On the aromaticity and photophysics of 1-arylbenzo[a]imidazo[5,1,2-cd]indolizines as bicolor fluorescent molecules for barium tagging in the study of double-beta decay of ¹³⁶Xe

• Eric Iván Velazco-Cabral,
• Fernando Auria-Luna,
• Juan Molina-Canteras,
• Miguel A. Vázquez,
• Iván Rivilla and
• Fernando P. Cossío

Beilstein J. Org. Chem. 2025, 21, 1627–1638, doi:10.3762/bjoc.21.126

• a stabilization energy of ca. 17 kcal/mol. In the alternative hyperhomodesmotic reaction B, defined as 5 + 6 → 7 + 1, the formal ten-electron Hückel aromaticity of the imidazo[1,2-a]pyridine moiety (in blue) was preserved while the phenyl component was decomposed. The computed stabilization energy

• of this second reaction was calculated to be of 28 kcal/mol, slightly lower than the aromatic stabilization energy (ASE) and isomerization stabilization energy (ISE) calculated for benzene [20] (see reaction D in Scheme 1). Most likely this lowering stems from the strain imposed to the ortho

• -phenylene moiety in the tetracyclic structure. Combination of reactions A and B in the form yields an average value of ⟨ΔEAB⟩ = −22.6 kcal/mol. A similar treatment of the separate components as outlined in reactions C and D shows a much lower stabilization energy for imidazo[1,2-a]pyridine 8 and a higher

Transition-state aromaticity and its relationship with reactivity in pericyclic reactions

• Israel Fernández

Beilstein J. Org. Chem. 2025, 21, 1613–1626, doi:10.3762/bjoc.21.125

• further support to the barrier-lowering effect induced by the aromaticity of the transition state. While the purported ‘‘aromatic stabilization’’ is mainly established based on comparisons to transition states of alternative stepwise reaction routes, its extension to highly related processes following

• used in the synthesis of a good number of target molecules, including complex natural products [32][33][34][35]. Typically, the LA binds the dienophile through a donor–acceptor interaction (usually involving a carbonyl group) which results in a significant stabilization of the dienophile’s LUMO. As a

• aromatic species. Although aromaticity and energetic stabilization are traditionally connected in stable species (i.e., minima on the potential energy surface), it is found that processes featuring more asynchronous (less aromatic) transition states exhibit lower barriers than their more synchronous

Thermodynamic equilibrium between locally excited and charge transfer states in perylene–phenothiazine dyads

• Issei Fukunaga,
• Shunsuke Kobashi,
• Yuki Nagai,
• Hiroki Horita,
• Hiromitsu Maeda and
• Yoichi Kobayashi

Beilstein J. Org. Chem. 2025, 21, 1577–1586, doi:10.3762/bjoc.21.121

• the donor property but also to lower the energy of the LE state of the PTZ moiety. Notably, while PTZ adopts a non-planar conformation in the ground state, it undergoes planarization in the excited state [16][17]. This conformational change is expected to further enhance the stabilization effect

• imparted by TPA. Such stabilization could bring the energy levels of the LE state of the PTZ moiety and the CT state into closer proximity, which may create conditions favorable for establishing a transient thermal equilibrium between the LE and CT states. In this study, we designed and synthesized a

• driven by the enhanced electron-donating ability of the TPA units, but rather by the stabilization of the PTZ 1LE state, which is facilitated by planarization of the PTZ moiety in the excited state and the resulting increase in π-conjugation. This behavior led to the persistent presence of 1LE-state

pH-Controlled isomerization kinetics of ortho-disubstituted benzamidines: E/Z isomerism and axial chirality

• Ryota Kimura,
• Satoshi Ichikawa and
• Akira Katsuyama

Beilstein J. Org. Chem. 2025, 21, 1568–1576, doi:10.3762/bjoc.21.120

• axially chiral anilines [10][11] and a triazine molecule [9]. In particular, protonation of a remote basic site in N–C axially chiral anilines significantly increases the rotational barrier by attenuating resonance stabilization in the transition state. One important issue in this field is the development

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

• aza[n]helicenes 31g–j reveal |gabs| and |glum| values on the order of 10−3. These findings address long-standing challenges in the synthesis and stabilization of extended heterohelicenes, paving the way for the development of structurally persistent, π-extended chiral materials. In a parallel effort

• displays red-shifted emission and prolonged fluorescence lifetimes as solvent polarity increases, indicating enhanced excited-state stabilization. Collectively, these studies offer valuable strategies for stabilizing long π-extended helicenes and finely tuning their chiroptical and emissive properties

Tautomerism and switching in 7-hydroxy-8-(azophenyl)quinoline and similar compounds

• Lidia Zaharieva,
• Vera Deneva,
• Fadhil S. Kamounah,
• Nikolay Vassilev,
• Ivan Angelov,
• Michael Pittelkow and
• Liudmil Antonov

Beilstein J. Org. Chem. 2025, 21, 1404–1421, doi:10.3762/bjoc.21.105

• stabilization of the azo tautomer and making possible long range proton transfer to the quinolyl nitrogen atom. Keywords: azo dyes; E/Z isomerization; DFT; NMR; photochemistry; proton transfer; tautomerism; UV–vis; Introduction Azo compounds have long been utilized as dyes in industries such as textiles

• account in toluene E and KE are approximately equal as amount with a small presence (≈10%) of KK. The change of the solvent to acetonitrile does not change much the situation for the relatively equally polar E and KE, but leads to substantial stabilization of the more polar KK. The use of the relative

• reasons are different. While in acetonitrile this is the effect of the increased polarity of the solvent, leading to stabilization of the more polar keto tautomers, in the non-polar chloroform it is caused by its proton-donative nature (formation of a stabilizing intermolecular hydrogen bonding with the C

Supramolecular assembly of hypervalent iodine macrocycles and alkali metals

• Krishna Pandey,
• Lucas X. Orton,
• Grayson Venus,
• Waseem A. Hussain,
• Toby Woods,
• Lichang Wang and
• Kyle N. Plunkett

Beilstein J. Org. Chem. 2025, 21, 1095–1103, doi:10.3762/bjoc.21.87

• heteroatoms at axial positions resulting in a three-center four-electron bond [13][14]. In this unique “T” configuration, the bond length between iodine and one of the heteroatoms is influenced by the bond distance of the other heteroatom and is responsible for the stabilization of the hypervalent iodine

On the photoluminescence in triarylmethyl-centered mono-, di-, and multiradicals

• Daniel Straub,
• Markus Gross,
• Mona E. Arnold,
• Julia Zolg and
• Alexander J. C. Kuehne

Beilstein J. Org. Chem. 2025, 21, 964–998, doi:10.3762/bjoc.21.80

• -shaped distribution for ϕ. The bathochromic shift in λem has previously been described to result from the better stabilization of the CT excited state for stronger donors, and therefore a stabilization of the highest occupied molecular orbital (HOMO) when only considering the acceptor moiety (see also

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

• CT stabilization of the first excited state of the molecule [34]. This observation is further supported by the orthogonal D–A conformation calculated using DFT, which indicates a decoupled interaction between the HOMO and the LUMO (Figure 2). Moreover, compound 5e is the only member of the family in

Recent advances in controllable/divergent synthesis

• Jilei Cao,
• Leiyang Bai and
• Xuefeng Jiang

Beilstein J. Org. Chem. 2025, 21, 890–914, doi:10.3762/bjoc.21.73

• profound influence through multifaceted solute–solvent interactions [5]. Solvent polarity, hydrogen-bonding propensity, and dielectric characteristics collectively orchestrate stereodivergent pathways through dynamic coordination effects and differential stabilization of transition states. Notably, these

Light-enabled intramolecular [2 + 2] cycloaddition via photoactivation of simple alkenylboronic esters

• Lewis McGhie,
• Hannah M. Kortman,
• Jenna Rumpf,
• Peter H. Seeberger and
• John J. Molloy

Beilstein J. Org. Chem. 2025, 21, 854–863, doi:10.3762/bjoc.21.69

• differences in stereoelectronic stabilization of the transient 1,4-biradical intermediate on changing substituent (CO2R→BPin) [63][64][65]. It is pertinent to note that increased catalyst loading and reaction times were necessary for efficient reactivity with alkenylboronic esters, suggesting acrylates are

4-(1-Methylamino)ethylidene-1,5-disubstituted pyrrolidine-2,3-diones: synthesis, anti-inflammatory effect and in silico approaches

• Nguyen Tran Nguyen,
• Vo Viet Dai,
• Luc Van Meervelt,
• Do Thi Thao and
• Nguyen Minh Thong

Beilstein J. Org. Chem. 2025, 21, 817–829, doi:10.3762/bjoc.21.65

• interactions also contribute to the stabilization of the ligand–iNOS complexes. In particular, 4-(1-methylamino)ethylidene-5-phenyl-1-(3-nitrophenyl)pyrrolidine-2,3-dione (5e) exhibited the strongest binding affinity (−9.51 kcal/mol) and demonstrated significant inhibitory activity against nitric oxide (NO

• that all ligands consistently interacted with Cys200 and Ser242, key residues in the enzyme's active site, underscoring their critical role in ligand stabilization. In addition to hydrogen bonding, extensive van der Waals interactions were observed, particularly involving residues such as Thr190

• , Trp194, Gly202, Pro350, Phe369, and Tyr489, further contributing to the stabilization of the ligand–protein complexes. More importantly, the occurrence of an electron-withdrawing group, nitro group (NO2), on the aromatic ring linked to the 1-position of the pyrrolidine-2,3-dione core may help compound 5e

Recent advances in allylation of chiral secondary alkylcopper species

• Minjae Kim,
• Gwanggyun Kim,
• Doyoon Kim,
• Jun Hee Lee and
• Seung Hwan Cho

Beilstein J. Org. Chem. 2025, 21, 639–658, doi:10.3762/bjoc.21.51

• interactions and enhanced electronic stabilization through lithium coordination. This explains the critical role of lithium in achieving a high enantioselectivity. Isotope-labeling experiments using 10B-enriched 1,1-diborylalkanes (S)-49 further supported this mechanism, showing a stereoinvertive

Formaldehyde surrogates in multicomponent reactions

• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Bernhard Westermann

Beilstein J. Org. Chem. 2025, 21, 564–595, doi:10.3762/bjoc.21.45

• salts and TEMPO as the radical initiator/oxidant couple that promoted the intramolecular radical cyclization of suitable 1,3-dicarbonyl Ugi adducts 54 and 55 (Scheme 45) [108][109]. The stabilization of the enol in the 1,3-dicarbonyl Ugi adduct allows single-electron transfer (SET) with the anion

Beyond symmetric self-assembly and effective molarity: unlocking functional enzyme mimics with robust organic cages

• Keith G. Andrews

Beilstein J. Org. Chem. 2025, 21, 421–443, doi:10.3762/bjoc.21.30

• organized polarization rather than “confinement,” specifically positing that oriented electric fields rule transition-state stabilization for many reactions [33][34][35]. These fields stabilize charge redistribution during a reaction, usually at a small locus of each substrate molecule. It follows

• , therefore, that for redistribution penalties to be lessened, the equal and opposite stabilization must be granted to that same space. This is the basis of bifunctional/dual activation, as shown in Figure 1. Since very few reported supramolecular cavity designs provide bifunctional activation, cavity

• catalysis has fared best using approaches such as destabilizing ground states by constrictive binding, guiding molecular collisions to reduce large entropic costs (e.g., pericyclic reactions), and broad, undirected coulombic stabilization of charged transition states [36], for example of cations by

Unraveling aromaticity: the dual worlds of pyrazole, pyrazoline, and 3D carborane

• Zahra Noori,
• Miquel Solà,
• Clara Viñas,
• Francesc Teixidor and
• Jordi Poater

Beilstein J. Org. Chem. 2025, 21, 412–420, doi:10.3762/bjoc.21.29

• also applied to o-carboranes fused with five-membered ring systems [39][40]. The positioning of the heteroatom in these exo rings governs bonding, leading to restricted conjugation and, consequently, no aromatic stabilization. Importantly, the magnetic field generated by the 3D cluster influences the

Synthesis, structure, ionochromic and cytotoxic properties of new 2-(indolin-2-yl)-1,3-tropolones

• Yurii A. Sayapin,
• Eugeny A. Gusakov,
• Inna O. Tupaeva,
• Alexander D. Dubonosov,
• Igor V. Dorogan,
• Valery V. Tkachev,
• Anna S. Goncharova,
• Gennady V. Shilov,
• Natalia S. Kuznetsova,
• Svetlana Y. Filippova,
• Tatyana A. Krasnikova,
• Yanis A. Boumber,
• Alexey Y. Maksimov,
• Sergey M. Aldoshin and
• Vladimir I. Minkin

Beilstein J. Org. Chem. 2025, 21, 358–368, doi:10.3762/bjoc.21.26

• thermodynamically more stable than the corresponding (OH) forms. Increasing the polarity of the medium additionally enhances their stabilization. The introduction of an additional acceptor substituent to the tropolone moiety has a similar effect. In addition, compared to compounds 7a,b, compounds 8a,b show a marked

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

• ] reported a stable heptacene dication in concentrated sulfuric acid, a stability attributed to the intermolecular Coulomb repulsion between the charged molecules, which prevents the dimerization of the acene. This exciting finding suggests possible modes of kinetic stabilization of oxidized species of π

• report that compounds 1 and 2 can both be easily oxidized to form relatively stable radical cations (1•+, 2•+) and dications (12+, 22+). Interestingly, oxidation reverses local antiaromaticity to aromaticity, a transition that is particularly noticeable in 1 → 1•+ → 12+, where stabilization of the

• stabilization of such redox states. Results and Discussion Electrochemistry Figure 2 shows the electrochemical cyclic voltammograms of 1 and 2, in which two reversible oxidation processes can be observed. By considering the half-wave potential values obtained from the cyclic voltammograms, two one-electron

Synthesis of disulfides and 3-sulfenylchromones from sodium sulfinates catalyzed by TBAI

• Zhenlei Zhang,
• Ying Wang,
• Xingxing Pan,
• Manqi Zhang,
• Wei Zhao,
• Meng Li and
• Hao Zhang

Beilstein J. Org. Chem. 2025, 21, 253–261, doi:10.3762/bjoc.21.17

• groups in organic synthesis [1][2][3][4]. In chemistry and biology, disulfide bonds play crucial roles in protein folding and stabilization [5][6][7][8] and in the rubber industry, they are used to link different polymer chains [9][10]. The disulfide bond backbone is commonly used as a linker for

Recent advances in electrochemical copper catalysis for modern organic synthesis

• Yemin Kim and
• Won Jun Jang

Beilstein J. Org. Chem. 2025, 21, 155–178, doi:10.3762/bjoc.21.9

• enantioselectivity is the introduction of serine-derived bisoxazoline ligands L8 (sBOX). Upon coordination with a copper catalyst, these ligands present second-sphere ester groups, which facilitate the additional stabilization of noncovalent interactions at the penta-coordinated Cu(III) intermediate 82 in the

Efficient synthesis of fluorinated triphenylenes with enhanced arene–perfluoroarene interactions in columnar mesophases

• Yang Chen,
• Jiao He,
• Hang Lin,
• Hai-Feng Wang,
• Ping Hu,
• Bi-Qin Wang,
• Ke-Qing Zhao and
• Bertrand Donnio

Beilstein J. Org. Chem. 2024, 20, 3263–3273, doi:10.3762/bjoc.20.270

• effect of fluorinated rings and the decisive role of arene–fluoroarene interactions in both mesomorphism induction and stabilization. Thus, 2Li-BP was reacted with C6F5–C6F5 to produce 2-perfluorophenyl-1,3,4-trifluorotriphenylene (F), in 37% yield and 2,3,6,7-tetrakishexyloxy-10-phenyltriphenylene (BTP6

Surprising acidity for the methylene of 1,3-indenocorannulenes?

• Shi Liu,
• Märt Lõkov,
• Sofja Tshepelevitsh,
• Ivo Leito,
• Kim K. Baldridge and
• Jay S. Siegel

Beilstein J. Org. Chem. 2024, 20, 3144–3150, doi:10.3762/bjoc.20.260

• ; Loschmidt group element; molecular graph; Introduction A classic textbook tetrad linking hydrocarbon acidity to aromatic stabilization energy comprises cyclopentadiene (CpH), indene (InH), fluorene (FlH), and diphenylmethane (DPMH) [1][2], with pKa values in DMSO equal to 18 [3], 20.1 [3], 22.6 [3], and

• 32.2 [4], respectively (Scheme 1) [5][6]. The reaction enthalpy for deprotonation of CpH is ca 20 kcal/mol less endothermic than DPMH and ca. 24–27 kcal/mol less endothermic than 1,4-pentadiene (PDH; pKa ≈ 35 in DMSO) [3], values strikingly similar to the resonance stabilization energy estimated for

• benzene [7][8]. Furthermore, the trend of pKa values for CpH, InH, and FlH correlates with the reduction of the aromatic stabilization energy for the anion across the series [1][2]. At first glance, this model supports the notion that the relative pKa values of cyclopentadienes embedded in polynuclear

Cyclodextrin-based rotaxanes for polymer materials: challenge on simultaneous realization of inexpensive production and defined structures

• Yosuke Akae

Beilstein J. Org. Chem. 2024, 20, 3026–3049, doi:10.3762/bjoc.20.252

• the deslipping-based conversion process [46]. Moreover, considering the similar activation entropy values, the faster deslipping of [3]rotaxane was mainly caused by its lower activation enthalpy than that of [2]rotaxane owing to the stabilization effect derived from the inclusion structure formation

•  9C) [47]. Regarding the methoxy substituent, no inclusion formation was observed in the [2]rotaxane framework, whereas a shuttling motion of the wheel was observed on the axle moiety, indicating that a different stabilization effect was exerted based on the axle-end structures (Figure 9D). Such a

• stabilization effect could be affected by the bulkiness and polarity of the axle-end moieties. Meanwhile, the deslipping reaction of some [3]rotaxanes directly yielded the dumbbell and two wheels without any [2]rotaxane intermediate, indicating that the deslipping on [2]rotaxane proceeded faster than on [3

Deciphering the mechanism of γ-cyclodextrin’s hydrophobic cavity hydration: an integrated experimental and theoretical study

• Stiliyana Pereva,
• Stefan Dobrev,
• Tsveta Sarafska,
• Valya Nikolova,
• Silvia Angelova,
• Tony Spassov and
• Todor Dudev

Beilstein J. Org. Chem. 2024, 20, 2635–2643, doi:10.3762/bjoc.20.221

• cyclodextrin host, in contrast to β-CD where their interaction with the inner walls of the CD can be neglected and therefore does not contribute to the stabilization of water complexes. As a result of this different bonding, water molecules from γ-CD are released upon annealing in 2–3 successive stages

Photoredox-catalyzed intramolecular nucleophilic amidation of alkenes with β-lactams

• Valentina Giraldi,
• Giandomenico Magagnano,
• Daria Giacomini,
• Pier Giorgio Cozzi and
• Andrea Gualandi

Beilstein J. Org. Chem. 2024, 20, 2461–2468, doi:10.3762/bjoc.20.210

• . Across all tested substrates, nucleophilic attack predominantly occurred at the homobenzylic position, leading to the regioselective formation of clavam derivative with 2-benzylic substitution due to aryl stabilization of the radical intermediate (see mechanistic discussion below). We briefly

• •] = +2.09 V vs SCE) [55][56]. The *PC+ species can oxidize the unsaturated lactam, thereby producing the corresponding radical cation intermediate A. The low stabilization by amide-bond resonance of the cyclic four-membered β-lactam [57][58] ensures a good nucleophilicity of the nitrogen atom to efficiently