Chemical syntheses and salient features of azulene-containing homo- and copolymers

• Vijayendra S. Shetti

Beilstein J. Org. Chem. 2021, 17, 2164–2185, doi:10.3762/bjoc.17.139

• protonation of 17 and 18 by TFA resulted in a large red-shifted broad absorption band in the 500–900 nm region due to the formation of azulenium cations in the polymer backbone unlike the 1,3-polyazulene 5, which had no significant effect on its absorption spectrum upon protonation. The HOMO–LUMO gap for the

• tropylium cations can be achieved by incorporating the seven-membered rings of azulene in the polymer backbone. The enhanced stability of these 4,7-polyazulenes 17–20 in acids and their stimuli-responsible behavior make them potential materials for photonic device applications. Poly[2,6-aminoazulene] In

• , respectively. The UV–vis absorption features of polymers 115 and 116 were altered upon protonation due to the formation of azulenium cations in the polymer backbone and they displayed a significant color change on protonation. None of these polymers were fluorescent in the neutral form, however, 115 and 116

Catalyzed and uncatalyzed procedures for the syntheses of isomeric covalent multi-indolyl hetero non-metallides: an account

• Ranadeep Talukdar

Beilstein J. Org. Chem. 2021, 17, 2102–2122, doi:10.3762/bjoc.17.137

• process, where hydrosilanes 41 were treated with an excess amount of indoles (Scheme 7a and Scheme 7b) [60]. Brookhart’s acid [H(OEt2)2]+[BArF4]− (42) was used to generate ether-stabilized silicon cations of type 46 and norbornene was added as a proton scavenger [64]. Following this procedure, Yonekura

Towards new NIR dyes for free radical photopolymerization processes

• Haifaa Mokbel,
• Guillaume Noirbent,
• Didier Gigmes,
• Frédéric Dumur and
• Jacques Lalevée

Beilstein J. Org. Chem. 2021, 17, 2067–2076, doi:10.3762/bjoc.17.133

• of counter anions and counter cations as well as cyanine structures are discussed. Results and Discussion Synthesis of the different dyes Two different families of cyanines were prepared, differing by the way how the structure is formed. Notably, dyes Ca and Cb differ from the other cyanines by the

Cationic oligonucleotide derivatives and conjugates: A favorable approach for enhanced DNA and RNA targeting oligonucleotides

• Mathias B. Danielsen and
• Jesper Wengel

Beilstein J. Org. Chem. 2021, 17, 1828–1848, doi:10.3762/bjoc.17.125

• , and examining the future design for ASOs. Keywords: antisense oligonucleotides; backbone modifications; cations; nucleobase modifications; sugar modifications; Introduction Antisense oligonucleotides (ASOs) are single-stranded (ss) oligomers composed of typically 10–25 nucleotides linked by

Electron-rich triarylphosphines as nucleophilic catalysts for oxa-Michael reactions

• Susanne M. Fischer,
• Simon Renner,
• A. Daniel Boese and
• Christian Slugovc

Beilstein J. Org. Chem. 2021, 17, 1689–1697, doi:10.3762/bjoc.17.117

• radical cations of the phosphines under investigation were calculated by density functional theory (DFT), namely B3LYP-def2-TZVPPD. According to criterion introduced by Stewart et al. postulating air stability of phosphines when the SOMO energy is higher than −10 eV, the three derivatives should be air

Chemical approaches to discover the full potential of peptide nucleic acids in biomedical applications

• Nikita Brodyagin,
• Martins Katkevics,
• Venubabu Kotikam,
• Christopher A. Ryan and
• Eriks Rozners

Beilstein J. Org. Chem. 2021, 17, 1641–1688, doi:10.3762/bjoc.17.116

• electrostatic repulsion. The maintenance and function of long double-stranded DNA (dsDNA) is achieved through complex mechanisms involving histones and other proteins. Large non-coding RNAs (e.g., ribosomes) manage electrostatic repulsion using positively charged RNA-binding proteins and cations (e.g

Icilio Guareschi and his amazing “1897 reaction”

• Gian Cesare Tron,
• Alberto Minassi,
• Giovanni Sorba,
• Mara Fausone and
• Giovanni Appendino

Beilstein J. Org. Chem. 2021, 17, 1335–1351, doi:10.3762/bjoc.17.93

• alcohol side product was not labeled, suggesting that alcohols are formed by radical trapping by oxygen and the intermediate formation of hydroperoxides. Conversely, cations would have been trapped by water, resulting in the formation of labeled alcohols. Cyclic voltammetry experiments showed an

Photoinduced post-modification of graphitic carbon nitride-embedded hydrogels: synthesis of 'hydrophobic hydrogels' and pore substructuring

• Cansu Esen and
• Baris Kumru

Beilstein J. Org. Chem. 2021, 17, 1323–1334, doi:10.3762/bjoc.17.92

• +) releasing performances of HGCM and HGCM-vTA after an overnight immersion in separately prepared stock solutions were analysed via ICP-OES (Supporting Information File 1, Figure S4b). HGCM shows higher cation releasing which might be driven by osmosis, however, HGCM-vTA retains cations thus offering a slower

• Scan spectrophotometer equipped with an integrating sphere. Thermogravimetric analysis (TGA) was performed via TG 209 Libra from Netzsch under nitrogen atmosphere with a heating rate 10 K min−1 using aluminum crucible for samples. Trace analysis of potassium, calcium and magnesium cations were

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

Synthesis of trifluoromethyl ketones by nucleophilic trifluoromethylation of esters under a fluoroform/KHMDS/triglyme system

• Yamato Fujihira,
• Yumeng Liang,
• Makoto Ono,
• Kazuki Hirano,
• Takumi Kagawa and
• Norio Shibata

Beilstein J. Org. Chem. 2021, 17, 431–438, doi:10.3762/bjoc.17.39

• highly stable fluoride salts (MF), the breakdown of CF3− into difluorocarbene in the presence of alkali (M+) and other metal cations is favored. In earlier studies, the solvent N,N-dimethylformamide (DMF), was essential for nucleophilic trifluoromethylation by HCF3 since DMF acts as a CF3 anion reservoir

Helicene synthesis by Brønsted acid-catalyzed cycloaromatization in HFIP [(CF₃)₂CHOH]

• Takeshi Fujita,
• Noriaki Shoji,
• Nao Yoshikawa and
• Junji Ichikawa

Beilstein J. Org. Chem. 2021, 17, 396–403, doi:10.3762/bjoc.17.35

• fluorine, which helps to generate cations but does not affect cationic reactions [23][24][25][26][27]. Thus, HFIP greatly facilitates reactions via cationic intermediates [28]. In the presence of a catalytic amount of trifluoromethanesulfonic acid in HFIP, (biaryl-2-yl)acetoaldehydes or their acetal

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• cations is probably the α-(trifluoromethyl) carbocation. Many efforts are currently devoted to develop methods allowing the efficient insertion of fluorine atoms or fluorinated groups into organic molecules [7][8][9][10][11][12]. The increasing demand for fluorinated scaffolds, due to the striking

• environment will be scrutinized. The chapter will summarize kinetic studies and concomitant theoretical investigations on the cations formation and stability data as well as synthetic perspectives offered by the studied carbenium ions. Any discussion of the results coming from the ionization of perfluorinated

Au(III) complexes with tetradentate-cyclam-based ligands

• Ann Christin Reiersølmoen,
• Thomas N. Solvi and
• Anne Fiksdahl

Beilstein J. Org. Chem. 2021, 17, 186–192, doi:10.3762/bjoc.17.18

• binding properties [25] and reactions with bovine serum albumin [27]. Cyclam is known as a tetraamino-macrocyclic ligand, which binds strongly to give complexes with many transition metal cations. While catalytic applications of square planar cyclam complexes are reported for metals, such as Ni [30][31

Multiswitchable photoacid–hydroxyflavylium–polyelectrolyte nano-assemblies

• Alexander Zika and
• Franziska Gröhn

Beilstein J. Org. Chem. 2021, 17, 166–185, doi:10.3762/bjoc.17.17

• , systems which respond to more than one external trigger have become of great interest [68][69][70][71][72][73]. Hydroxyflavylium cations can exhibit a network of different chemical reactions enabling these molecules to perform as a molecular level optical memory [74][75][76][77][78]. The network of

• understood with the fact that likely not every anionic charge can interact with a cationic charge due to steric reasons. No more ionically driven association occurs at even lower loading ratios for l < 0.16 as there are too many cations in the assemblies. The results for the assemblies at pH 5.0 are similar

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• ]arene. Pillararenes have electron-rich cavities that facilitate the combination with various electron-deficient guest molecules, such as alkylammonium, pyridinium, and imidazolium cations. Compared to other macrocycles, pillararenes exhibit a high degree of symmetry and rigidity, which gives them a

Direct synthesis of anomeric tetrazolyl iminosugars from sugar-derived lactams

• Michał M. Więcław and
• Bartłomiej Furman

Beilstein J. Org. Chem. 2021, 17, 115–123, doi:10.3762/bjoc.17.12

• conformer. Therefore, once the ground conformer of the oxocarbenium ion is established, this logic may be used to predict the reaction’s stereochemistry. The same principle may be successfully applied to reactions of iminium cations. We have previously shown that in the case of glucose- and galactose

• new, chiral 2-(tetrazol-5-yl)-iminosugar based potential organocatalyst. Principle behind Woerpel’s model for prediction of the direction of nucleophile addition to oxocarbenium cations. Difference in conformational stability of glucose- and galactose-derived iminium cations and the major product of

Metal-free synthesis of biarenes via photoextrusion in di(tri)aryl phosphates

• Hisham Qrareya,
• Lorenzo Meazza,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 3008–3014, doi:10.3762/bjoc.16.250

• intermediates (triplet aryl cations [28][29] or aryl radicals [30][31]). As for the former case, the intermolecular formation of a biaryl arose from the photoheterolysis of an Ar–N bond (in arene diazonium salts or their derivatives [32][33]), of an Ar–Cl bond [34][35], of an Ar–O bond (in aryl phosphates [36

• investigations in the last decades [28][29][64][68]. Simple (electron-rich) monoaryl phosphates are known to undergo the photoheterolysis of the Ar–O bond to form aryl cations [28][36]. The presence of an electron-withdrawing group (e.g., NO2) may, however, divert the reactivity since a photoinduced solvolysis

• the presence of increasing amounts of TFE (up to 20% v/v, continuous line). Synthesis of biarenes via a) photogenerated triplet aryl cations and aryl radicals (PC = photocatalyst), b) intramolecular free radical ipso substitution, c) thermally catalyzed extrusion of CO and SO2, d) photoinduced

Chiral anion recognition using calix[4]arene-based ureido receptors in a 1,3-alternate conformation

• Tereza Horáčková,
• Jan Budka,
• Vaclav Eigner,
• Wen-Sheng Chung,
• Petra Cuřínová and
• Pavel Lhoták

Beilstein J. Org. Chem. 2020, 16, 2999–3007, doi:10.3762/bjoc.16.249

• -containing onium salts, protonated or alkylated aza-crown ethers and azacryptands, amidinium and guanidinium cations, etc. [15][16][17][18]. Due to the low directionality of the Coulomb force, the successful application of purely ionic interactions in the design of selective anion receptors is rather limited

Controlled decomposition of SF₆ by electrochemical reduction

• Sébastien Bouvet,
• Bruce Pégot,
• Stéphane Sengmany,
• Erwan Le Gall,
• Eric Léonel,
• Anne-Marie Goncalves and
• Emmanuel Magnier

Beilstein J. Org. Chem. 2020, 16, 2948–2953, doi:10.3762/bjoc.16.244

• disappearance of SF6 after 6 hours as well as all the fluorinated organic compounds. The only peak detected by 19F NMR is around −153 ppm. This value corresponds to the classical chemical shift range of a fluoride anion. Due to its broad appearance, we can postulate the association with cations coming from the

On the mass spectrometric fragmentations of the bacterial sesterterpenes sestermobaraenes A–C

• Anwei Hou and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2020, 16, 2807–2819, doi:10.3762/bjoc.16.231

• bacteria, that is characterised by an aspartate-rich motif (DDXXD) and an NSE triad (NDLXSXXXE) for binding of a trinuclear Mg2+ cluster [2][3]. The Mg2+ cations in turn bind to the diphosphate moiety of an isoprenoid diphosphate precursor and cause substrate ionisation by a diphosphate abstraction to

A heterobimetallic tetrahedron from a linear platinum(II)-bis(acetylide) metalloligand

• Matthias Hardy,
• Marianne Engeser and
• Arne Lützen

Beilstein J. Org. Chem. 2020, 16, 2701–2708, doi:10.3762/bjoc.16.220

• (acetylide)platinum(II) complex [Pt(L1)2(PBu3)2] as a linear metalloligand. The reaction of this metalloligand with iron(II) cations and pyridine-2-carbaldehyde according to the subcomponent self-assembly approach yielded decanuclear heterobimetallic tetrahedron [Fe4Pt6(L2)12](OTf)8. Thus, combination of

• complexity with homometallic assemblies becomes increasingly difficult to achieve. An approach to tackle these limitations is the use of not only one, but two different types of metal cations to form heterobimetallic aggregates [24][25][26]. Introducing two different types of metal cations within one

• chance to obtain new geometries, the combination of two different metal cations within one aggregate might also lead to enhanced or even entirely new properties and functions [40]. Searching the literature, however, it is striking that the number of heterobimetallic tetrahedra [41][42] is noticeably

Synthesis and characterization of S,N-heterotetracenes

• Astrid Vogt,
• Florian Henne,
• Christoph Wetzel,
• Elena Mena-Osteritz and
• Peter Bäuerle

Beilstein J. Org. Chem. 2020, 16, 2636–2644, doi:10.3762/bjoc.16.214

• TTA, SN4 9, and SN4'' 33 irreversible oxidation waves were obtained due to follow-up reactions of the formed radical cations and peak potentials gradually decrease from 0.81 V for TTA to 0.07 V for SN4'' 33 (Figure 2, right). As expected, the oxidation potential is substantially influenced by the

Anion exchange resins in phosphate form as versatile carriers for the reactions catalyzed by nucleoside phosphorylases

• Julia N. Artsemyeva,
• Ekaterina A. Remeeva,
• Tatiana N. Buravskaya,
• Irina D. Konstantinova,
• Roman S. Esipov,
• Anatoly I. Miroshnikov,
• Natalia M. Litvinko and
• Igor A. Mikhailopulo

Beilstein J. Org. Chem. 2020, 16, 2607–2622, doi:10.3762/bjoc.16.212

• found that phosphorolysis of uridine, thymidine, and Ara-U in the presence of Dowex® 1X8 (phosphate; Dowex-nPi) proceeded smoothly in the presence of magnesium cations in water at 20–50 °C for 54–96 h giving rise to quantitative formation of the corresponding pyrimidine bases and PF-1Pis. The resulting

Thermodynamic and electrochemical study of tailor-made crown ethers for redox-switchable (pseudo)rotaxanes

• Henrik Hupatz,
• Marius Gaedke,
• Hendrik V. Schröder,
• Julia Beerhues,
• Arto Valkonen,
• Fabian Klautzsch,
• Sebastian Müller,
• Felix Witte,
• Kari Rissanen,
• Biprajit Sarkar and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2020, 16, 2576–2588, doi:10.3762/bjoc.16.209

• ferrocene [14][17]. Yet, switchable crown ethers are also widely applied as cation sensors, where the sensor activity can be controlled by external stimuli, e.g., light, the redox potential or chemical reagents [14][17]. Redox-switchable crown ethers have been shown to sense cations by the generation of an

• electrochemical output. For example, crown ethers containing tetrathiafulvalene (TTF) derivatives, which enable two reversible oxidation processes from the neutral to the dicationic state, were applied to sense various cations, e.g., alkali metal ions, Pb2+, and Ba2+ [18][19][20][21]. Furthermore, with the first

Water-soluble host–guest complexes between fullerenes and a sugar-functionalized tribenzotriquinacene assembling to microspheres

• Si-Yuan Liu,
• Xin-Rui Wang,
• Man-Ping Li,
• Wen-Rong Xu and
• Dietmar Kuck

Beilstein J. Org. Chem. 2020, 16, 2551–2561, doi:10.3762/bjoc.16.207

• sodium cations requires further studies. Despite the unusual mass spectrometric behavior of the compound, the combined spectroscopic evidence strongly supports the identity of TBTQ-(OAcG)6. After deprotection of the glucose units, the acetyl signals disappeared in the 1H and 13C NMR spectra of the target