Substituent effects in N-acetylated phenylazopyrazole photoswitches

• Radek Tovtik,
• Dennis Marzin,
• Pia Weigel,
• Stefano Crespi and
• Nadja A. Simeth

Beilstein J. Org. Chem. 2025, 21, 830–838, doi:10.3762/bjoc.21.66

• substituent, tautomerism can become feasible and result in particularly fast relaxation rates. These results highlight the complex interplay between electronic effects and thermal isomerization pathways in this class of compounds. To summarize, this work provides a comprehensive understanding of how

• equipment, experimental procedures, compound characterization, UV–vis spectra at different concentrations, photochemical experiments, thermal isomerization analysis, and NMR spectra. Funding We thank the Swedish Vetenskapsrådet for a Starting Grant (2021-05414 to SC and to 2023-04088 to NAS). This work was

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

• reactions of 2-methylquinolines with 3,5-di-(tert-butyl)-1,2-benzoquinone [1] and benzophenones with o-chloranil [15]. The norcaradiene derivatives 5, formed in the next step by the intramolecular cyclization reaction of 4, undergo thermal isomerization into 2,3-dihydrotropolones 6. The formation of 2

Effect of substitution position of aryl groups on the thermal back reactivity of aza-diarylethene photoswitches and prediction by density functional theory

• Misato Suganuma,
• Daichi Kitagawa,
• Shota Hamatani and
• Seiya Kobatake

Beilstein J. Org. Chem. 2025, 21, 242–252, doi:10.3762/bjoc.21.16

• time scale [54]. Langton and co-workers demonstrated that the thermal isomerization rate of azobenzenes can be tuned over a time scale spanning 107 seconds by introducing appropriate chalcogens and halogens at the ortho-position of the benzene rings [55]. Thus, investigation of the strategies to

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

Photochromic derivatives of indigo: historical overview of development, challenges and applications

• Gökhan Kaplan,
• Zeynel Seferoğlu and
• Daria V. Berdnikova

Beilstein J. Org. Chem. 2024, 20, 228–242, doi:10.3762/bjoc.20.23

• Z-form. To prove this idea, in 1984, Omote and co-workers obtained intramolecularly bridged N,N'-azelaoylindigo (14a), N,N'-sebacoylindigo (14b), and intermolecularly bridged N',N''-sebacoylbis(N-acetylindigo) (15) and studied their Z–E thermal isomerization in comparison with N,N'-diacetylindigo

• + cations (500 equiv). At the same time, addition of TBA+ cations showed just a minimal impact on the stability of the Z-form comparable with the effect of counter anions and solvent polarity. In 2021, Tsubaki and co-workers synthesized bridged N,N′-dialkyl-substituted indigos 13 and studied their thermal

• isomerization and photochemical (only for 13a) isomerization [46]. Compounds 13 showed intrinsic planar chirality and their enantiomers could be separated by HPLC. Notably, upon thermal and photochemical isomerization of these compounds, no Z-isomers were detected and only the racemization took place. Such

Transition-metal-catalyzed domino reactions of strained bicyclic alkenes

• Austin Pounder,
• Eric Neufeld,
• Peter Myler and
• William Tam

Beilstein J. Org. Chem. 2023, 19, 487–540, doi:10.3762/bjoc.19.38

• undergoes a Claisen rearrangement to afford the endo-isomer 112. Thermal isomerization of 113a by a 6π-electrocyclic ring-opening/closing cascade leads to the to the final exo-isomer 107. In 2018, the Zhang lab investigated the Ru-catalyzed ring-opening/dehydration of oxabicyclic alkenes 30 via the C–H

Silica gel and microwave-promoted synthesis of dihydropyrrolizines and tetrahydroindolizines from enaminones

• Robin Klintworth,
• Garreth L. Morgans,
• Stefania M. Scalzullo,
• Charles B. de Koning,
• Willem A. L. van Otterlo and
• Joseph P. Michael

Beilstein J. Org. Chem. 2021, 17, 2543–2552, doi:10.3762/bjoc.17.170

• prior to acid-promoted cyclization cannot be ruled out, since conjugation in the push–pull system should weaken the C=C bond and lower its rotational barrier [20]. Similar enaminone isomerizations have been detected even at room temperature [48]. If thermal isomerization indeed takes place, then one

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

• bond opposite to the fluorine atom. A consequence of this is the tendency of fluorocyclopropanes, and in particular gem-difluorocyclopropanes, to undergo various transformations initiated by a homolytic C–C bond breaking. Thermal stereomutation: In 1975, Staricco and co-workers described the thermal

• isomerization of trans-1,2-dichloro-3,3-difluorocyclopropane (84) (Scheme 37) [82]. Further research in this area was performed by the groups of Jefford [83] and Dolbier [84], who studied the 1,1-difluoro-2,3-dimethylcyclopropanes 86 and 87 (Scheme 38). Dolbier found that geminal fluorine substituents lowered

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

Preparation of 2-phospholene oxides by the isomerization of 3-phospholene oxides

• Péter Bagi,
• Réka Herbay,
• Nikolett Péczka,
• Zoltán Mucsi,
• István Timári and
• György Keglevich

Beilstein J. Org. Chem. 2020, 16, 818–832, doi:10.3762/bjoc.16.75

• , reaching a final concentration of 1 and 4 (Figure 2a). The results of this kinetic study indicated that the electron-donating groups on the phenyl ring accelerated, while the electron-withdrawing groups decelerated the isomerization in the first few hours. All thermal isomerization processes lead to an

Photoreversible stretching of a BAPTA chelator marshalling Ca²⁺-binding in aqueous media

• Aurélien Ducrot,
• Arnaud Tron,
• Robin Bofinger,
• Ingrid Sanz Beguer,
• Jean-Luc Pozzo and
• Nathan D. McClenaghan

Beilstein J. Org. Chem. 2019, 15, 2801–2811, doi:10.3762/bjoc.15.273

• state (PSS) for the E→Z photoisomerization at 365 nm was 88:12 in favor of the cis-form (Figure 4). The reversibility of the photoswitching of the supramolecular host was tested over several isomerization cycles with little evidence of fatigue (Figure 5). Thermal isomerization Z→E resulted in the

A chiral self-sorting photoresponsive coordination cage based on overcrowded alkenes

• Constantin Stuckhardt,
• Diederik Roke,
• Wojciech Danowski,
• Edwin Otten,
• Sander J. Wezenberg and
• Ben L. Feringa

Beilstein J. Org. Chem. 2019, 15, 2767–2773, doi:10.3762/bjoc.15.268

• Pd2(stable Z-1)4; KB = 1758 ± 39 M−1 for Pd2(stable E-1)4 at 293 K). Finally, the photochemical and thermal isomerization behavior of the complexes was studied. Initially, the behavior of ligand 1 was studied by UV–vis and NMR spectroscopy, showing similar behavior as related first generation

A combinatorial approach to improving the performance of azoarene photoswitches

• Joaquin Calbo,
• Aditya R. Thawani,
• Rosina S. L. Gibson,
• Andrew J. P. White and
• Matthew J. Fuchter

Beilstein J. Org. Chem. 2019, 15, 2753–2764, doi:10.3762/bjoc.15.266

• (≈1000 days at 25 °C); one of the most stable azo photoswitches reported to date. We further extended the family of arylazopyrazoles with the help of theoretical modelling and discovered 3pzH to be near quantitatively (>98%) switched back and forth between isomers, with a long thermal isomerization half

Norbornadiene-functionalized triazatriangulenium and trioxatriangulenium platforms

• Roland Löw,
• Talina Rusch,
• Tobias Moje,
• Fynn Röhricht,
• Olaf M. Magnussen and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 1815–1821, doi:10.3762/bjoc.15.175

• ; quadricyclane; self-assembled monolayers; TATA platform; thermal isomerization; TOTA platform; Introduction Recently, we discovered that the thermochemically forbidden cis–trans isomerization of azobenzenes can be efficiently catalysed by a very peculiar mechanism on bulk gold [1]. In heterogeneous catalysis

• thermal isomerization of QC 1b back to NBD 1a was investigated by 1H NMR measurements (Figure 4). The cycloreversion follows a first order reaction, the rate constant could be determined by logarithmic fitting of the integrals of the CH2 signals next to the nitrogen atoms of the platform as k = 1.06·10−3

• 1a and 1b after 2 h irradiation with 311 nm under nitrogen atmosphere (28% 1a/72% 1b). Determination of the thermal isomerization rate k of 1b (QC) by 1H NMR spectroscopy (toluene, 293.5 K, 800 μmol/L, under nitrogen). ΔY: ln {[QC]t/[QC]0}, [QC]t: 1H NMR integral of the CH2 group neighbouring the N

Diazocine-functionalized TATA platforms

• Roland Löw,
• Talina Rusch,
• Fynn Röhricht,
• Olaf Magnussen and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 1485–1490, doi:10.3762/bjoc.15.150

• ). All energies are given in kcal mol−1. Photostationary states (PSS) of para-diazocine-TATA 1 (2.05 mmol/L) and meta-diazocine-TATA 2 (2.27 mmol/L) upon irradiation with light of 405 nm, 525 nm and thermal isomerization half-life (t1/2) determined with 1H NMR spectroscopy (in deuterated toluene). The

Precious metal-free molecular machines for solar thermal energy storage

• Meglena I. Kandinska,
• Snejana M. Kitova,
• Vladimira S. Videva,
• Stanimir S. Stoyanov,
• Stanislava B. Yordanova,
• Stanislav B. Baluschev,
• Silvia E. Angelova and
• Aleksey A. Vasilev

Beilstein J. Org. Chem. 2019, 15, 1096–1106, doi:10.3762/bjoc.15.106

• which was found to be long enough to reach a photostationary state. The kinetics of the cis–trans thermal isomerization were studied by measuring the absorbance at a fixed wavelength in the dark as a function of time after irradiation stopped until the initial absorbance value before excitation was

Synthesis and selected transformations of 2-unsubstituted 1-(adamantyloxy)imidazole 3-oxides: straightforward access to non-symmetric 1,3-dialkoxyimidazolium salts

• Grzegorz Mlostoń,
• Małgorzata Celeda,
• Katarzyna Urbaniak,
• Marcin Jasiński,
• Vladyslav Bakhonsky,
• Peter R. Schreiner and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2019, 15, 497–505, doi:10.3762/bjoc.15.43

• ppm belongs to HN(3). The 13C NMR spectrum confirmed the structure of 9 by the signal of the C(2)=O group found at 153.0 ppm. The corresponding band in the IR spectrum appeared at 1702 cm−1as the strongest absorption. Thermal isomerization of 7b was also tested. However, boiling in bromobenzene for 15

• new group of 1-(adamantyloxy)imidazole-2-thiones, which potentially are of interest for medicinal chemistry. The acetic acid anhydride assisted isomerization reaction of a new N-oxide leads to the corresponding imidazol-2-one. However, the attempted thermal isomerization of a 1-(adamantyloxy)imidazole

London dispersion as important factor for the stabilization of (Z)-azobenzenes in the presence of hydrogen bonding

• Andreas H. Heindl,
• Raffael C. Wende and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2018, 14, 1238–1243, doi:10.3762/bjoc.14.106

• Discussion To further investigate the prior observations, the thermal Z→E isomerization rates of azobenzenes 4–7 were determined by UV–vis spectroscopy in several solvents at 25 °C and 35 °C, respectively. The lowest thermal isomerization rates were found for the crowded 4,4’-bis[4-(3,5,5

The photodecarboxylative addition of carboxylates to phthalimides as a key-step in the synthesis of biologically active 3-arylmethylene-2,3-dihydro-1H-isoindolin-1-ones

• Ommid Anamimoghadam,
• Saira Mumtaz,
• Anke Nietsch,
• Gaetano Saya,
• Cherie A. Motti,
• Jun Wang,
• Peter C. Junk,
• Ashfaq Mahmood Qureshi and
• Michael Oelgemöller

Beilstein J. Org. Chem. 2017, 13, 2833–2841, doi:10.3762/bjoc.13.275

• acetone/water [34][59]. The high stereoselectivity during the formation of compounds 7a–q is supported by the higher stability of the E-isomer, as shown for other simple N-substituted benzylideneisoindolin-1-ones [12][21]. Remarkably, acidic reaction conditions induced thermal isomerization of compounds

• 8a–y, possibly via an acylaminium cation intermediate (Scheme 9) [60]. The change in stability may be caused by a stabilizing ionic–π interaction for the Z-isomer during isomerization [61]. A similar thermal isomerization towards the more stable isomer induced by catalytic amounts of pyridinium p

Are boat transition states likely to occur in Cope rearrangements? A DFT study of the biogenesis of germacranes

• José Enrique Barquera-Lozada and
• Gabriel Cuevas

Beilstein J. Org. Chem. 2017, 13, 1969–1976, doi:10.3762/bjoc.13.192

• the Cope rearrangement can proceed, the (Z,E)-germacranolide 1, must isomerize to the corresponding (E,E)-germacranolide 4. This process is highly unfavorable, its energetic barrier is about 55.7 kcal/mol, which is very close to the reported activation energies for the ethylene thermal isomerization

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

• 292, which underwent thermal isomerization to give the reactive intermediate 293 [114]. As a result of the Diels–Alder reaction of the latter with cyclopentenone 239, the adduct 294 was formed, which was further subjected to the TEA-induced cleavage at 100 °C to give the desired 1-indanone 295 (Scheme

Diels–Alder reactions of myrcene using intensified continuous-flow reactors

• Christian H. Hornung,
• Miguel Á. Álvarez-Diéguez,
• Thomas M. Kohl and
• John Tsanaktsidis

Beilstein J. Org. Chem. 2017, 13, 120–126, doi:10.3762/bjoc.13.15

• thermal isomerization at temperatures between 400 and 600 °C. This was first described by Goldblatt and Palkin in 1947 [11]. Myrcene is a very versatile molecule that can act as the starting material for several valuable compounds. The industrial production of a series of top-selling flavors and

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

Thermodynamically stable [4 + 2] cycloadducts of lanthanum-encapsulated endohedral metallofullerenes

• Yuta Takano,
• Yuki Nagashima,
• M. Ángeles Herranz,
• Nazario Martín and
• Takeshi Akasaka

Beilstein J. Org. Chem. 2014, 10, 714–721, doi:10.3762/bjoc.10.65

• 4a was heated to a temperature of 250 °C, selective decomposition of 3a was observed (Figure 6). Since the peak of pristine La@C82 at ca. 30 min is observed after heating (see Figure 6b), most probably the detachment of the addend is taking place and a thermal isomerization thereafter. After HPLC

Cyclization of substitued 2-(2-fluorophenylazo)azines to azino[1,2-c]benzo[d][1,2,4]triazinium derivatives

• Aleksandra Jankowiak,
• Emilia Obijalska and
• Piotr Kaszynski

Beilstein J. Org. Chem. 2013, 9, 1873–1880, doi:10.3762/bjoc.9.219

• -isomers cannot be populated thermally due to the high E → Z thermal isomerization barrier (ΔG‡298 > 35 kcal/mol) [7]. The Z-forms however, thermally and also photochemically isomerize back to the more stable E-isomers, and the rates are substituent depended [12]. Thus, with the broadband irradiation a