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

• (CI) via twisting ground the N=N bond (angle β) returning back to the ground state. Although from the spectral point of view (Figure 1) the obtainment of a mixture of E and Ecis should result in a decrease of intensity of the band around 400 nm, the same process in 3 is very fast to be recorded by

• gives three possible pathways: returning back to ground state by emitting, ESIPT to E* (and relaxation to the ground state by CI in the N=N bond isomerization region) and twisting around the double bond axle C=N (change of α) to the CI in the twisting region populating KE and KK in the ground state. No

• measurable emission of 1 was detected in any of the studied solvents, excluding the first pathway. The ESIPT process is practically barrierless leading to the CI in the N=N bond isomerization region with preferential population of E as discussed above. The third pathway could lead to population of KK, rise

Recent advances in amidyl radical-mediated photocatalytic direct intermolecular hydrogen atom transfer

• Hao-Sen Wang,
• Lin Li,
• Xin Chen,
• Jian-Li Wu,
• Kai Sun,
• Xiao-Lan Chen,
• Ling-Bo Qu and
• Bing Yu

Beilstein J. Org. Chem. 2025, 21, 1306–1323, doi:10.3762/bjoc.21.100

• promoted by the PC radical anion. The resulting anion 32 ultimately produced product 27 through protonation. This system demonstrated the significant HAT capability of amidyl radical 29, as evidenced by the synthesis of products 33, 34, and 35 with yields reaching 70% to 78%. Amidyl radical from N–N bond

Unraveling aromaticity: the dual worlds of pyrazole, pyrazoline, and 3D carborane

• Zahra Noori,
• Miquel Solà,
• Clara Viñas,
• Francesc Teixidor and
• Jordi Poater

Beilstein J. Org. Chem. 2025, 21, 412–420, doi:10.3762/bjoc.21.29

• of the N–N bond in pyrazole might help preserve its aromaticity. To explore this, we performed quantum chemical analyses on a range of o-carborane-fused pyrazoles and pyrazolines and compared them with their fully planar indazole and indazoline analogues. Aromaticity or non-aromaticity can be

• expected to create a hybrid 3D/2D aromatic system, combining the 3D aromaticity of o-carborane with the 2D aromaticity of pyrazole. Notably for the case of pyrazole or pyrazoline, the N–N bond length is diagnostic, being approximately 0.1 Å longer when the molecule lacks aromaticity. In contrast, o

• to exhibit double-bond character. However, these bonds are weaker than a typical single bond. Thus, it is difficult to preserve global aromaticity when combining a 3D aromatic system with a 2D one. The MCI indicator, along with the C–C, C–N, and N–N bond distances – particularly the latter – suggest

Non-covalent organocatalyzed enantioselective cyclization reactions of α,β-unsaturated imines

• Sergio Torres-Oya and
• Mercedes Zurro

Beilstein J. Org. Chem. 2024, 20, 3221–3255, doi:10.3762/bjoc.20.268

• % yield. Finally, the N–N bond could be cleaved forming derivative 58 in 75% yield. All the transformations occurred with the retention of the enantioselectivity. In July 2021, Tian, Wu, Shi and co-workers published a subsequent article of previous work: a chiral phosphoric acid-catalyzed dearomative (2

Multicomponent syntheses of pyrazoles via (3 + 2)-cyclocondensation and (3 + 2)-cycloaddition key steps

• Ignaz Betcke,
• Alissa C. Götzinger,
• Maryna M. Kornet and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2024, 20, 2024–2077, doi:10.3762/bjoc.20.178

Novel oxidative routes to N-arylpyridoindazolium salts

• Oleg A. Levitskiy,
• Yuri K. Grishin and
• Tatiana V. Magdesieva

Beilstein J. Org. Chem. 2024, 20, 1906–1913, doi:10.3762/bjoc.20.166

• -arylpyridoindazolium salts S1–S3 was confirmed with HRMS and 1H, 13C and 19F NMR data; the complete assignment of the signals was performed using 2D NMR methods. The N–N bond formation was additionally confirmed via comparison of the 1H spectra for the salts and their diarylamine precursors. The absence of the signals

Synthesis of 1,2,3-triazoles containing an allomaltol moiety from substituted pyrano[2,3-d]isoxazolones via base-promoted Boulton–Katritzky rearrangement

• Constantine V. Milyutin,
• Andrey N. Komogortsev and
• Boris V. Lichitsky

Beilstein J. Org. Chem. 2024, 20, 1334–1340, doi:10.3762/bjoc.20.117

• , intramolecular recyclization accompanied by opening of the isoxazole ring and formation of the N–N bond leads to intermediate B. Finally, target 1,2,3-triazole 4 is produced via acidification of anion B. Next, we tried to expand the presented rearrangement to hydrazones derived from aliphatic hydrazines (MeNHNH2

Activity assays of NnlA homologs suggest the natural product N-nitroglycine is degraded by diverse bacteria

• Kara A. Strickland,
• Brenda Martinez Rodriguez,
• Ashley A. Holland,
• Shelby Wagner,
• Michelle Luna-Alva,
• David E. Graham and
• Jonathan D. Caranto

Beilstein J. Org. Chem. 2024, 20, 830–840, doi:10.3762/bjoc.20.75

• protect bacteria from exposure to NNG. Keywords: enzymology; natural products; nitramine; N–N bond; Introduction Degradation of nitramines (R–N(R′)NO2; R′ = H or alkyl) has been well studied in the context of the environmental degradation of explosive cyclic nitramines [1][2]. The cyclic nitramines

Identification of the p-coumaric acid biosynthetic gene cluster in Kutzneria albida: insights into the diazotization-dependent deamination pathway

• Seiji Kawai,
• Akito Yamada,
• Yohei Katsuyama and
• Yasuo Ohnishi

Beilstein J. Org. Chem. 2024, 20, 1–11, doi:10.3762/bjoc.20.1

• the ANS pathway, it has been shown that the ANS pathway is involved in the nitrogen–nitrogen (N–N) bond formation in the biosynthesis of several natural products [6][7][8]. Enzymes that catalyze N–N bond formation by using nitrous acid from the ANS pathway have also been characterized in several

Synthesis of N-phenyl- and N-thiazolyl-1H-indazoles by copper-catalyzed intramolecular N-arylation of ortho-chlorinated arylhydrazones

• Yara Cristina Marchioro Barbosa,
• Guilherme Caneppele Paveglio,
• Claudio Martin Pereira de Pereira,
• Sidnei Moura,
• Cristiane Storck Schwalm,
• Gleison Antonio Casagrande and
• Lucas Pizzuti

Beilstein J. Org. Chem. 2022, 18, 1079–1087, doi:10.3762/bjoc.18.110

• cycloaddition reaction of α-diazomethylphosphonates with o-(trimethylsilyl)phenyl triflate in the presence of CsF [13], Cu2+-mediated N−N bond formation from ketimines in the presence of oxygen [14], Pd2+-mediated oxidative benzannulation from pyrazoles and internal alkynes [15], Pd-catalyzed Aza–Nenitzescu

New azodyrecins identified by a genome mining-directed reactivity-based screening

• Atina Rizkiya Choirunnisa,
• Kuga Arima,
• Yo Abe,
• Noritaka Kagaya,
• Kei Kudo,
• Hikaru Suenaga,
• Junko Hashimoto,
• Manabu Fujie,
• Noriyuki Satoh,
• Kazuo Shin-ya,
• Kenichi Matsuda and
• Toshiyuki Wakimoto

Beilstein J. Org. Chem. 2022, 18, 1017–1025, doi:10.3762/bjoc.18.102

• the prediction of the producer of natural products with the functional groups of interest, leading to a higher rate of hits. We recently exploited genome mining targeting hydrazine synthetase and the generation of inorganic hydrazine N2H4 in acid hydrolysate as an indicator of N–N bond-containing

• the discovery of N–N bond-containing natural products from our in-house actinobacterial culture collection, we found two closely related potential biosynthetic gene clusters of aliphatic azoxy natural products in Streptomyces sp. RM72 and Streptomyces sp. A1C6 (Figure 2 and Tables S1 and S2 in

Hydrazides in the reaction with hydroxypyrrolines: less nucleophilicity – more diversity

• Dmitrii A. Shabalin,
• Evgeniya E. Ivanova,
• Igor A. Ushakov,
• Elena Yu. Schmidt and
• Boris A. Trofimov

Beilstein J. Org. Chem. 2021, 17, 319–324, doi:10.3762/bjoc.17.29

• emphasis on the nature of hydrazine derivatives still remains obscure. Meeting this challenge becomes particularly important in view of the significance of the less nucleophilic hydrazides as N–N-bond containing starting materials in drug discovery [13][14][15][16]. Herein, we report how a lower

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• radicals with the formation of a C–O bond (dimer 4b, oxidation of diisopropyl oxime 1b), an O–N bond (dimer 4c, oxidation of benzophenone oxime 1c), and an N–N bond (dimer 4d, oxidation of benzaldoxime 1d, see also [58]) was observed. As a rule, the initial dimers of iminoxyl radicals are unstable, which

A toolbox of molecular photoswitches to modulate the CXCR3 chemokine receptor with light

• Xavier Gómez-Santacana,
• Sabrina M. de Munnik,
• Tamara A. M. Mocking,
• Niels J. Hauwert,
• Shanliang Sun,
• Prashanna Vijayachandran,
• Iwan J. P. de Esch,
• Henry F. Vischer,
• Maikel Wijtmans and
• Rob Leurs

Beilstein J. Org. Chem. 2019, 15, 2509–2523, doi:10.3762/bjoc.15.244

• -isomers are generally assumed to have an intrinsically higher electron density due to the disruption of the conjugation between the two rings of the azobenzene through the N=N bond. Moreover, the electronic properties of the inner substituent Y have been proven to be of strategic use in increasing the

Reversible switching of arylazopyrazole within a metal–organic cage

• Anton I. Hanopolskyi,
• Soumen De,
• Michał J. Białek,
• Yael Diskin-Posner,
• Liat Avram,
• Moran Feller and
• Rafal Klajn

Beilstein J. Org. Chem. 2019, 15, 2398–2407, doi:10.3762/bjoc.15.232

• (Figure 8c, step i). Coordination of Pd2+ to the azo moiety, combined with the strongly electron-donating pyrazole moiety, affords (Figure 8c, step ii) a system akin to push–pull azobenzenes, whose Z isomers can back-isomerize rapidly due to a reduced order of the N=N bond [52][53][54] (Figure 8c, step

Fluorinated azobenzenes as supramolecular halogen-bonding building blocks

• Esther Nieland,
• Oliver Weingart and
• Bernd M. Schmidt

Beilstein J. Org. Chem. 2019, 15, 2013–2019, doi:10.3762/bjoc.15.197

• substituting azobenzenes in the ortho-positions to the N=N bond with electron-withdrawing fluorine substituents [45][46], the red-shifting of the n→π* transitions enables selective addressing of both the E- and Z-isomer using visible light. Stabilization of the n-orbitals in the Z-isomers leads to a very high

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

• coupling to a bulk gold surface via a conjugated linker over 11 bonds and 14 Å [11]. Thermal cis→trans isomerizations of azobenzenes are usually slow with half-lives of the trans-isomer within the range of hours to days at room temperature (parent azobenzene: 4–5 d at 25 °C) [12]. Rotation around the N=N

• bond is a symmetry-forbidden process and the slow isomerization proceeds via inversion at the N atoms [13]. The rate of isomerization is temperature dependent and follows a classical Arrhenius type behavior [12]. However, the rate and the mechanism change dramatically if the azobenzenes are

Synthesis of mono-functionalized S-diazocines via intramolecular Baeyer–Mills reactions

• Miriam Schehr,
• Daniel Hugenbusch,
• Tobias Moje,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2018, 14, 2799–2804, doi:10.3762/bjoc.14.257

• mean plane calculated through the C atoms of 0.014(2) and 0.009(2) Å. The N=N bond lengths of the azo group of 1.251(4) Å corresponds to literature values and the CNNC torsion angle amounts to 3.7(4)°, which proves that this unit is nearly coplanar. In contrast, the CCSC fragment is twisted by 22.9(3

Molecular iodine-catalyzed one-pot multicomponent synthesis of 5-amino-4-(arylselanyl)-1H-pyrazoles

• Camila S. Pires,
• Daniela H. de Oliveira,
• Maria R. B. Pontel,
• Jean C. Kazmierczak,
• Roberta Cargnelutti,
• Diego Alves,
• Raquel G. Jacob and
• Ricardo F. Schumacher

Beilstein J. Org. Chem. 2018, 14, 2789–2798, doi:10.3762/bjoc.14.256

• hydroperoxide in dichloromethane at room temperature for 2 h, the respective diazo aromatic compound 6 could be obtained in 50% yield (Scheme 5). As can be seen, the reaction proceeded smoothly allowing formation of the new N=N bond without cleavage of the C–Se bond under the oxidant media and the presence of

Derivatives of the triaminoguanidinium ion, 5. Acylation of triaminoguanidines leading to symmetrical tris(acylamino)guanidines and mesoionic 1,2,4-triazolium-3-aminides

• Jan Szabo,
• Julian Greiner and
• Gerhard Maas

Beilstein J. Org. Chem. 2017, 13, 579–588, doi:10.3762/bjoc.13.57

• two moieties is indicated by the long C–N bond “c” (as compared to the other C–N bonds in the triazole ring) and the endocyclic N–N bond, both of which have a high single-bond character. The influence of the substituents on the triazole ring of II and 7a on the bond lengths is moderate. The bond

Azobenzene-based inhibitors of human carbonic anhydrase II

• Leander Simon Runtsch,
• David Michael Barber,
• Peter Mayer,
• Michael Groll,
• Dirk Trauner and
• Johannes Broichhagen

Beilstein J. Org. Chem. 2015, 11, 1129–1135, doi:10.3762/bjoc.11.127

• of −143.3° and 23.8° at the N=N bond and at the second aromatic ring to the diazene unit, respectively. It should be noted that a water molecule is held by the peptide backbone in the gorge (2.6 Å to OH of T200 and 2.7 Å to CO of P202), which might have interactions with the diazene unit although the

Photoswitchable precision glycooligomers and their lectin binding

• Daniela Ponader,
• Sinaida Igde,
• Marko Wehle,
• Katharina Märker,
• Mark Santer,
• David Bléger and
• Laura Hartmann

Beilstein J. Org. Chem. 2014, 10, 1603–1612, doi:10.3762/bjoc.10.166

• azobenzene functionalized with an Fmoc-protected aminomethyl group and a carboxylic acid both para to the N=N bond was used as one building block during solid-phase polymer synthesis of precision glycomacromolecules (see AZO, Figure 1) [19][20][21][22]. The benzylamine fragment was favored over the

Use of activated enol ethers in the synthesis of pyrazoles: reactions with hydrazine and a study of pyrazole tautomerism

• Denisa Tarabová,
• Stanislava Šoralová,
• Martin Breza,
• Marek Fronc,
• Wolfgang Holzer and
• Viktor Milata

Beilstein J. Org. Chem. 2014, 10, 752–760, doi:10.3762/bjoc.10.70

• rotated around the N–N bond, with the torsion angle C3–N5–N6–C6 −77.0(2)°, while the N–N bond and adjacent C=C bonds are highly planar with torsion angles 174.09(15)° for C2–C3–N5–N6 and 177.71(16)° for N5–N6–C6–C7. Correspondent bond lengths in the molecule show only minor variations. Three carbonyl

Organocatalytic cascade aza-Michael/hemiacetal reaction between disubstituted hydrazines and α,β-unsaturated aldehydes: Highly diastereo- and enantioselective synthesis of pyrazolidine derivatives

• Zhi-Cong Geng,
• Jian Chen,
• Ning Li,
• Xiao-Fei Huang,
• Yong Zhang,
• Ya-Wen Zhang and
• Xing-Wang Wang

Beilstein J. Org. Chem. 2012, 8, 1710–1720, doi:10.3762/bjoc.8.195

• are of great importance in biological and medicinal chemistry (Figure 1) [1][2][3][4][5]. Besides, pyrazolidines are also important synthetic intermediates in organic chemistry. For instance, the N–N bond of pyrazolidines can be cleaved under reductive conditions to afford useful 1,3-diamines [6][7

Recent advances towards azobenzene-based light-driven real-time information-transmitting materials

• Jaume García-Amorós and
• Dolores Velasco

Beilstein J. Org. Chem. 2012, 8, 1003–1017, doi:10.3762/bjoc.8.113

• electron transfer from the alkoxy group to the pyridinium salt produces a partial breaking of the double N–N bond of the azo moiety, thereby facilitating the rotation around this bond to recover the more stable initial trans configuration in a quick fashion [56]. Type-II azoderivatives: photochromic

• distribution with a simple N–N bond, which seems to be the key to the fast thermal isomerisation kinetics observed. In this way, the rotation around the N–N bond facilitates the recovery of the more stable trans isomer (Figure 14) [46][59][60][61]. The completely different kinetic behaviours observed between

• clearly determined by the intimate mechanism through which the process takes place. This mechanism has attracted much attention for many years and has given rise to controversy. For the process, two different extreme mechanisms have been proposed (Figure 6); one involving a simple rotation around the N–N