45]. During the final Scholl reaction, an monoiodide structure 101 was also isolated (Scheme 11). In the

1,4-Dithianes: attractive C2-building blocks for the synthesis of complex molecular architectures

• Bram Ryckaert,
• Ellen Demeyere,
• Frederick Degroote,
• Hilde Janssens and
• Johan M. Winne

Beilstein J. Org. Chem. 2023, 19, 115–132, doi:10.3762/bjoc.19.12

• systems, as a wide range of α-halocarbonyl starting materials can be used in this scheme. 2 Reactivity of 1,4-dithiins as pseudo-aryl substrates Based on simple Hückel considerations for cyclic unsaturated hydrocarbons, 1,4-dithiin (3) could be considered as an antiaromatic compound [24]. For heterocycles

Introducing a new 7-ring fused diindenone-dithieno[3,2-b:2',3'-d]thiophene unit as a promising component for organic semiconductor materials

• Valentin H. K. Fell,
• Joseph Cameron,
• Alexander L. Kanibolotsky,
• Eman J. Hussien and
• Peter J. Skabara

Beilstein J. Org. Chem. 2022, 18, 944–955, doi:10.3762/bjoc.18.94

• , compound 6 features a quinoidal antiaromatic [10] structure. Antiaromaticity is reported to further decrease the energy gap. The electron-rich dithiole units provide an extended tetrathiafulvalene structure, leading to compound 7 exhibiting two reversible one-electron oxidations [25]. Fused thiophenes have

One-pot synthesis of dicyclopenta-fused peropyrene via a fourfold alkyne annulation

• Ji Ma,
• Yubin Fu,
• Junzhi Liu and
• Xinliang Feng

Beilstein J. Org. Chem. 2020, 16, 791–797, doi:10.3762/bjoc.16.72

• -diphenylpyrene is the key step. The single crystal X-ray diffraction analysis revealed a twisted structure of 1 due to the steric hindrance at the bay positions. From the bond length analysis and DFT calculations, CP-PAH 1 consists of the aromatic peropyrene core with two slightly antiaromatic peri-fused five

Design, synthesis and spectroscopic properties of crown ether-capped dibenzotetraaza[14]annulenes

• Krzysztof M. Zwoliński and
• Julita Eilmes

Beilstein J. Org. Chem. 2019, 15, 617–622, doi:10.3762/bjoc.15.57

• partially overlapped with proton resonances of aliphatic bridges. Receptor 3b displays the properties of chemical shift reagents, similar to the previously reported crown ether-capped porphyrin [36] but of different origin. Since, the macrocyclic dibenzotetraaza[14]annulene core is antiaromatic, and shows

Synthesis and characterization of π–extended “earring” subporphyrins

• Haiyan Guan,
• Mingbo Zhou,
• Bangshao Yin,
• Ling Xu and
• Jianxin Song

Beilstein J. Org. Chem. 2018, 14, 1956–1960, doi:10.3762/bjoc.14.170

• antiaromatic character of the ear-containing macrocycle, which is quite similar to the analogous “earring” porphyrin [38]. Furthermore, the antiaromaticity of the ear-containing macrocycle is proved by the large positive NICS value in the hole as well as the anticlockwise ring currency (see Supporting

• antiaromatic system as shown in Scheme 1. The cavity surrounded by the tripyrrin moiety owns a long axis of 4.229(4) Å and a short axis of 4.201(5) Å, which are almost the same. Despite of this the cavity is not circular because the three N atoms in the tripyrrin moiety and the nearest meso-C of the

• the metal does not change the antiaromatic pathways in 3. Fortunately we obtained single crystals of 3Pd from its CH2Cl2/CDCl3/MeOH solution via vapor diffusion. All of the bond lengths were carefully measured based on the diffraction results (Figure 4). We found that despite all peripheral C–C bond

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

• hydrochloride and afforded [11](2,6)-pyridinophane (37) (Scheme 3). Coupling reactions Castro–Stephens coupling: Youngs and co-workers [87] have synthesized p-methoxy-substituted tribenzocyclotriyne 39 using the Castro–Stephens coupling reaction (Scheme 4). Compound 39 is a planar antiaromatic dehydroannulene

Photoreactions of cyclic sulfite esters: Evidence for diradical intermediates

• Rick C. White,
• Benny E. Arney Jr. and
• Heiko Ihmels

Beilstein J. Org. Chem. 2012, 8, 1208–1212, doi:10.3762/bjoc.8.134

• loss of nitrogen from cyclic azo compounds is stepwise or concerted [6]. The photoextrusion of molecular nitrogen was employed also synthetically in the photoreaction of a benzothiadiazole to give an antiaromatic derivative of benzothiirene [7]. In another case, Griffin proposed carbene intermediates

Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues

• Helen Jansen,
• J. Chris Slootweg and
• Koop Lammertsma

Beilstein J. Org. Chem. 2011, 7, 1713–1721, doi:10.3762/bjoc.7.201

• NMR measurements showed that the slightly homoaromatic boat conformation is prone to undergo a degenerate ring flip via an antiaromatic C2v transition with a free energy barrier of 5.7 kcal·mol−1 in CBrF3 [18] and 6.3 kcal·mol−1 in CF2Cl2 [19][20][21]. Cycloheptatriene is in equilibrium with bicyclo

• ]. The calculated barrier of 8.3 kcal·mol−1 for thiepine (5) is nearly twice as large, possibly due to the higher antiaromatic destabilization of the flattened thiepine ring [40], but the interconversion of the boat forms of azepine and phosphepine are about equally favourable, requiring 3.0 [41] and 5.2

• thiepine and phosphepine are indeed highly antiaromatic planar 8π-electron systems, with positive NICS(1) values of 19.3 [47] and 6.4 ppm [7], respectively. The inherent instability of thiepine (5) has been attributed to this effect [51][52]. Oxepine – benzene oxide Oxepine (3) was isolated first by Vogel

Novel loop-like aromatic compounds: a further step on the road to nanobelts and nanotubes

• Venkataramana Rajuri,
• Dariush Ajami,
• Gaston R. Schaller,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2010, 6, No. 30, doi:10.3762/bjoc.6.30

• should be antiaromatic according to the Hückel rule. The chemical shifts of the olefinic protons in 2 (6.41 ppm) and 3 (6.49 ppm) are similar to those in 1 (6.45 ppm), which is typical for olefins and do not provide strong evidence for antiaromaticity. The crystal structures of 2 and 3 (Figure 1) confirm

• compounds 5b and 6 in 35% and 4% yield, respectively (Scheme 3) along with dimerization products of diene 10. Compound 6 is formed by a Woodward–Hoffmann symmetry allowed disrotatory electrocyclic ring opening of 5b. Compound 6 is formally a [16]annulene and therefore should be antiaromatic. However, the

• olefinic cis double bond forms dihedral angles of 69° and 79° (X-ray) with the two neighboring trans double bonds, and thus is twisted out of conjugation. Therefore, its antiaromatic character should be very small. The CS-symmetrical compound 5b and the approximately CS-symmetrical compound 6 were