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

• donor–acceptor dyads based on perylene (Pe) and phenothiazine (PTZ), in which triphenylamine (TPA) units and a phenyl spacer were introduced to modulate donor strength and spatial separation. Among the series, Pe–PTZ(TPA)2 exhibits a distinct thermal equilibrium between the locally excited (LE) state of

• the PTZ moiety and the photoinduced charge-transfer (CT) state. Femtosecond to microsecond transient absorption spectroscopy reveals that this equilibrium is facilitated not simply by enhanced donor ability, but presumably by excited-state planarization of the PTZ moiety, which lowers the energy of

• the LE state of the PTZ moiety. In contrast, Pe-Ph–PTZ(TPA)2, in which the donor–acceptor distance is increased by a phenyl spacer, does not show clear equilibrium behavior. These results underscore the crucial role of excited-state structural relaxation in tuning photoinduced charge separation, and

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

• switches [19]. For example, hydrazone-based molecular switches undergo reversible E/Z isomerization around the C=N bond [1][2][3][4][5][6][7], with protonation significantly shifting the equilibrium. Beyond double-bond isomerization, pH stimuli have also been employed to modulate rotational barriers in

Azobenzene protonation as a tool for temperature sensing

• Antti Siiskonen,
• Sami Vesamäki and
• Arri Priimagi

Beilstein J. Org. Chem. 2025, 21, 1528–1534, doi:10.3762/bjoc.21.115

• . We opted for methoxy substitution on one or both benzene rings as the simplest alkoxy substituent. The protonation of azobenzene (1), 4-methoxyazobenzene (2), and 4,4'-dimethoxyazobenzene (3) is schematized in Figure 1A. In the presence of a strong acid, these compounds form an equilibrium of neutral

• is assumed. Stronger electron donation gives rise to larger red-shift, and hence more pronounced color changes, upon protonation, as illustrated in Figure 1C. Figure 1D illustrates the shift in protonation equilibrium with increasing acidity when MSA is added to DCE solution of 3 at 25 °C. Due to the

• equilibrium constant (K) can be determined using Equation 1, provided that the reaction stoichiometry (n) is known. To determine the stoichiometry, the degree of protonation was measured for different acid concentrations and the corresponding K values were calculated. Using these K values, ∆G° can be

Highly distinguishable isomeric states of a tripodal arylazopyrazole derivative on graphite through electron/hole-induced switching at ambient conditions

• Himani Malik,
• Sudha Devi,
• Debapriya Gupta,
• Ankit Kumar Gaur,
• Sugumar Venkataramani and
• Thiruvancheril G. Gopakumar

Beilstein J. Org. Chem. 2025, 21, 1496–1507, doi:10.3762/bjoc.21.112

• electronic and optical properties of switchable states. The applicability of molecular switches relies on the efficiency, reversibility, and the half-life associated with different non-equilibrium states. Typically, the half-life of the Z isomer of AB is a few days [17]. Chemical modifications of AB

• be attributed to the electronically decoupled individual photoswitchable units by 1,3,5-functionalization and attainment of non-planar geometry [30]. Molecular switches with multiple switching units having extended lifetime for their non-equilibrium states will be a unique tool for fabricating multi

• -functional molecular switches on the surface. Molecular switches with multiple switching units are scarce on the surface [10][31] and mostly studied under low temperatures. If such multi-functional molecular switches, with stable non-equilibrium states, can be reversibly switched under ambient conditions

Wittig reaction of cyclobisbiphenylenecarbonyl

• Taito Moribe,
• Junichiro Hirano,
• Hideaki Takano,
• Hiroshi Shinokubo and
• Norihito Fukui

Beilstein J. Org. Chem. 2025, 21, 1454–1461, doi:10.3762/bjoc.21.107

• exist as an equilibrium mixture, in which the bathtub conformation is rather preferable at low temperature. Mono-olefin 3 and bis-olefin 5 exhibit enhanced configurational persistency compared to CBBC 1. Bis-olefin 5 fluoresces with a quantum yield of 7.5%, while CBBC 1 is non-emissive under ambient

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

• . without the ability to form hydrogen bonding with the solute) shifts the equilibrium in direction of the keto tautomer [57]. According to the theoretical data, collected in Table 1, the enol form of 2 is substantially more stable and should predominantly exist in toluene. In acetonitrile some traces of KE

• equilibrium towards C=O-group-containing structures. In addition, the spectra in the remaining solvents show a single band around 500 nm independent on the nature of the solvent. Obviously, these data cannot be interpreted in the frame of the concept for a tautomeric equilibrium. The rotor in 2 contains a OH

• of its existing amount and, consequently, to rise of the absorption band at around 470 nm and restoration with the time of the equilibrium tautomeric state. No appearance of K is expected as a result of higher energy as discussed previously. Actually, the third process is shown in Figure 7. Upon

Selective monoformylation of naphthalene-fused propellanes for methylene-alternating copolymers

• Kenichi Kato,
• Tatsuki Hiroi,
• Seina Okada,
• Shunsuke Ohtani and
• Tomoki Ogoshi

Beilstein J. Org. Chem. 2025, 21, 1183–1191, doi:10.3762/bjoc.21.95

• of [4.3.3]_branch showed multistep uptake. In the desorption step, both samples retained most of the adsorbed N2 molecules even at 30 kPa. These observations and slow equilibrium in the adsorption processes suggested that presence of narrow connections between molecular-size cavities disturbed smooth

Recent advances in synthetic approaches for bioactive cinnamic acid derivatives

• Betty A. Kustiana,
• Galuh Widiyarti and
• Teni Ernawati

Beilstein J. Org. Chem. 2025, 21, 1031–1086, doi:10.3762/bjoc.21.85

• acid chloride 36. On the other hand, Ma and co-workers (2019) converted cinnamic acids to the corresponding amides 37 and 38 in good yields via the active acyloxyphosphonium iodide species 39 in equilibrium with the acid iodide 40 (Scheme 13) [45]. Subsequently, 39/40 was coupled with 41 prepared via

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

• have produced y0 = 0.3 for the non-chlorinated Thiele diradical [92]. Interestingly, the Thiele hydrocarbon without chlorination in the meta-positions of the four peripheral phenyl-rings (TTH), exhibits higher y0 of up to 0.4, indicating the mesomeric equilibrium to be further on the open-shell side

Cu–Bpin-mediated dimerization of 4,4-dichloro-2-butenoic acid derivatives enables the synthesis of densely functionalized cyclopropanes

• Patricia Gómez-Roibás,
• Andrea Chaves-Pouso and
• Martín Fañanás-Mastral

Beilstein J. Org. Chem. 2025, 21, 877–883, doi:10.3762/bjoc.21.71

• species A which is in equilibrium with the Cu–O enolate B [11]. In the presence of excess of LiOt-Bu, a salt metathesis reaction between this base and intermediate B generates lithium enolate C and LCuOt-Bu to close the copper catalytic cycle. The formation of a lithium enolate is consistent with the

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

• interactions to achieve directionality (E→Z), synonymous with conventional photocatalyzed isomerization processes [19], it serves as a rapid reaction probe to support sensitization via the generation of a photostationary state equilibrium. The use of Ir(ppy)3 (Table 1, entry 1), an efficient sensitizer for the

• state catalyst are not operational (see Supporting Information File 1 for full details), providing support for an EnT mechanism, while exposing the Z-isomer (Z)-1a to the model reaction conditions, led to the generation of a similar photostationary state equilibrium of isomers, characteristic of an EnT

• . Probing boron effects on reactivity (A) and confirming the generation of a photostationary state equilibrium (B). Standard reaction conditions: (E)-1 (0.1 mmol), xanthone (5 mol %), MeCN (0.03 M), rt, 16 h. Probing EnT catalysis enabled [2 + 2] cycloaddition of simple alkenylboronic esters. Establishing

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

• positively charged nitrogen atom is broken heterolytically, leading to the final pyrrolidine-2,3-dione derivatives 5a–e and 4-methoxybenzylamine (Scheme 3). Due to the higher basicity of methylamine as compared to 4-methoxybenzylamine [25], the transimination equilibrium is shifted towards product 5a–e and

Development and mechanistic studies of calcium–BINOL phosphate-catalyzed hydrocyanation of hydrazones

• Carola Tortora,
• Christian A. Fischer,
• Sascha Kohlbauer,
• Alexandru Zamfir,
• Gerd M. Ballmann,
• Jürgen Pahl,
• Sjoerd Harder and
• Svetlana B. Tsogoeva

Beilstein J. Org. Chem. 2025, 21, 755–765, doi:10.3762/bjoc.21.59

• ), is 0.5 kcal·mol−1 lower in energy. Substrate 1 may conceivably undergo a tautomerization towards an iminol form, 14.2 kcal·mol−1 higher in energy. Hence, amounts of this isomer are negligible in equilibrium and do not play a role also in the formation of the pre-complex 3. The competing cyanide form

• -hydrazones, respectively. A thermodynamic control of the reaction outcome (i.e., especially enantioselectivity) would require the possibility to approach an equilibrium between 9 and 10 (seeing the reversibility of step 9 → 10), in which case the relative energies of stereoisomeric forms of 10 determine the

• experimentally achievable ee values. Maximal theoretical ee values are 70% "S" for Z-hydrazone and 70% "R" for E-hydrazone. The relatively high racemization barriers in 9 preclude a Curtin–Hammett scenario (with fast pre-equilibrium), which would otherwise render the enantiomeric outcome (ee value) independent

Acyclic cucurbit[n]uril bearing alkyl sulfate ionic groups

• Christian Akakpo,
• Peter Y. Zavalij and
• Lyle Isaacs

Beilstein J. Org. Chem. 2025, 21, 717–726, doi:10.3762/bjoc.21.55

• is flexible and the two senses of helicity – and other conformations – undergo rapid equilibrium rendering the C1 and the C1·Me6CHDA complex achiral. The centroids of the aromatic sidewall are 0.9698 Å (1.1193 Å) above and 1.3090 Å (1.4832 Å) below the mean plane of the glycoluril methine and

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

• formaldehyde and ammonia in situ by heating [83]. Under these conditions, the water present in hydrated HMTA is sufficient for this hydrothermal decomposition to occur. On the other hand, an excess of ammonia must be added to the reaction mixture to shift the equilibrium towards the imine. Using this procedure

Organocatalytic kinetic resolution of 1,5-dicarbonyl compounds through a retro-Michael reaction

• James Guevara-Pulido,
• Fernando González-Pérez,
• José M. Andrés and
• Rafael Pedrosa

Beilstein J. Org. Chem. 2025, 21, 473–482, doi:10.3762/bjoc.21.34

• the kinetic resolution at a concentration of approximately ten millimolar (mM) to prevent the Michael retro-Michael equilibrium from affecting the process. Keywords: 1,5-dicarbonyl; equilibrium; kinetic resolution; organocatalysis; retro-Michael; Introduction For many years, enantiomers have been

• racemization when treated with inorganic bases [25], which had led us to check the equilibrium between Michael and the retro-Michael reaction (Scheme 1). These observations have prompted us to conduct further research into this reaction for potential applications in the kinetic resolution of these adducts. In

• initially promotes deracemization by rapidly reacting with the enantiomer (3R,4S) of the diastereomer anti-1. Over time, the initial equilibrium is established either because the catalyst begins to react with the syn-diastereomer or because, once the retro-Michael reaction has occurred, the catalyst

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

• that might permit tuning of several consecutive catalytic steps [395], induced-fit binding, product release, allostery [396][397], or signaling. For the acyl transfer reaction, cage 1 is an inferior catalyst compared to cage 2, which we have postulated is due to the larger equilibrium cage height

The effect of neighbouring group participation and possible long range remote group participation in O-glycosylation

• Rituparna Das and
• Balaram Mukhopadhyay

Beilstein J. Org. Chem. 2025, 21, 369–406, doi:10.3762/bjoc.21.27

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

• in the weak field at 15.2–15.8 ppm for 7a,b and 14.3–14.8 ppm for 8a,b, respectively, as a broadened singlet peak. A dynamic equilibrium of tautomeric forms 7, 8 (OH)–7, 8 (NH) exists in solution, which can be detected by the broadening of the hydroxy group proton signal in the 1H NMR spectrum

• studied compounds. The difference in the energy characteristics of the (NH) and (OH) tautomeric forms of compounds 7a, 7b, 8a, and 8b in the polar solvent and the gas phase is small (2.0–3.8 kcal/mol), and probably the nature of the solvent can influence the shift of the equilibrium towards one of the

• large Stokes shift values (Table 2, Figure 5). This is consistent with the above conclusion about the existence of tautomeric equilibrium 7,8 (OH)–7,8 (NH) in solutions based on NMR data and DFT quantum chemical calculations (Scheme 2). The emission with a larger Stokes shift appears to correspond to

Red light excitation: illuminating photocatalysis in a new spectrum

• Lucas Fortier,
• Corentin Lefebvre and
• Norbert Hoffmann

Beilstein J. Org. Chem. 2025, 21, 296–326, doi:10.3762/bjoc.21.22

• therapeutic methods [78][79][80]. Such reactions can be performed at particular locations such as DNA or tubulin, when the photocatalyst is placed via a tethered ligand (Scheme 17) [81]. In the present case, the triarylmethine dye 67 was used as sensitizer. It is in equilibrium with the lactone form 68 and

Three-component reactions of conjugated dienes, CH acids and formaldehyde under diffusion mixing conditions

• Dmitry E. Shybanov,
• Maxim E. Kukushkin,
• Eugene V. Babaev,
• Nikolai V. Zyk and
• Elena K. Beloglazkina

Beilstein J. Org. Chem. 2025, 21, 262–269, doi:10.3762/bjoc.21.18

• 9 in toluene for 7 h led to the formation of an equilibrium mixture of these compounds in a ratio of ≈2:1 (Scheme 5). We propose that the reversible transformation of 8 to 9 proceeded via the intermediate formation of zwitterion 21, in which the charges were stabilized by mesomeric effects under

Heteroannulations of cyanoacetamide-based MCR scaffolds utilizing formamide

• Marios Zingiridis,
• Danae Papachristodoulou,
• Despoina Menegaki,
• Konstantinos G. Froudas and
• Constantinos G. Neochoritis

Beilstein J. Org. Chem. 2025, 21, 217–225, doi:10.3762/bjoc.21.13

• Goals (SDGs), wherein the 7th goal focuses on ensuring access to affordable, renewable and clean energy [1]. Moreover, the European Union has committed to ambitious environmental targets as part of the European Green Deal [2]. Advancements in C1 chemistry are pivotal to achieving this equilibrium. As

Nickel-catalyzed cross-coupling of 2-fluorobenzofurans with arylboronic acids via aromatic C–F bond activation

• Takeshi Fujita,
• Haruna Yabuki,
• Ryutaro Morioka,
• Kohei Fuchibe and
• Junji Ichikawa

Beilstein J. Org. Chem. 2025, 21, 146–154, doi:10.3762/bjoc.21.8

• findings suggest that nickelacyclopropanes E and 2-fluorobenzofurans 1 are in equilibrium (see Scheme 5). Consequently, in the absence of arylboronic acids 2, the consumption of 1 was suppressed. Upon adding phenylboronic acid (2a, 1.0 equiv) to the above reaction mixture, the coupling proceeded, producing

Direct trifluoroethylation of carbonyl sulfoxonium ylides using hypervalent iodine compounds

• Radell Echemendía,
• Carlee A. Montgomery,
• Fabio Cuzzucoli,
• Antonio C. B. Burtoloso and
• Graham K. Murphy

Beilstein J. Org. Chem. 2024, 20, 3182–3190, doi:10.3762/bjoc.20.263

• reductive elimination (path 1) [37][38][39]. This pathway initiates by formation of a halogen bond complex between 1a and the trifuoroethyl(mesityl)iodonium ion 2a’, where adduct XB-1 is presumably in equilibrium with isomeric XB-2. Reductive elimination of the iodoarene from XB-2 would furnish B, whose

• was found at a relative energy of 10.1 kcal/mol, where the C–I–C bond angle is 178° with C–I bond lengths of 2.2 Å (I–CH2CF3) and 2.9 Å. The reaction coordinate diagram for path 1 showed a near barrierless equilibrium between halogen bond adducts XB-1 and XB-2, where XB-2 has a C–I–C bond angle of 86

Tunable full-color dual-state (solution and solid) emission of push–pull molecules containing the 1-pyrindane moiety

• Anastasia I. Ershova,
• Sergey V. Fedoseev,
• Konstantin V. Lipin,
• Mikhail Yu. Ievlev,
• Oleg E. Nasakin and
• Oleg V. Ershov

Beilstein J. Org. Chem. 2024, 20, 3016–3025, doi:10.3762/bjoc.20.251

• group, a strong blue shift occurred down to 394 nm. The only exception was a solution of 1i in acetic acid, where two peaks were observed. Apparently, the weaker acetic acid caused just a partial protonation of the amino group, and the equilibrium shown in Scheme 2 was observed. This was evidenced by

• solutions of compounds 1a–i in toluene (top) and DMSO (bottom) taken under a 365 nm UV lamp. Normalized solid-state emission spectra of compounds 1a–i (bottom) and photos of powders taken under a 365 nm UV lamp (top). Synthesis of donor–acceptor 1-pyrindane derivatives 1. Plausible equilibrium of compounds