Unsymmetrical sulfoxides with sterically hindered catechol fragment: synthesis, structure, electrochemical properties, and antiradical activity

• Daria A. Burmistrova,
• Vasiliy A. Fokin,
• Oleg P. Demidov,
• Mikhail A. Kiskin,
• Maxim V. Arsenyev,
• Andrey I. Poddel’sky,
• Nadezhda T. Berberova and
• Ivan V. Smolyaninov

Beilstein J. Org. Chem. 2026, 22, 828–837, doi:10.3762/bjoc.22.65

• ). Addition of the target catechols to a DPPH radical solution leads to a decrease in absorbance at the 517 nm maximum. The antiradical activities of CatH2-S-R and CatH2-SO-R were evaluated through the determination of IC50 and the time to reach the steady-state equilibrium (TEC50) values, together with the

Synthesis and structural elucidation of a novel bis-spirooxindole from isatin and ethylenediamine

• Irene Moreno-Gutiérrez,
• Josefa L. López-Martínez,
• Sonia Berenguel-Gómez,
• Irene Torres-García,
• Duane Choquesillo-Lazarte,
• Manuel Muñoz-Dorado,
• Miriam Álvarez-Corral and
• Ignacio Rodríguez-García

Beilstein J. Org. Chem. 2026, 22, 813–820, doi:10.3762/bjoc.22.63

• and 24 may coexist in equilibrium. The diimine 24 could also be in equilibrium with its tautomeric form 27. If the enol present in 27 attacks intramolecularly the other imine, it would produce a non-stabilised imine 28, which would be electrophilic and hence susceptible to reduction either by the

Knoevenagel condensation of 4,5- and 1,8-diazafluorenes

• Darya S. Cheshkina,
• Christina S. Becker,
• Alina A. Sonina and
• Maxim S. Kazantsev

Beilstein J. Org. Chem. 2026, 22, 803–812, doi:10.3762/bjoc.22.62

• mesomeric effect. On the other hand, diazafluorenes are potentially capable of reversible protonation by acetic acid, which is a competing process decreasing the equilibrium concentration of the enamine form (Scheme 2). Furthermore, an electrostatic repulsion between the protonated diazafluorene (1A/1A’ or

• ). Contrary, both the neutral (2) and protonated (2A’) forms of 1,8-diazafluorene were identified in both solvents (see Supporting Information File 1, Figure S2) with relatively high ratio (2 to 2A’ = 1:0.4 in CD3OD and 1:0.9 in CD3COOD). This equilibrium was reached immediately after the addition of the acid

• into 1,8-diazafluorenone by oxygen present in the reaction mixture. Therefore, the position of nitrogen atoms in diazafluorenes strongly affects their reactivity in acidic media via protonation, electrostatic repulsion, and stability of the condensation products. Therefore, the equilibrium in the

Synthetic study of vic-bromination of diarylacetylenes, easy purification and separation

• Akane Togo,
• Hiyono Suzuki,
• Yuto Akai,
• Makoto Matsumoto,
• Yoshinori Suzuma,
• Hidehiko Kodama and
• Kouichi Matsumoto

Beilstein J. Org. Chem. 2026, 22, 795–802, doi:10.3762/bjoc.22.61

• isomers are formed together might be due to the equilibrium between A and C, although there are many unknown points. Conclusion In summary, we have developed a simple and selective procedure of the synthesis of (E)-1,2-dibromo-1,2-diphenylethylene from diphenylacetylene by using NBS and FeBr3 in CH2Cl2

Hydrogen production from formic acid catalyzed by NHC–Cu complexes

• Orlando Santoro and
• Catherine S. J. Cazin

Beilstein J. Org. Chem. 2026, 22, 620–627, doi:10.3762/bjoc.22.48

• deprotonation of the acid; indeed, their coordination to the copper center must also be taken into account [45]. Moreover, the reaction between FA and amines occurs in a more complex manner than a common acid–base equilibrium. In fact, calorimetric studies on the formation of FA/triethylamine adducts showed

Modern synthetic pathways towards eribulin and its subunits

• Sebastian Dominik Graf

Beilstein J. Org. Chem. 2026, 22, 495–526, doi:10.3762/bjoc.22.37

• aldehyde motif (equilibrium of lactol to aldehyde and alcohol) was trapped by HWE reaction to obtain 95. The secondary alcohol unit of 95 was protected and the ester reduced to the respective alcohol, before Sharpless epoxidation, oxidation of the alcohol and subsequent Wittig reaction yielded allylic

• cyclization also considerable amounts of dimerized product were observed. Again, reduction with DIBAL-H led to the regioselective deprotection of the alcohols and reduction to an intermediate lactol unit, which is in equilibrium with its acyclic aldehyde and alcohol. The aldehyde was trapped by HWE reaction

• conditions, which led to a cyclization, and benzylated with BnBr towards 321. Stereoselective Michael addition of a Gilman reagent yielded 322. Reduction of the lactone unit yielded a lactol, which is in equilibrium with acyclic aldehyde and alcohol. The aldehyde was trapped via HWE reaction and the obtained

Synthesis and uranyl(VI) extraction performance of a calix[4]pyrrole–tetrahydroxamic acid receptor

• Sara Karnib,
• Rana Baydoun,
• Wissam Zaidan,
• Nancy AlHaddad,
• Omar El Samad,
• Bilal Nsouli,
• Francine Cazier-Dennin and
• Pierre-Edouard Danjou

Beilstein J. Org. Chem. 2026, 22, 486–494, doi:10.3762/bjoc.22.36

• . This time was estimated to be sufficient to reach equilibrium. The heterogeneous solution was centrifuged and the aqueous layer was filtered prior to gamma spectroscopy analysis. Uranium activity concentrations before and after extraction were determined, and extraction efficiencies were calculated

• uranyl ion and the Z-isomer of hydroxamic acid effectively shifts the Z/E equilibrium [70] towards the Z-conformation through a metal-induced fit mechanism [71][72]. Consistent with known hydroxamate coordination chemistry, coordination-induced deprotonation of the hydroxamic acid at low pH provides the

Arene activation via π-bond localization: concepts and opportunities

• Paul Meiners,
• Julian J. Melder and
• Tobias Morack

Beilstein J. Org. Chem. 2026, 22, 257–273, doi:10.3762/bjoc.22.19

• ]. Building on Kekulé’s early oscillation model for benzene, they proposed that small-ring annelation perturbs the equilibrium between the two assumed cyclohexatriene structures, shifting it to one side [17]. Although this original hypothesis was incorrect, its implications have been the topic of longstanding

• early example was reported by Stille and co-worker in 1978, who elegantly demonstrated the formation of an η3-benzyl–palladium complex via oxidative addition of Pd(0) to a benzyl halide (Scheme 5C) [73]. Detailed stereochemical and NMR analyses revealed a temperature- and solvent-dependent equilibrium

A mild and atom-efficient four-component cascade strategy for the construction of biologically relevant 4-hydroxyquinolin-2(1H)-one derivatives

• Dmitrii A. Grishin,
• Kseniia I. Sharkovskaia,
• Ilya G. Kolmakov,
• Daria A. Ipatova,
• Rostislav A. Petrov,
• Nikolai D. Dagaev,
• Dmitry A. Skvortsov,
• Maria G. Khrenova,
• Valeriy V. Andreychev,
• Sergei A. Evteev,
• Yan A. Ivanenkov,
• Roman L. Antipin,
• Olga А. Dontsova and
• Elena K. Beloglazkina

Beilstein J. Org. Chem. 2026, 22, 244–256, doi:10.3762/bjoc.22.18

• ; pyranoquinoline was the major product. Attempts at equilibrium transesterification using sodium isopropylate in isopropanol also failed to yield the desired product. Similar efforts to synthesize cyclohexyl esters via this approach were unsuccessful. Due to the inability to obtain the target isopropyl and

Conformational analysis of difluoromethylornithine: factors influencing its gas-phase and bioactive conformations

• Matheus P. Freitas

Beilstein J. Org. Chem. 2026, 22, 237–243, doi:10.3762/bjoc.22.17

• conformational stability. High-level DLPNO-CCSD(T)/CBS calculations revealed that type-I conformers – those maximizing gauche interactions between C–F and C–N bonds – dominate the equilibrium population, confirming the presence of the fluorine gauche effect. natural bond orbital (NBO) analysis showed that this

• account for about 62% of the equilibrium population. By contrast, type-II and type-III structures contribute only 7% and 0%, respectively (Figure 2). These results demonstrate that DFMO exhibits the gauche effect, unlike 1,1,2-trifluoroethane and 1,1,2,2-tetrafluoroethane, whose preferred geometries

• remains insufficient to overcome the stronger intermolecular interactions present in biological environments. Conclusion DFMO exhibits the fluorine gauche effect, as type-I conformers – those maximizing gauche interactions between the C–F and C–N bonds – dominate the conformational equilibrium by a large

Synthesis of diaryl phosphates using phytic acid as a phosphorus source

• Kazuya Asao,
• Seika Matsumoto,
• Haruka Mori,
• Riku Yoshimura,
• Takeshi Sasaki,
• Naoya Hirata,
• Yasuyuki Hayakawa and
• Shin-ichi Kawaguchi

Beilstein J. Org. Chem. 2026, 22, 213–223, doi:10.3762/bjoc.22.15

• groups [49][50][51][52], and thus phosphate esters easily undergo transesterification or hydrolysis reactions. Considering these factors, we assumed that shifting the reaction equilibrium of compounds derived from phenols containing strong electron-withdrawing groups toward phosphate diester formation

Design and synthesis of an axially chiral platinum(II) complex and its CPL properties in PMMA matrix

• Daiki Tauchi,
• Sota Ogura,
• Misa Sakura,
• Kazunori Tsubaki and
• Masashi Hasegawa

Beilstein J. Org. Chem. 2026, 22, 143–150, doi:10.3762/bjoc.22.7

• P-1030 polarimeter using the sodium D line (λ = 589 nm). All calculations were performed by using the Gaussian 16 rev C.02 program package. Density functional theory (DFT) calculations were performed at the level of CAM-B3LYP/LANL2DZ for Pt atoms. The optimized equilibrium structures were confirmed

Reactivity umpolung of the cycloheptatriene core in hexa(methoxycarbonyl)cycloheptatriene

• Dmitry N. Platonov,
• Alexander Yu. Belyy,
• Rinat F. Salikov,
• Kirill S. Erokhin and
• Yury V. Tomilov

Beilstein J. Org. Chem. 2026, 22, 64–70, doi:10.3762/bjoc.22.2

• dynamic equilibrium or total rearrangement of 5 into 6 upon formation. Thus, halogenation of hexa(methoxycarbonyl)cycloheptatrienyl anion 2 formed from 3 led to different outcomes with chlorine, bromine and iodine (Scheme 1). Chlorination gave exclusively i-substituted symmetric cycloheptatriene 4a in an

• halogenation reactions. The reactions with methyl iodide and propargyl bromide resulted in equilibrium mixtures of α-alkylated cycloheptatrienes 5d,e and the corresponding norcaradienes 6d,e. At the same time, benzyl bromide afforded pure norcaradiene 6f in a good yield. Apparently, the formation of a pure

Thiazolidinones: novel insights from microwave synthesis, computational studies, and potentially bioactive hybrids

• Luan A. Martinho,
• Victor H. J. G. Praciano,
• Guilherme D. R. Matos,
• Claudia C. Gatto and
• Carlos Kleber Z. Andrade

Beilstein J. Org. Chem. 2025, 21, 2618–2636, doi:10.3762/bjoc.21.203

• multiple tautomers (Scheme 7a) [37][39]. Relative stability of these tautomers is ranked as follows: 2-i > 2-ii > 2-iii > 2-iv > 2-v [74][75][76]. Therefore, compounds 3n and 4n may exist in equilibrium, with the enolic form being slightly more stable, which could explain the unusual behavior in their NMR

Efficient solid-phase synthesis and structural characterization of segetalins A–H, J and K

• Liangyu Liu,
• Wanqiu Lu,
• Quanping Guo and
• Zhaoqing Xu

Beilstein J. Org. Chem. 2025, 21, 2612–2617, doi:10.3762/bjoc.21.202

• , demonstrating unequivocal structural identity with the natural isolates. Analytical HPLC confirmed the high purity (>95%) of all synthetic segetalins. However, experimental data for segetalin C revealed the existence of a multi-state conformational equilibrium in solution, which is dependent on solvent polarity

Silica gel with covalently attached bambusuril macrocycle for dicyanoaurate sorption from water

• Michaela Šusterová and
• Vladimír Šindelář

Beilstein J. Org. Chem. 2025, 21, 2604–2611, doi:10.3762/bjoc.21.201

• concentration in solution reached equilibrium after 15 minutes, consistent with the equilibration time previously established for the non-covalent system SG-BnBU (Supporting Information File 1, Figure S5). Therefore, all subsequent sorption experiments were performed with an equilibration time of 15 minutes

Recent advances in total synthesis of illisimonin A

• Juan Huang and
• Ming Yang

Beilstein J. Org. Chem. 2025, 21, 2571–2583, doi:10.3762/bjoc.21.199

• reaction of 87 was employed, generating both the kinetic product 88 and the desired thermodynamic product 89. Heating 88 promoted a retro-Diels–Alder/Diels–Alder equilibrium, favoring the more stable isomer 89. Palladium-catalyzed hydrogenation of the 1,2-disubstituted alkene in 89, followed by Mo(CO)6

Ex-situ generation of gaseous nitriles in two-chamber glassware for facile haloacetimidate synthesis

• Nikolai B. Akselvoll,
• Jonas T. Larsen and
• Christian M. Pedersen

Beilstein J. Org. Chem. 2025, 21, 2465–2469, doi:10.3762/bjoc.21.188

• turned out to be unsuccessful as the reaction seemed to achieve an equilibrium, with some amount of hemiacetal left. Generally, it was observed that the trifluoroacetimidates were somewhat more sensitive to flash column chromatography, suggesting a higher reactivity compared to the trichloroacetimidates

The intramolecular stabilizing effects of O-benzoyl substituents as a driving force of the acid-promoted pyranoside-into-furanoside rearrangement

• Alexey G. Gerbst,
• Sofya P. Nikogosova,
• Darya A. Rastrepaeva,
• Dmitry A. Argunov,
• Vadim B. Krylov and
• Nikolay E. Nifantiev

Beilstein J. Org. Chem. 2025, 21, 2456–2464, doi:10.3762/bjoc.21.187

• development of a new methodology for the synthesis of galactofuranoside building blocks, we encountered an unexpected predominance of the furanoside form in the equilibrium mixture of benzoylated β-galactosides. Since the furanoside form is typically less stable and is usually present only in minor amounts

• equilibrium lie outside the carbohydrate ring system. Consideration of such effects is essential to rationalize the reactivity of structurally complex and densely protected carbohydrate compounds. Keywords: benzoylated galactofuranosides; DFT; DLPNO-CCSD(T); pyranoside-into-furanoside rearrangement

• pyranoside form is generally considered to be thermodynamically more stable [20][21][22]. Only several approaches towards shifting this equilibrium in favor for the galactofuranoside form are known, which are listed below. In one such study [23], the authors demonstrated a shift in the equilibrium towards a

Recent advances in Norrish–Yang cyclization and dicarbonyl photoredox reactions for natural product synthesis

• Peng-Xi Luo,
• Jin-Xuan Yang,
• Shao-Min Fu and
• Bo Liu

Beilstein J. Org. Chem. 2025, 21, 2315–2333, doi:10.3762/bjoc.21.177

• less favorable pathway compared to the previously employed 1,5-HAT. Initial feasibility studies revealed that the non-brominated substrate exhibited poor reactivity in the photochemical 1,6-HAT reaction (Scheme 14), as its unreactive conformer J dominated the equilibrium. In contrast, the brominated

Insoluble methylene-bridged glycoluril dimers as sequestrants for dyes

• Suvenika Perera,
• Peter Y. Zavalij and
• Lyle Isaacs

Beilstein J. Org. Chem. 2025, 21, 2302–2314, doi:10.3762/bjoc.21.176

• could be successfully fitted into the Langmuir isotherm model. Figure 7c shows a plot of the data fitted using Equation 2, where qe (mg g−1) represents the amount of methylene violet adsorbed at equilibrium, c (mol L−1) denotes the residual methylene violet concentration at equilibrium, and K (mol−1

• ) indicates the equilibrium constant. According to Figure 7c, the calculated maximum adsorption capacity (qmax,e) was estimated to be 1.32 mg g−1 (R2 = 0.9191) which is quite poor and corresponds to a 160:1 ratio of G2W1/methylene violet. This indicates that only a small portion of the potential adsorption

Halogenated butyrolactones from the biomass-derived synthon levoglucosenone

• Johannes Puschnig,
• Martyn Jevric and
• Ben W. Greatrex

Beilstein J. Org. Chem. 2025, 21, 2297–2301, doi:10.3762/bjoc.21.175

• demonstrated that halogenation reactions with 15 were viable, but dependent on the characteristics of the electrophile. To avoid the elimination of the amine, β-methyl ether 16 was prepared. The reaction of ketone 16 with Selectfluor promoted by ʟ-proline in MeOH/MeCN, which ensured that the equilibrium

A m-quaterphenyl probe for absolute configurational assignments of primary and secondary amines

• Yuka Takeuchi,
• Mutsumi Kobayashi,
• Yuuka Gotoh,
• Mari Ikeda,
• Yoichi Habata,
• Tomohiko Shirai and
• Shunsuke Kuwahara

Beilstein J. Org. Chem. 2025, 21, 2211–2219, doi:10.3762/bjoc.21.168

• at room temperature [41][42][43]. The central biphenyl moiety of conjugates 2a–h also rotates freely, forming an equilibrium mixture of P and M conformers. The relative amounts of P and M conformers depend on the chirality of the linked amine moieties. Figure 1a shows the UV and CD spectra of the

• central biphenyl moiety rotates freely, forming an equilibrium mixture of P and M conformers. Supporting Information Supporting Information File 9: Experimental procedures, characterization data including copies of NMR spectra (1H NMR, 13C NMR), CD spectra of (S)-2f and (R)-2f, theoretical calculations

C2 to C6 biobased carbonyl platforms for fine chemistry

• Jingjing Jiang,
• Muhammad Noman Haider Tariq,
• Florence Popowycz,
• Yanlong Gu and
• Yves Queneau

Beilstein J. Org. Chem. 2025, 21, 2103–2172, doi:10.3762/bjoc.21.165

• ) [71]. The Bobleter and Feather groups investigated the reaction mechanism of the conversion of these C3 compounds. The acid-catalyzed equilibrium between 1,3-dihydroxy-2-propane and 2,3-dihydroxypropanal involves an ene-triol intermediate which leads to methylglyoxal by a dehydration reaction at

• reported by Strizhov et al. [125]. The liable equilibrium transformation requires precisely pH-controlled conditions. In neutral medium, the furanone is in the form of its cis tautomer, while upon a slight increase in the pH, its cyclic original tautomer undergoes a ring opening with the formation of

• Meerwein–Ponndorf–Verley reduction, while acetaldehyde is generated in situ by ethanol oxidation (Scheme 50). The equilibrium allows furfural to be simultaneously converted into furfuryl alcohol and 3-(2-furyl)acrolein in one pot through a redox reaction. The highest mass conversion rate of furfural can

Understanding the origin of stereoselectivity in the photochemical denitrogenation of 2,3-diazabicyclo[2.2.1]heptene and its derivatives with non-adiabatic molecular dynamics

• Leticia A. Gomes and
• Steven A. Lopez

Beilstein J. Org. Chem. 2025, 21, 2007–2020, doi:10.3762/bjoc.21.156

• , experimentally, there is an ensemble of non-equilibrium geometries. To get a more realistic understanding of the absorption, we generated 500 geometries using the Wigner-sampling method to generate an ensemble of energetically accessible non-equilibrium geometries. We computed the gas-phase vertical excitation

• non-equilibrium assembled geometry produced a non-zero oscillator strength, unlike the optimized geometry, which exhibited zero. This difference is attributed to some mixing in the transition nature from S0 to S2, involving nNN(σCN) → Ryd and nNN → π* transitions. The S0 → S1 peaks from 316 to 319 nm

• ) [97][98][99][100] for 1, 3, and 5. The NAMD simulation was performed with the CASSCF(8,9)/ANO-S-VDZP method to elucidate the origin of stereoselectivities and the overall singlet-mediated mechanism involved in denitrogenation. We generated initial conditions with an ensemble of 700 non-equilibrium