Synthesis of N-acetyl diazocine derivatives via cross-coupling reaction

• Thomas Brandt,
• Pascal Lentes,
• Jeremy Rudtke,
• Michael Hösgen,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2025, 21, 490–499, doi:10.3762/bjoc.21.36

• Abstract Diazocines are photoswitches derived from azobenzenes by bridging the two phenyl rings in ortho position with a CH2CH2 group forming an eight membered (diazocine) ring. Diazocine is superior to most azobenzenes in almost all photophysical properties (switching efficiency, quantum yield

• azobenzenes, spiropyranes and diarylethenes in organic solvents [3][13][15]. There are two strategies of applying diazocines in photopharmacology. The first one exploits the structural similarity of the tricyclic diazocine framework to the tricyclic structure of, e.g., tetrahydrodibenzazocines [16][17] and

• examples of last-step modifications of azobenzenes via Suzuki–Miyaura reactions in the current literature, which indicate that the reaction conditions are compatible with azo groups [27][28]. Suzuki–Miyaura reaction of 2 and 3 with different phenylboronic acids resulted in the formation of the

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

• -withdrawing substituents on the N-aryl moieties enhanced the thermal stability of the Z-isomers while maintaining the advantageous photoswitching properties upon irradiation with red light [52]. The effect of substituents on the thermal cis–trans isomerization of azobenzenes has also been widely studied, and

• 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

Extension of the π-system of monoaryl-substituted norbornadienes with acetylene bridges: influence on the photochemical conversion and storage of light energy

• Robin Schulte,
• Dustin Schade,
• Thomas Paululat,
• Till J. B. Zähringer,
• Christoph Kerzig and
• Heiko Ihmels

Beilstein J. Org. Chem. 2024, 20, 3061–3068, doi:10.3762/bjoc.20.254

• ], azobenzenes [16][17][18][19], dihydroazulenes [20][21], or azaborines [22][23]. However, the most prominent feasible MOST system is the [2 + 2] photocycloaddition–cycloreversion cycle between norbornadiene (1a) and quadricyclane (2a), which has several advantageous properties (Scheme 1) [8][14][24]. In

Supramolecular assemblies of amphiphilic donor–acceptor Stenhouse adducts as macroscopic soft scaffolds

• Ka-Lung Hung,
• Leong-Hung Cheung,
• Yikun Ren,
• Ming-Hin Chau,
• Yan-Yi Lam,
• Takashi Kajitani and
• Franco King-Chi Leung

Beilstein J. Org. Chem. 2024, 20, 1590–1603, doi:10.3762/bjoc.20.142

• -driven supramolecular assemblies on a microscopic length scale, such as those containing spiropyrans, azobenzenes, and indigos, have been used in transformations in aqueous medium [35][45][46]. However, very few examples of visible-light-driven supramolecular transformation on a macroscopic length scale

Photoswitchable glycoligands targeting Pseudomonas aeruginosa LecA

• Yu Fan,
• Ahmed El Rhaz,
• Stéphane Maisonneuve,
• Emilie Gillon,
• Maha Fatthalla,
• Franck Le Bideau,
• Guillaume Laurent,
• Samir Messaoudi,
• Anne Imberty and
• Juan Xie

Beilstein J. Org. Chem. 2024, 20, 1486–1496, doi:10.3762/bjoc.20.132

• photoswitchable tools, few photochromic lectin ligands have been developed. We have designed and synthesized several O- and S-galactosyl azobenzenes as photoswitchable ligands of LecA and evaluated their binding affinity with isothermal titration calorimetry. We show that the synthesized monovalent glycoligands

• due to stronger unfavorable entropy, they are in general of lower affinity. The validation of this proof-of-concept and the dissection of thermodynamics of binding will help for the further development of lectin ligands that can be controlled by light. Keywords: carbohydrates; glycosyl azobenzenes

• [11][12][13][14][15][16][17][18]. The group of Lindhorst has reported a series of mannosyl azobenzenes targeting E. coli lectin FimH, demonstrating the possibility to control the type 1 fimbriae-mediated bacterial adhesion to a self-assembled monolayer of mannosyl azobenzene on a gold surface [19][20

Generation of alkyl and acyl radicals by visible-light photoredox catalysis: direct activation of C–O bonds in organic transformations

• Mithu Roy,
• Bitan Sardar,
• Itu Mallick and
• Dipankar Srimani

Beilstein J. Org. Chem. 2024, 20, 1348–1375, doi:10.3762/bjoc.20.119

• hydroacylation of azobenzenes employing acids as hydroacylating reagents (Scheme 4). The reaction progressed smoothly, involving the cleavage of the C–O bond using a photogenerated phosphoranyl radical. The methodology demonstrated an excellent compatibility with a wide range of azobenzenes and carboxylic acids

• azobenzenes with carboxylic acids. Photoredox-catalyzed synthesis of flavonoids. Synthesis of O-thiocarbamates and photocatalytic reduction of O-thiocarbamates. Deoxygenative borylation of alcohols. Trifluoromethylation of O-alkyl thiocarbonyl substrates. Redox-neutral radical coupling reactions of alkyl

Novel route to enhance the thermo-optical performance of bicyclic diene photoswitches for solar thermal batteries

• Akanksha Ashok Sangolkar,
• Rama Krishna Kadiyam and
• Ravinder Pawar

Beilstein J. Org. Chem. 2024, 20, 1053–1068, doi:10.3762/bjoc.20.93

• /vinylheptafulvene, azobenzenes, tetracarbonyl(fulvalene)diruthenium complexes, norbornadiene/quadricyclane (NBD/QC), anthracenes, etc. exhibit a few promising properties for MOST applications [10][12][13]. However, these photoswitching couples still lack one or more important properties required in MOST systems and

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

Dissecting Mechanochemistry III

• Lars Borchardt and
• José G. Hernández

Beilstein J. Org. Chem. 2022, 18, 1454–1456, doi:10.3762/bjoc.18.150

• were also key reagents to develop the mechanochemical halogenation of azobenzenes as studied by Ćurić and co-workers [4]. They demonstrated how, depending on the azobenzene structure, the halogenation of the C–H bonds with NBX occurred in the presence of Pd(II) catalysts or under metal-free conditions

• José G. Hernández Bochum, Medellín, October 2022 ORCID® iDs Lars Borchardt - https://orcid.org/0000-0002-8778-7816 José G. Hernández - https://orcid.org/0000-0001-9064-4456 a) Mechanochemical PEG-400-assisted halogenation of phenols and anilines using NXS. b) Halogenation of azobenzenes with NXS

Continuous flow synthesis of azobenzenes via Baeyer–Mills reaction

• Jan H. Griwatz,
• Anne Kunz and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2022, 18, 781–787, doi:10.3762/bjoc.18.78

• Azobenzene, as one of the most prominent molecular switches, is featured in many applications ranging from photopharmacology to information or energy storage. In order to easily and reproducibly synthesize non-symmetric substituted azobenzenes in an efficient way, especially on a large scale, the commonly

• . Keywords: azobenzenes; Baeyer–Mills reaction; continuous flow; molecular switches; solar fuel; Introduction Although the red-colored azobenzenes (AB) have been known for years as dyes, their applications nowadays span from energy and information storage [1][2][3][4][5], organocatalysis [6], photobiology

• reliable synthesis of symmetric ABs in high yields via a Cu-catalyzed oxidative coupling of aniline derivatives [17]. This synthesis can be also used for the formation of non-symmetric AB, however, only for a selected set of anilines. One of the most applied methods to access non-symmetric azobenzenes is

Mechanochemical halogenation of unsymmetrically substituted azobenzenes

• Dajana Barišić,
• Mario Pajić,
• Ivan Halasz,
• Darko Babić and
• Manda Ćurić

Beilstein J. Org. Chem. 2022, 18, 680–687, doi:10.3762/bjoc.18.69

• Dajana Barisic Mario Pajic Ivan Halasz Darko Babic Manda Curic Division of Physical Chemistry, Ruđer Bošković Institute, Bijenička cesta 54, Zagreb, Croatia 10.3762/bjoc.18.69 Abstract The direct and selective mechanochemical halogenation of C–H bonds in unsymmetrically substituted azobenzenes

• proceeds by electrophilic cleavage with neutral NBS or the hydrogen bond complex NBS∙∙∙TsOH as a bromine source. Here we present the mechanochemical selective halogenation of unsymmetrically substituted azobenzenes by NXS (X = Cl, Br, or I). The liquid-assisted grinding of para-halogenated derivatives of

• azobenzene with NXS and Pd(OAc)2 as precatalyst in the presence of TsOH and MeCN as solid and liquid additives, respectively, led to the ortho-halogenated products relative to the azo group of the azobenzenes. In situ Raman monitoring of these reactions confirmed that the most favorable reaction pathway is

Recent advances in the asymmetric phosphoric acid-catalyzed synthesis of axially chiral compounds

• Alemayehu Gashaw Woldegiorgis and
• Xufeng Lin

Beilstein J. Org. Chem. 2021, 17, 2729–2764, doi:10.3762/bjoc.17.185

• the reaction of 2-substituted indoles with azobenzenes proceeded smoothly in the presence of the chiral phosphoric acid catalyst (R)-CPA 9. At a catalyst loading of 0.2 mol %, the intermediate I-5 was simultaneously cyclized to I-6, followed by β-H elimination and chirality transfer to afford another

On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

• Renato L. Carvalho,
• Amanda S. de Miranda,
• Mateus P. Nunes,
• Roberto S. Gomes,
• Guilherme A. M. Jardim and
• Eufrânio N. da Silva Júnior

Beilstein J. Org. Chem. 2021, 17, 1849–1938, doi:10.3762/bjoc.17.126

• organometallic chemistry and catalysis [128]. The first example of a stoichiometric manganese-mediated C–H activation, reported by Stone, Bruce, and co-workers (1970) [129], was an ortho-metalation in azobenzenes. In recent years, with the expansion of the C–H activation field, manganese catalysts have been

Sustainable manganese catalysis for late-stage C–H functionalization of bioactive structural motifs

• Jongwoo Son

Beilstein J. Org. Chem. 2021, 17, 1733–1751, doi:10.3762/bjoc.17.122

• azobenzenes was unveiled [1], manganese catalysts have exhibited a significant capacity for powerful C–H functionalization, and they have therefore been actively utilized in the area of sustainable organic syntheses [2][3][4][5][6]. Catalytic late-stage C–H functionalization, a highly efficient synthetic

Substituted nitrogen-bridged diazocines

• Pascal Lentes,
• Jeremy Rudtke,
• Thomas Griebenow and
• Rainer Herges

Beilstein J. Org. Chem. 2021, 17, 1503–1508, doi:10.3762/bjoc.17.107

• Diazocines (bridged azobenzenes) are frequently used photoswitches with outstanding photophysical properties. Parent diazocine (CH2–CH2-bridged) exhibits well-separated n–π* transitions, which allow excellent photoconversion between the Z and E configurations ((Z→E)385 nm = 92%, (E→Z)525 nm > 99% in n-hexane

• ) with light in the visible region [1]. Moreover, the Z-boat configuration is the thermodynamically stable isomer [2][3][4][5][6][7][8][9]. The latter property (i.e., the inverted stability compared to azobenzenes) makes them promising candidates for applications in photopharmacology. In the majority of

• azobenzene-based photopharmacophores, the bent Z configuration is biologically inactive [10][11][12]. Hence, (and in contrast to azobenzenes) the thermodynamically stable and biologically inactive Z-isomer can be administered and switched on with light at the site of interest with spatiotemporal resolution

Azo-dimethylaminopyridine-functionalized Ni(II)-porphyrin as a photoswitchable nucleophilic catalyst

• Jannis Ludwig,
• Julian Helberg,
• Hendrik Zipse and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2119–2126, doi:10.3762/bjoc.16.179

• following several approaches using a variety of photochromic systems. Feringa et al. recently published a review including systems based on double bond isomerizations [1]. An earlier review from the same group summarized light and redox responsive catalytic systems including azobenzenes, diarylethenes

• of the background reaction without catalyst is low, and the influence of the solvent on the reaction rate is small [10][32]. No catalytic effect for the N=N functional group of azobenzenes was previously observed in similar systems [10]. Ni-porphyrin Ni-TPPF20 8 (without azopyridine substitution

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

Potent hemithioindigo-based antimitotics photocontrol the microtubule cytoskeleton in cellulo

• Alexander Sailer,
• Franziska Ermer,
• Yvonne Kraus,
• Rebekkah Bingham,
• Ferdinand H. Lutter,
• Julia Ahlfeld and
• Oliver Thorn-Seshold

Beilstein J. Org. Chem. 2020, 16, 125–134, doi:10.3762/bjoc.16.14

• -hydroxyhemistilbene motif, a structural feature which is denied to most azobenzenes due to the negligibly short lifetimes of their metastable Z-isomers, which proved crucial to enhancing the potency and photoswitchability. The HITubs were ten times more potent than previously reported hemithioindigo

• differential potency between isomers of the resulting photopharmaceutical, than peripheral attachment (referred to as azo-extension in the case of azobenzenes [18]). We therefore desired to maintain the embedding strategy, yet to improve potency we chose to break with substitution patterns strictly based on

• azobenzenes or styrylbenzothiazoles) is desirable, in particular for cell-free mechanistic studies [33]. More broadly, this work also shows that the HTI scaffold robustly enables the photoswitchable use of resonance-capable substituents that can establish high-affinity interactions (such as para-hydroxy

Photocontrolled DNA minor groove interactions of imidazole/pyrrole polyamides

• Sabrina Müller,
• Jannik Paulus,
• Jochen Mattay,
• Heiko Ihmels,
• Veronica I. Dodero and
• Norbert Sewald

Beilstein J. Org. Chem. 2020, 16, 60–70, doi:10.3762/bjoc.16.8

• -33501 Bielefeld, Germany Organic Chemistry II, Department Chemistry – Biology, Siegen University, Adolf-Reichwein-Str. 2, D-57068 Siegen, Germany 10.3762/bjoc.16.8 Abstract Azobenzenes are photoswitchable molecules capable of generating significant structural changes upon E-to-Z photoisomerization in

• substance, once located at the DNA target, with an external stimulus. Azobenzenes are photoswitchable molecules capable of generating significant structural changes in peptides or small molecules, thereby controlling their geometry and functionality upon irradiation [10][11][12][13]. While isomerization of

• ]. According to molecular dynamics calculations, the 3,3'-substituted azobenzenes are more suitable as photoswitchable building blocks to induce a hairpin motif than the 4,4'-substituted correlates [35]. For 3,3'-substituted azobenzenes, the Z-form is expected to display higher thermal stability than for the

Starazo triple switches – synthesis of unsymmetrical 1,3,5-tris(arylazo)benzenes

• Andreas H. Heindl and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2020, 16, 22–31, doi:10.3762/bjoc.16.4

• ; Introduction The reversible photochemically induced structural change of azobenzenes (ABs) opens various ways towards systems manipulations on the molecular level [1][2]. Upon irradiation with UV light (ca. 350 nm), the thermodynamically more stable (E)-AB isomerizes to the higher-energy Z-isomer [3]. The

Synthesis and characterization of bis(4-amino-2-bromo-6-methoxy)azobenzene derivatives

• David Martínez-López,
• Amirhossein Babalhavaeji,
• Diego Sampedro and
• G. Andrew Woolley

Beilstein J. Org. Chem. 2019, 15, 3000–3008, doi:10.3762/bjoc.15.296

• azobenzenes – have recently been found to exhibit photoswitching properties suitable for in vivo use [8][9][10]. Typically, the formation of azonium ions from aminoazobenzenes occurs at pH < 3.5 [11][12], however, the pKa of the trans-azonium ion 1 is ca. 7.5 in aqueous solution (Figure 1) [9][10]. The

• substituent in an attempt to enhance water solubility. Late-stage functionalization of the ortho-position was carried out through a palladium(II)-catalyzed C–H activation, resulting in ortho-brominated azobenzenes [21]. Photochemical characterization Despite the morpholino substituent, compound 4 was found to

• , which showed half-lives ranging from 50 ms [25] to a few seconds [26][27]. Instead, compounds 4 and 5 exhibited photoswitching properties similar to those reported for tetra-ortho-thiol-substituted azobenzenes [17]. Conclusion Substitution of p-aminoazobenzene with ortho-bromo and ortho-methoxy groups

Chemical tuning of photoswitchable azobenzenes: a photopharmacological case study using nicotinic transmission

• Lorenzo Sansalone,
• Jun Zhao,
• Matthew T. Richers and
• Graham C. R. Ellis-Davies

Beilstein J. Org. Chem. 2019, 15, 2812–2821, doi:10.3762/bjoc.15.274

• . Keywords: acetylcholine receptors; bidirectional; photoswitchable drug; tetrafluoroazobenzene; visible light; Introduction Starting in 1937, azobenzenes (ABs) have attracted much attention because they undergo a photoreversible chemical transformation of the thermodynamically favored trans configuration

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

• differences between them, which may have consequences on the chelation, energy-minimized (PM6) structures were determined (Figure 2). The trans-form was found to be the lowest energy structure, as is generally observed for azobenzenes [37]. In the trans- versus cis-chelates the following bond lengths were

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

• supramolecular palladium complexes caused immediate crystallization [22]. Moreover, azobenzenes have been used to functionalize both the interior [23] and exterior [24] of SCCs to photochemically control guest binding and release. Furthermore, incorporation of dithienylethene into the ligands connecting the

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

• results therefore define improved designs for high performance azo switches, which will allow for high precision optically addressable applications using such components. Keywords: arylazopyrazoles; azobenzenes; molecular switches; ortho-substitution; photoswitches; thermal half-life; Introduction

• ] is accompanied by large variations in their absorption spectra. However, azobenzenes remain one of the most popular photoswitches owing to their stability, reliability and tunability: azobenzenes provide high extinction coefficients and quantum yields, allowing switching between Z- and E-isomers with

• thermal stability of the Z-isomer. Despite the huge body of structure–property relationship studies known for substituted azobenzenes [8][9], it is still common to observe azo photoswitches that undergo incomplete photoswitching and/or possess low Z-isomer thermal stability. Perhaps the most important