The effect of neighbouring group participation and possible long range remote group participation in O-glycosylation

• Rituparna Das and
• Balaram Mukhopadhyay

Beilstein J. Org. Chem. 2025, 21, 369–406, doi:10.3762/bjoc.21.27

• directions away from the central oxocarbenium ion intermediate in the limiting dissociative process involving diastereomeric ion pairs. Destabilisation and greater reactivity of the oxocarbenium intermediate causes the nucleophilic acceptor moiety to attack in a concerted process following a classical SN2

• the extremes of SN1 and SN2 pathway by employing the effect of counter ions, showing close resemblance with the SNi mechanism [41], conforming to the famous Winstein’s ion-pair theory [42] and draws analogy with chlorination of alcohols by thionyl chloride [43]. Incorporating the role of counter ion

• pairs in glycosylation mechanisms was first reported by Rhind-Tutt and Vernon [44], and later reiterated by various authors, including the seminal graphical analysis of Lemieux and co-workers [45][46][47]. Thus, complete categorisation of the reaction in either of the subdomains of substitution reaction

Advances in the use of metal-free tetrapyrrolic macrocycles as catalysts

• Mandeep K. Chahal

Beilstein J. Org. Chem. 2024, 20, 3085–3112, doi:10.3762/bjoc.20.257

• metal-free porphyrins. 1.1 Calix[4]pyrrole macrocycles as organocatalysts Calix[4]pyrroles act as versatile ligands in supramolecular chemistry and have been widely studied as binding hosts for various guests such as anions, ion pairs, or neutral compounds [4][30][31], ligands for p-block elements, as

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

• Yohei Haketa Takuma Matsuda Hiromitsu Maeda Department of Applied Chemistry, College of Life Sciences, Ritsumeikan University, Kusatsu 525–8577, Japan 10.3762/bjoc.20.215 Abstract Ion pairs of N-(2,6-dimethylphenyl)-substituted triazatriangulenium (TATA+) cation with various counteranions were

• synthesized to investigate the interactions for the bulky cation. Single-crystal X-ray analysis of the TATA+ ion pairs revealed solid-state ion-pairing assemblies without stacking at the cationic π-planes. The TATA+ cation showed counteranion-dependent assembly structures, with smaller counteranions located

• at the top of TATA+ and bulkier counteranions displaced from the TATA+ plane to interact with the surrounding TATA+. Keywords: charged π-electronic systems; ion pairs; single-crystal X-ray analysis; solid-state assemblies; triazatriangulenium cation; Introduction Triangulenium cations [1][2] have

Stability trends in carbocation intermediates stemming from germacrene A and hedycaryol

• Naziha Tarannam,
• Prashant Kumar Gupta,
• Shani Zev and
• Dan Thomas Major

Beilstein J. Org. Chem. 2024, 20, 1189–1197, doi:10.3762/bjoc.20.101

• (GPP, FPP, GGPP) undergo highly complex cyclisation cascades forming terpenes and terpenoids that often have great structural complexity. For class I terpene synthases this multistep process is initiated by a heterolytic C–O bond cleavage, separating the diphosphate and isoprenoid ion pairs [3][4]. The

Ligand effects, solvent cooperation, and large kinetic solvent deuterium isotope effects in gold(I)-catalyzed intramolecular alkene hydroamination

• Ruichen Lan,
• Brock Yager,
• Yoonsun Jee,
• Cynthia S. Day and
• Amanda C. Jones

Beilstein J. Org. Chem. 2024, 20, 479–496, doi:10.3762/bjoc.20.43

• -workers found a reversal of enantioselectivity that can be controlled by choice of solvent, which they rationalized by invoking a solvent induced change in ion-pairs [6]. In another study by Agbossou-Niedercorn, Michon, and co-workers, they found that chiral alcohols do not impact enantioselectivity [7

Trifluoromethylated hydrazones and acylhydrazones as potent nitrogen-containing fluorinated building blocks

• Zhang Dongxu

Beilstein J. Org. Chem. 2023, 19, 1741–1754, doi:10.3762/bjoc.19.127

• conditions [38] (Scheme 2). Moreover, a chiral Brønsted acid-catalyzed asymmetric 6π electrocyclization of trifluoroacetaldehyde hydrazones for the synthesis of enantiomerically enriched 3-trifluoromethyl-1,4-dihydropyridazines was first developed by Rueping et al. [39]. The strategy involves chiral ion

• pairs and provides a good basis and scope for further extensions and explorations [39] (Scheme 3). Based on the work by Wu et al. and extending their previous work, Rueping and co-workers explored the effects of fluorine in organocatalytic reactions. They developed an asymmetric Brønsted acid–Lewis base

Tying a knot between crown ethers and porphyrins

• Maksym Matviyishyn and
• Bartosz Szyszko

Beilstein J. Org. Chem. 2023, 19, 1630–1650, doi:10.3762/bjoc.19.120

• multitopic receptors capable of binding ions and ion-pairs, which have been used in ion binding and catalysis, to name a few applications [47][48][49]. A primary example of a crown ether-annulated porphyrin, i.e., β-crowned porphyrin, was established in 1996 by Murashima and co-workers [50]. The macrocycle

• complex was created, where both ions were held in close proximity. It was further reported that 5 could adapt its binding behaviour depending on the counteranion in the caesium salt. Later Sessler and co-workers used naphthocrown-strapped calix[4]pyrrole 6 as a host to entrap CsF or CsCl ion pairs [103

• ]. The CsF binding led to a supramolecular self-assembly process, inducing a sandwich host–guest complex formation in the solid state (Scheme 2). It was established that fluoride is preferred over any other halide anions. The binding of the ion pairs was observed in highly polar solvent media, but in the

Halides as versatile anions in asymmetric anion-binding organocatalysis

• Lukas Schifferer,
• Martin Stinglhamer,
• Kirandeep Kaur and
• Olga García Macheño

Beilstein J. Org. Chem. 2021, 17, 2270–2286, doi:10.3762/bjoc.17.145

• solvent-separated or solvent-shared ion pairs – in which the components have their own solvent shells –, nonpolar solvents are more likely to lead to contact-ion pairs. As such, the cation and anion are in closer proximity as one solvent shell is shared. If a chiral catalyst binds then to the anion, a

Regioselective N-alkylation of the 1H-indazole scaffold; ring substituent and N-alkylating reagent effects on regioisomeric distribution

• Ryan M. Alam and
• John J. Keating

Beilstein J. Org. Chem. 2021, 17, 1939–1951, doi:10.3762/bjoc.17.127

• 1H-indazole, employing NaHMDS in tetrahydrofuran (THF) or dimethyl sulfoxide (DMSO), and observed solvent-dependent regioselectivity [24]. Mechanistic hypotheses, based on elegant experimentation, were proposed to underline the roles that tight and solvent-separated ion pairs played in the observed

• alkylation to the N-1 position. Furthermore, this effect is not observed for indazoles bearing C-3 substituents that cannot participate in the formation of tight ion pairs (such as, 12–18 and 20), under conditions A (NaH in THF). The latter N-1 regioselectivity conferred through tight ion pair formation is

• DMSO instead of THF as the reaction solvent [24]. It is likely that DMF similarly facilitates the formation of solvent-separated ion pairs which serve to diminish the high N-1 regioselectivity previously achieved when using THF (Table 3, entry 2), where tight ion pair formation between the cesium

Metal-free glycosylation with glycosyl fluorides in liquid SO₂

• Krista Gulbe,
• Jevgeņija Lugiņina,
• Edijs Jansons,
• Artis Kinens and
• Māris Turks

Beilstein J. Org. Chem. 2021, 17, 964–976, doi:10.3762/bjoc.17.78

• during the glycosylation with glycosyl fluorides in liquid SO2 is proved by 19F NMR spectroscopy. A sulfur dioxide-assisted glycosylation mechanism that proceeds via solvent separated ion pairs is proposed, whereas the observed α,β-selectivity is substrate-controlled and depends on the thermodynamic

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

• - or dibromomethyl carbanions. The so-obtained carbanions form lipophilic ion pairs with the catalyst cation and move into the organic phase, where they react with dibromodifluoromethane. Consequently, carbon tetrabromide (or bromoform) and the ion pair CBrF2−N+Bu4 are formed. The ion pair decomposes

Selected peptide-based fluorescent probes for biological applications

• Debabrata Maity

Beilstein J. Org. Chem. 2020, 16, 2971–2982, doi:10.3762/bjoc.16.247

• ). The inhibition by peptide 9 is found to be in a reversible and noncompetitive way. Molecular modeling shows four cationic ammonium groups forming ion pairs and hydrogen bonds with negatively charged residues, such as Glu217, Asp60B, Asp147 and Glu217, respectively and completely block the central pore

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

• binding constant, but enthalpic and entropic contributions have not yet been studied [50][51][55]. As PF6− is more strongly coordinating than BArF24−, a larger fraction of A1·PF6 ion pairs is present in nonpolar solvents such as DCE. Upon complexation, the ion pair of A1·PF6 must dissociate, releasing PF6

Automated high-content imaging for cellular uptake, from the Schmuck cation to the latest cyclic oligochalcogenides

• Rémi Martinent,
• Javier López-Andarias,
• Dimitri Moreau,
• Yangyang Cheng,
• Naomi Sakai and
• Stefan Matile

Beilstein J. Org. Chem. 2020, 16, 2007–2016, doi:10.3762/bjoc.16.167

• ]. Firstly, in comparison to simple guanidinium cations 2 (pKa 12.5) and ammonium cations 3 (pKa 10.5), the Schmuck cation has a lower pKa value of 7 to 8 due to the increased acidity of acylguanidiniums, which favors the formation of stronger hydrogen-bonded ion pairs (Figure 1, magenta part). Secondly, the

Exploring the scope of DBU-promoted amidations of 7-methoxycarbonylpterin

• Anna R. Bockman and
• Jeffrey M. Pruet

Beilstein J. Org. Chem. 2020, 16, 509–514, doi:10.3762/bjoc.16.46

• ion pairs with the cationic DBU-activated acyl intermediate (see Figure 1). However, the α-substitution in alanine clearly abolishes any rate acceleration driven by ionic interactions, and most α-substituted amines had similar rates. Rate acceleration is recovered in serine, owing to the effect of the

Anion-driven encapsulation of cationic guests inside pyridine[4]arene dimers

• Anniina Kiesilä,
• Jani O. Moilanen,
• Anneli Kruve,
• Christoph A. Schalley,
• Perdita Barran and
• Elina Kalenius

Beilstein J. Org. Chem. 2019, 15, 2486–2492, doi:10.3762/bjoc.15.241

• the coordination of the Me4N+ cation at the lower rim has only a minor effect on the hydrogen-bond network of 12. To verify complexation of separate ion pairs, the geometry optimization was carried out also for [12 + Me4Nendo + Iendo] , which showed that the cavity of 12 is too small for the

Small anion-assisted electrochemical potential splitting in a new series of bistriarylamine derivatives: organic mixed valency across a urea bridge and zwitterionization

• Keishiro Tahara,
• Tetsufumi Nakakita,
• Alyona A. Starikova,
• Takashi Ikeda,
• Masaaki Abe and
• Jun-ichi Kikuchi

Beilstein J. Org. Chem. 2019, 15, 2277–2286, doi:10.3762/bjoc.15.220

• of larger counteranions increase because they do not form strong ion-pairs with charged species, enhancing electrostatic interactions between redox components [46][47][48][49][50][51][52]. Thus, a different mechanism is proposed to explain the present effects of the supporting electrolytes in terms

Complexation of chiral amines by resorcin[4]arene sulfonic acids in polar media – circular dichroism and diffusion studies of chirality transfer and solvent dependence

• Bartosz Setner and
• Agnieszka Szumna

Beilstein J. Org. Chem. 2019, 15, 1913–1924, doi:10.3762/bjoc.15.187

• direct evidence that the complexes are tight ion-pairs with an ordered structure comes from the diastereotopic splitting of the CH2SO3− groups of 1 (insets in Figure 2a–g). Such splitting can only be present when chirality of the guest is transferred into the host and the effect is not averaged by

Transient and intermediate carbocations in ruthenium tetroxide oxidation of saturated rings

• Manuel Pedrón,
• Laura Legnani,
• Maria-Assunta Chiacchio,
• Pierluigi Caramella,
• Tomás Tejero and
• Pedro Merino

Beilstein J. Org. Chem. 2019, 15, 1552–1562, doi:10.3762/bjoc.15.158

• corresponding ion pairs failed, ending at the final P1–3 products and confirming that they are not stationary points. However, this does not mean that they cannot exist in the form of transient species as we have recently demonstrated [38]. A completely different situation was found with the oxidation of N

• oxidation was only 0.3 kcal/mol suggesting a directing effect of the p-methoxyphenyl group. Notably, the IRC analyses of the transition structures revealed as end points of the reactions the ion pairs IN4,5. Indeed, optimization of those points led to IN4a, IN5a and IN5b as energy minima; only IN4b could

• not be located, the optimization of which led to P4b. Transformation of ion pairs into the corresponding products P4a and P5a,b was found to be essentially barrierless. As expected, the ion pairs identified as minima adopt the form of an iminium ion, the most stable being IN5b, corresponding to that

Molecular recognition using tetralactam macrocycles with parallel aromatic sidewalls

• Dong-Hao Li and
• Bradley D. Smith

Beilstein J. Org. Chem. 2019, 15, 1086–1095, doi:10.3762/bjoc.15.105

• enables them to be effective hosts for a wide range of guest molecules including organic biscarbonyl derivatives, near-infrared dyes, acenes, precious metal halide complexes, trimethylammonium ion-pairs, and saccharides. Keywords: fluorescent dye; host–guest chemistry; hydrogen bonding; hydrophobic

•  5c). In addition, the peripheral methyl groups on each sidewall in C provide stabilizing CH···X interactions. 3.4. Ammonium chloride ion pairs Another advantage of the amphiphilic macrocyclic cavity was recently uncovered by studies that showed simultaneous binding of tetralkylammonium chloride ion

• pairs, such as acetylcholine chloride, 26+·Cl−, by tetralactam B [64]. As shown in Figure 6, the cavity can nicely accommodate ion pairs that can simultaneously contact the NH residues and the interior aromatic surfaces. The cavity was an especially good fit for trimethylbenzylammonium chloride salts

Design, synthesis and spectroscopic properties of crown ether-capped dibenzotetraaza[14]annulenes

• Krzysztof M. Zwoliński and
• Julita Eilmes

Beilstein J. Org. Chem. 2019, 15, 617–622, doi:10.3762/bjoc.15.57

• whole ion pairs within the same superstructure [30], we decided to combine the two macrocyclic building blocks within the same rigidified architecture. Therefore, novel ‘crown-capped’ receptors 3a and 3b were designed to be composed of diaza-crown ether and DBTAA macrocycles. Arrangement of the two

• satisfactory 26–28% isolated yields and fully characterized based on HR-ESIMS, FTIR-ATR, 1H and 13C NMR spectroscopy and elemental analysis. These novel receptors are expected to bind both the transition, alkali and alkaline-earth metals, and also, after DBTAA subunit metalation the whole ion pairs. The

Silanediol versus chlorosilanol: hydrolyses and hydrogen-bonding catalyses with fenchole-based silanes

• Falco Fox,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2019, 15, 167–186, doi:10.3762/bjoc.15.17

• % ee), reaction of 1-chloroisochroman (18) and silyl ketene acetals 11 (up to 85% yield and 5% ee), reaction of chromen-4-one (20) and silyl ketene acetals 11 (up to 98% yield and 4% ee). Keywords: hydrogen bonds; hydrolysis; ion pairs; organocatalysis; silanediol; Introduction Silanediols are

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

An overview of recent advances in duplex DNA recognition by small molecules

• Sayantan Bhaduri,
• Nihar Ranjan and
• Dev P. Arya

Beilstein J. Org. Chem. 2018, 14, 1051–1086, doi:10.3762/bjoc.14.93

• Dervan hairpin polyamide was synthesized. The resulting conjugate 25 binds A·T-rich DNA duplexes with comparable affinity to that of the parent polyamide and breaks one strand of double-stranded plasmid DNA by interacting with anionic phosphodiesters in a fast transphosphorylation step as contact ion

• pairs at micromolar to high nanomolar concentration range [91]. Richert et al. designed a novel set of three-pronged probes (TPPs) comprising of cap, β-alanines and oligopyrrolamides in order to bind A·T-rich target strands from three sides (Watson–Crick face, terminus, and minor groove) resulting in

Liquid-assisted grinding and ion pairing regulates percentage conversion and diastereoselectivity of the Wittig reaction under mechanochemical conditions

• Kendra Leahy Denlinger,
• Lianna Ortiz-Trankina,
• Preston Carr,
• Kingsley Benson,
• Daniel C. Waddell and
• James Mack

Beilstein J. Org. Chem. 2018, 14, 688–696, doi:10.3762/bjoc.14.57

• the same rationale could be used in the case of our solvent-free conditions. In solution, ions are separated and stabilized by solvent molecules. Mechanistically we envision ions to start out as contact ion pairs, then solvent separated ion pairs (i.e., loose ion pairs) followed by free ion pairs

• . Conclusion Both a high dielectric constant of the solvent used in liquid-assisted grinding (LAG) and proper ion pairing were found to increase the percent conversion to stilbenes under mechanochemical conditions. Choosing appropriate ion pairs when LAG is utilized in the system also allowed tuning the