Stereoselective electrochemical intramolecular imino-pinacol reaction: a straightforward entry to enantiopure piperazines

• Margherita Gazzotti,
• Fabrizio Medici,
• Valerio Chiroli,
• Laura Raimondi,
• Sergio Rossi and
• Maurizio Benaglia

Beilstein J. Org. Chem. 2025, 21, 1897–1908, doi:10.3762/bjoc.21.147

• photochemical and electrochemical methods, have been explored. Over the past two decades a variety of light-promoted imino-pinacol coupling reactions have been developed, involving the use of catalytic transition-metal complexes [35][36], organic dyes [37][38][39], and polyaromatic compounds [40][41] as

Continuous-flow-enabled intensification in nitration processes: a review of technological developments and practical applications over the past decade

• Feng Zhou,
• Chuansong Duanmu,
• Yanxing Li,
• Jin Li,
• Haiqing Xu,
• Pan Wang and
• Kai Zhu

Beilstein J. Org. Chem. 2025, 21, 1678–1699, doi:10.3762/bjoc.21.132

• dramatically, and the number of nitrogen-containing compounds continuously increased. These compounds find broad applications in synthesizing energetic materials, dyes, flavorings and fragrances, pharmaceutical and pesticide intermediates, as well as specialty chemicals [2]. As delineated in Figure 1, a

• . In contrast, bulk chemical industries including agrochemicals, dyes, and fine chemicals often operate at thousands to tens of thousands of tons annually. Nevertheless, many successful applications of flow-chemistry technology, emerged as a pivotal approach in industrial nitration processes, focused

Catalytic asymmetric reactions of isocyanides for constructing non-central chirality

• Jia-Yu Liao

Beilstein J. Org. Chem. 2025, 21, 1648–1660, doi:10.3762/bjoc.21.129

• of structurally novel atropisomeric N-arylindoles 56 bearing an eight-membered lactam in 51–85% yield with 54–92% ee. Of note, these scaffolds exhibited remarkably large Stokes shifts, showing great potential in the development of fluorescent dyes. Desymmetrization of prochiral compounds Beyond DKR

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

• conjugated systems, enabling the design of donor–acceptor helicenes with tunable photophysical properties. In 2020, Ema and co-workers developed a series of chiral carbazole-based BODIPY analogues 35a–f, derived from helical carbazole-based BF2 dyes [49] (Table 11). These analogues exhibit red-shifted

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

• , Bulgaria Department of Chemistry, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark 10.3762/bjoc.21.105 Abstract Tautomerism in two new azo dyes, based on 7-hydroxyquinoline, has been considered from the viewpoint of the proton crane concept. Although 8-(phenyldiazenyl)quinolin-7-ol exists in

• 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

• number of industrially used azo dyes [1][3] and therefore its tautomerism is studied in details. The existing experimental data for low polar solvents (cyclohexane and tetrachloromethane) indicate a ΔG value of around 0.4 kcal/mol [53] at room temperature, which gives a prevalence of the E-tautomer (a

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

• ], and dyes [15][16] serve as promising structures for constructing and designing novel PCs. These structures show a high electron affinity, stability, and the possibility of tuning their physicochemical properties by substituting the two aromatic rings. In 2018, Sang Kwon and co-workers reported a

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

• have been described and extensively studied [1][2]. Among these, azobenzenes belong to the most common ones [3]. They were firstly explored almost 200 years ago [4] and initially used mainly as dyes or pigments [5]. Relatively recently, azobenzenes started to become an important part of state-of-the

• mechanism is one of the fastest relaxation mechanism for heterocyclic azobenzenes (typically for most of the azo dyes [45]). However, the nature of the mechanism is still a matter of current debate, and additional factors, such as the presence of tautomerizable groups [46][47], and the involvement of the

Synthesis of HBC fluorophores with an electrophilic handle for covalent attachment to Pepper RNA

• Raphael Bereiter and
• Ronald Micura

Beilstein J. Org. Chem. 2025, 21, 727–735, doi:10.3762/bjoc.21.56

• and the new ones) for covalent attachment to the Pepper aptamer in vitro. Results and Discussion Background The fluorescent light-up aptamer Pepper binds a series of structurally related synthetic dyes that contain a stilbene core. The lead compound is (4-((2-hydroxyethyl)(methyl)amino)benzylidene

• have shown that this feature can be exploited to construct a covalent bond between the fluorophore and the RNA by replacing the N-hydroxyethyl group of the dye with an electrophilic handle, resulting in efficient RNA alkylation at the N7 of G41 [11]. Synthesis and evaluation of Pepper dyes with an

• reacted with 4-cyanophenylacetonitrile to give compound 10, followed by installing the bromobutyl handle with 4-bromobutanol under Mitsunobu conditions (Scheme 3). Next, HBC dyes 7, 8, 9, and 11 were tested for their reactivity with the Pepper aptamer. They were incubated together with the RNA in buffer

Unprecedented visible light-initiated topochemical [2 + 2] cycloaddition in a functionalized bimane dye

• Metodej Dvoracek,
• Brendan Twamley,
• Mathias O. Senge and
• Mikhail A. Filatov

Beilstein J. Org. Chem. 2025, 21, 500–509, doi:10.3762/bjoc.21.37

• conventions. Although these dyes have been known since 1978, their photochemistry has only been briefly explored. In this work, during the synthesis of a series of these dyes (Figure 2a), we observed an unprecedented intermolecular [2 + 2] cycloaddition of syn-(ethoxycarbonyl,chloro)bimane (Cl2B), seen in

• . Conclusion Following the observation of the topochemical cycloaddition of Cl2B, two other bimane dyes, Me2B and Me4B, were synthesized and investigated for their ability to undergo this reaction when initiated by visible light. A notable feature of this reaction is that it occurs only in the solid state, not

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

• have been extensively studied in the literature such as bridged Eosin Y 37 [44], BODIPY 38 [45], and dibenzothiazole 39 (Figure 5) [46]. Indeed, organic dyes, with their inherent advantages of low toxicity, environmental friendliness, and tunable optical properties, represent a promising alternative

• processes. Cyanins have been shown to effectively initiate radical polymerization under visible light through mechanisms such as borate oxidation [61] and 1,3,5-triazine reduction [62]. More recently, cyanin dyes have enabled the reduction of iodonium salts under NIR excitation [63][64]. These preliminary

• , Goddard et al. have developed a second generation of cyanin dyes. For example, in the case of the photocatalyzed trifluoromethylation of alkenes, it has been shown that the stability of the photocatalyst was crucial for achieving efficient and faster conversion. In their study, the authors have reported

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

• of the axle ends (Figure 11B, bottom). Furthermore, [3]rotaxanes bearing spacer moieties were synthesized as the model compounds of the macromolecular [3]rotaxane. In these [3]rotaxanes, Cotton effects were only observed on the dyes near the central CD units, and the aromatic groups located far from

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

• unchanged. This represents a rare approach for the design of such fluorophores. Arylidene derivatives of pyrindane were found to be efficient fluorescent dyes showing a moderate to high emission quantum yield. The push–pull molecules were also characterized by a dual-state emission (in solution and in the

Advances in radical peroxidation with hydroperoxides

• Oleg V. Bityukov,
• Pavel Yu. Serdyuchenko,
• Andrey S. Kirillov,
• Gennady I. Nikishin,
• Vera A. Vil’ and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2024, 20, 2959–3006, doi:10.3762/bjoc.20.249

The charge transport properties of dicyanomethylene-functionalised violanthrone derivatives

• Sondos A. J. Almahmoud,
• Joseph Cameron,
• Dylan Wilkinson,
• Michele Cariello,
• Claire Wilson,
• Alan A. Wiles,
• Peter J. Skabara and
• Graeme Cooke

Beilstein J. Org. Chem. 2024, 20, 2921–2930, doi:10.3762/bjoc.20.244

• frontier orbitals. Electrochemical studies The electrochemical properties of the dyes were investigated by square wave voltammetry (SWV) and cyclic voltammetry (CV) and the data are summarised in Table 1, with the plots shown in Figure 6. All the materials exhibit at least one reversible reduction and two

• reversible oxidation waves as shown from the CV data (Figure 6 and Table 1). This reversibility is crucial for the regeneration of dyes following redox processes. The compounds display ionisation energies (IEs) of −5.38 eV, −5.34 eV, and −5.40 eV for 3a, 3b, and 3c, respectively, with electron affinities

N-Glycosides of indigo, indirubin, and isoindigo: blue, red, and yellow sugars and their cancerostatic activity

• Peter Langer

Beilstein J. Org. Chem. 2024, 20, 2840–2869, doi:10.3762/bjoc.20.240

• readily available and cheap. Since then, indigo was produced in large scale. The synthesis, derivatization, and application of indigo derivatives have been widely studied [1][2][3]. Besides their application as dyes, indigo derivatives represent versatile tools for the development of innovative

• malignant cutaneous melanoma cells HT-144 (ATCC HTB-63) and lung carcinoma (H157) cell line (ATCC CRL-5802). Conclusion Since the 1990s, we are witnessing a renaissance of the chemistry of the old pigment dyes indigo, indirubin, and isoindigo, due to their anticancer activity which dates back to early

Applications of microscopy and small angle scattering techniques for the characterisation of supramolecular gels

• Connor R. M. MacDonald and
• Emily R. Draper

Beilstein J. Org. Chem. 2024, 20, 2608–2634, doi:10.3762/bjoc.20.220

• , meaning no drying is required of the material, the material itself needs to be fluorescent (but not quenching upon assembly) or the addition of a dye is required. Such dyes need to be able to stick with the fibres, rather than sitting in the pores. Therefore, the fluorescent material is either chemically

• attached to the molecules themselves or is interacting with them. Introducing fluorescent dyes to self-assembling systems affects their chemical and mechanical stability as the hydrophobic features can destabilise the self-assembled network [18]. This reliance on fluorescence labels or dyes leading to a

• use of fluorescence probes should be used in tandem with CLSM. For example, Raeburn et al. showed that the addition of molecular rotors and fluorescent dyes affects the bulk network of self-assembled materials using rheology. The co-packing was observed to alter rheological properties of the materials

Anion-dependent ion-pairing assemblies of triazatriangulenium cation that interferes with stacking structures

• Yohei Haketa,
• Takuma Matsuda and
• Hiromitsu Maeda

Beilstein J. Org. Chem. 2024, 20, 2567–2576, doi:10.3762/bjoc.20.215

• been widely investigated in the past decades for application as fluorescent dyes [3][4][5], chirality inducers [6][7][8], acceptors for photoinduced electron transfer (PET) [9][10], and components of supramolecular assemblies [11][12][13][14]. Owing to the stable π-electronic systems showing unique

• +) cations, used as visible light fluorescent dyes, have been synthesized via a nucleophilic aromatic substitution (SNAr) reaction with primary alkylamines (e.g., 1a+; Figure 1) [15][16]. The highly planar geometry of the TATA+ core unit induces π–π stacking structures in single-crystal and film states, as

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

• ) dyes commonly employed nowadays in photoredox catalysis [47], was tested in our reaction. This dye was chosen due to its oxidizing properties, and it ranks among the most oxidizing agents within this class of compounds (E1/2[*PC/PC•−] = +1.56 V vs SCE) [48], but it proved ineffective in our reaction

O,S,Se-containing Biginelli products based on cyclic β-ketosulfone and their postfunctionalization

• Kateryna V. Dil and
• Vitalii A. Palchykov

Beilstein J. Org. Chem. 2024, 20, 2143–2151, doi:10.3762/bjoc.20.184

• organic and medicinal chemists. DHPMs are found in a variety of marine-sourced alkaloids, which are essential for creating biologically active natural products [10]. Some of the DHPM derivatives are also known as functional polymers, adhesives, and fabric dyes [8][12]. In recent decades, the scope of the

A new platform for the synthesis of diketopyrrolopyrrole derivatives via nucleophilic aromatic substitution reactions

• Vitor A. S. Almodovar and
• Augusto C. Tomé

Beilstein J. Org. Chem. 2024, 20, 1933–1939, doi:10.3762/bjoc.20.169

• Vitor A. S. Almodovar Augusto C. Tome LAQV-REQUIMTE, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal 10.3762/bjoc.20.169 Abstract Diketopyrrolopyrroles (DPPs) are a versatile group of dyes and pigments with valuable optoelectronic properties. In this work we report the

• region [3][4]. In turn, N-substituted DPP derivatives are soluble in common organic solvents, exhibit large molar extinction coefficients, Stokes shifts in the range of 10–70 nm and high fluorescence quantum yields [5][6][7]. Due to their outstanding photophysical properties, DPP-based dyes have been

• than the oxygen due to the preferential existence of 4-hydroxypyridine in the pyridin-4-one tautomeric form [37][38][39]. The structures of dyes 3a–f, 4a, 4d and 4f were unambiguously established through their 1H, 13C and 19F NMR and mass spectra. The 1H NMR spectra of the symmetrical compounds

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

• . Different photocatalysts, such as transition metal complexes [23][24], organic dyes [25], and semiconductors [26], can be employed for visible-light-induced chemical processes. The choice of photocatalyst depends on the specific requirements of the catalytic process, including the type of reaction, the

• , such as iridium complexes or organic dyes, and activating agents, including dimethyl dicarbonate (DMDC) and PPh3. Redox-active esters are created when activating agents and carboxylic acids react. These esters can then be reduced using a photoredox catalyst to produce the acyl radical. In 2019, Doyle

Synthesis and optical properties of bis- and tris-alkynyl-2-trifluoromethylquinolines

• Stefan Jopp,
• Franziska Spruner von Mertz,
• Peter Ehlers,
• Alexander Villinger and
• Peter Langer

Beilstein J. Org. Chem. 2024, 20, 1246–1255, doi:10.3762/bjoc.20.107

• ][23], dyes, preservatives and as ligands in complex chemistry [24][25][26][27]. In the context of our interest in the application of cross-coupling reactions to polyhalogenated heterocycles [28][29][30][31], we studied Sonogashira reactions of brominated 2-trifluoromethylquinolines. The optical

Manganese-catalyzed C–C and C–N bond formation with alcohols via borrowing hydrogen or hydrogen auto-transfer

• Mohd Farhan Ansari,
• Atul Kumar Maurya,
• Abhishek Kumar and
• Saravanakumar Elangovan

Beilstein J. Org. Chem. 2024, 20, 1111–1166, doi:10.3762/bjoc.20.98

• are of substantial importance for the fine chemical industry, pharmaceuticals, agrochemicals, dyes, and natural products [25]. The synthesis of amine derivatives can be accomplished using many powerful techniques, including Buchwald–Hartwig and Ullmann cross-coupling reactions, hydroamination

Structure–property relationships in dicyanopyrazinoquinoxalines and their hydrogen-bonding-capable dihydropyrazinoquinoxalinedione derivatives

• Tural N. Akhmedov,
• Ajeet Kumar,
• Daken J. Starkenburg,
• Kyle J. Chesney,
• Khalil A. Abboud,
• Novruz G. Akhmedov,
• Jiangeng Xue and
• Ronald K. Castellano

Beilstein J. Org. Chem. 2024, 20, 1037–1052, doi:10.3762/bjoc.20.92

• groups have extensively developed H-bonded systems including dyes and pigments utilized in organic field-effect transistor (OFET) devices [17][18][19][20]. In two different studies, Głowacki reported H-bonding capable quinacridone and epindolidione-based semiconductors within OFET devices that offer

Carbonylative synthesis and functionalization of indoles

• Alex De Salvo,
• Raffaella Mancuso and
• Xiao-Feng Wu

Beilstein J. Org. Chem. 2024, 20, 973–1000, doi:10.3762/bjoc.20.87

• ring. It was discovered in 1866 by Baeyer and Knop as the basic structure of the natural dye indigo, from which it is derived [1]. The indole ring is a common structural element found in both natural and synthetic products, including pharmaceuticals, agrochemicals, dyes, herbicides, and materials [2][3