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

Synthesis of a sucrose-based macrocycle with unsymmetrical monosaccharides "arms"

• Karolina Tiara,
• Mykhaylo A. Potopnyk and
• Sławomir Jarosz

Beilstein J. Org. Chem. 2018, 14, 634–641, doi:10.3762/bjoc.14.50

• ; Introduction Chiral macrocyclic compounds play an important role in supramolecular and biological systems [1][2]. Many of them serve as convenient receptors for cations [3], anions [4], ion pairs [5], neutral molecules [6] etc. Binaphthols [7][8][9], amino acids [10], chiral diamines [11][12], carbohydrates

Stereochemical outcomes of C–F activation reactions of benzyl fluoride

• Neil S. Keddie,
• Pier Alexandre Champagne,
• Justine Desroches,
• Jean-François Paquin and
• David O'Hagan

Beilstein J. Org. Chem. 2018, 14, 106–113, doi:10.3762/bjoc.14.6

• (C) ion pairs. The partial racemization observed in Table 3 suggests that the solvent-separated ion-pair intermediate (C) is most likely the reactive species, as it would naturally lead to a partial racemization of the substrate stereocenter. When the activator was changed from HFIP to a mixed system

Chiral phase-transfer catalysis in the asymmetric α-heterofunctionalization of prochiral nucleophiles

• Johannes Schörgenhumer,
• Maximilian Tiffner and
• Mario Waser

Beilstein J. Org. Chem. 2017, 13, 1753–1769, doi:10.3762/bjoc.13.170

• major advantages of all these chiral cation-based phase-transfer catalysts (Q+ X−) is their unique potential to control the reactivity of a broad variety of different prochiral nucleophiles (i.e., enolates) via formation of chiral ion pairs, which can then undergo stereoselective α-functionalization

Block copolymers from ionic liquids for the preparation of thin carbonaceous shells

• Sadaf Hanif,
• Bernd Oschmann,
• Dmitri Spetter,
• Muhammad Nawaz Tahir,
• Wolfgang Tremel and
• Rudolf Zentel

Beilstein J. Org. Chem. 2017, 13, 1693–1701, doi:10.3762/bjoc.13.163

• ; ionic liquid; polymeric ionic liquid; RAFT polymerization; Introduction Ionic liquids (ILs) are organic salts. Most of them have a melting point below 100 °C [1][2]. These organic salts do not have the same structure like inorganic salts. This is due to the structure of the ion pairs. They are built of

Substitution of fluorine in M[C₆F₅BF₃] with organolithium compounds: distinctions between O- and N-nucleophiles

• Anton Yu. Shabalin,
• Nicolay Yu. Adonin and
• Vadim V. Bardin

Beilstein J. Org. Chem. 2017, 13, 703–713, doi:10.3762/bjoc.13.69

• solvent molecules to form contact ion pair [37]. The opposite situation is in 1-N where the bulky tetrabutylammonium cation (“soft”) interacts with those fluorine atom(s) weaker than Li+ either in DME and diglyme and this salt forms solvent-separated ion pairs. Potassium pentafluorophenyltrifluoroborate

• is the intermediate position. The 11B and 19F NMR chemical shifts of BF3 group in 1-K in DME are closely related to the shifts of 1-Li in the same solvents and reflect the formation of contact ion pairs. In acetonitrile the salts 1-Li and 1-N form solvent-separated ion pairs (11B and 19F NMR). These

• observations eludicate the effect of counteractions on the isomer compositions of M[RC6F4BF3]. In DME both salts, 1-Li and 1-K, exist as the contact ion pairs and thus the molar ratios of [4-BuC6F4BF3]−/[2-BuC6F4BF3]− should be similar. Indeed, the ratio of these products derived from 1-Li and 1-K are 1:0.15

New approaches to organocatalysis based on C–H and C–X bonding for electrophilic substrate activation

• Pavel Nagorny and
• Zhankui Sun

Beilstein J. Org. Chem. 2016, 12, 2834–2848, doi:10.3762/bjoc.12.283

• form the corresponding salts, and these generated in situ ion pairs were treated with silyl enol ethers in the presence of chiral catalysts L2–L4 to form chiral addition products. High levels of chirality transfer were generally observed for various 6-membered nitrogen-containing heterocyclic

A chiral analog of the bicyclic guanidine TBD: synthesis, structure and Brønsted base catalysis

• Mariano Goldberg,
• Denis Sartakov,
• Jan W. Bats,
• Michael Bolte and
• Michael W. Göbel

Beilstein J. Org. Chem. 2016, 12, 1870–1876, doi:10.3762/bjoc.12.176

• amino acid arginine, they play an important role in biochemistry, mainly by forming ion pairs. In addition, numerous guanidine derivatives with complex cyclic structures can be found in natural products [1]. Simple guanidines such as tetramethylguanidine have been used as strong Brønsted bases in

• contains two cations, two benzoate anions and ethyl acetate as a solvate molecule. Each cation is connected by two N–H···O hydrogen bonds to benzoate ions. The rings of cation 10 adopt a conformation close to an envelope with the phenyl substituents in pseudo-axial positions. The ion pairs and the solvate

• configuration, it also forms S,S-25 preferentially. Accordingly, transition-state structures in the reactions of guanidines 8 and 10 must differ from each other. Structure of guanidines 1–10. Crystal structure of guanidine 10 as a benzoate salt. Only one of the ion pairs is shown for the sake of clarity. A

Creating molecular macrocycles for anion recognition

• Amar H. Flood

Beilstein J. Org. Chem. 2016, 12, 611–627, doi:10.3762/bjoc.12.60

• ion pairs (Kip). As a tribute to the four equilibria and the four species that are formed, the 1H NMR titration data for triazolophane 7 is exemplary (Figures 9b,c). Proton Ha reflects the 1:1 species by stopping its movements after 1 equiv of chloride is added. Protons Hh and Hi have inflection

• fitting of 1H NMR titration data. Both software have their limitations but their usage as tools to unravel complex equilibria is without parallel. Cooperativity of ion–pair complexation The most recent undertaking of ion pairing is to make it a feature and to examine, in glorious detail, how ion pairs can

Smart molecules for imaging, sensing and health (SMITH)

• Bradley D. Smith

Beilstein J. Org. Chem. 2015, 11, 2540–2548, doi:10.3762/bjoc.11.274

• awareness of the need for transport carrier molecules that could simultaneously complex both the anion and the cation [24][25]. Starting in 2000 we prepared a number of relatively simple macrobicyclic receptors that could bind salts as either contact ion-pairs or as solvent separated ion-pairs [26][27][28

• author as director of the Notre Dame Integrated Imaging Facility. Chronological progression of Smith group research projects. Molecular transporters promote translocation of ions or hydrophilic biomolecules across a synthetic or biological membrane. Macrocyclic receptor that binds solvent separated ion

• -pairs. Trapping a macrocyclic receptor containing a reactive ion-pair produces an interlocked [2]rotaxane. (top) Basis of Synthavidin technology. A fluorescent squaraine dye that is flanked by PEG chains can rapidly thread a tetralactam macrocycle in water to produce a highly stable complex. (bottom

Bis(vinylenedithio)tetrathiafulvalene analogues of BEDT-TTF

• Erdal Ertas,
• İlknur Demirtas and
• Turan Ozturk

Beilstein J. Org. Chem. 2015, 11, 403–415, doi:10.3762/bjoc.11.46

• thickness of the film was obtained. The film was annealed at 25, 55, 85, 115 and finally at 145 °C for 30 min. Electronic transitions of the complex 54, i.e. n–π* and π–π* transitions, led to the formation of radical ion pairs 55. The refractive index dispersion and optical constant of the annealed film

Microsolvation and sp²-stereoinversion of monomeric α-(2,6-di-tert-butylphenyl)vinyllithium as measured by NMR

• Rudolf Knorr,
• Monika Knittl and
• Eva C. Rossmann

Beilstein J. Org. Chem. 2014, 10, 2521–2530, doi:10.3762/bjoc.10.263

• trans) through a “diastereotopomerization” [23] that interconverts the ground-state contact-ion pairs (CIP) 11 and 11' in Scheme 3. Increasing rates of this interchange will cause at first an increasing line broadening of the AB system and then a “coalescence” of all four lines into a singlet at the

Macrocyclic bis(ureas) as ligands for anion complexation

• Claudia Kretschmer,
• Gertrud Dittmann and
• Johannes Beck

Beilstein J. Org. Chem. 2014, 10, 1834–1839, doi:10.3762/bjoc.10.193

• DMSO itself is bound to the urea functional groups (Figure 1). If an excess of NEt4Br is added to a solution of 2 in DMSO, on slow evaporation yellow crystals of NEt4[Br·2] are separated. The crystal structure consists of ion pairs, tetraethylammonium cations and bromide anions, which are located in

A study on electrospray mass spectrometry of fullerenol C₆₀(OH)₂₄

• Mihaela Silion,
• Andrei Dascalu,
• Mariana Pinteala,
• Bogdan C. Simionescu and
• Cezar Ungurenasu

Beilstein J. Org. Chem. 2013, 9, 1285–1295, doi:10.3762/bjoc.9.145

• + H]+ and deprotonated [M − H]− molecules, and distonic deprotonated molecules for those identified from a deprotonated molecule plus loss of HO• and/or H• radicals [M − HO• − H• − H]−. However, while only radical-ion pairs have been identified by ESI-MS as distonic ions, the distonic deprotonated

Synthesis of guanidinium–sulfonimide ion pairs: towards novel ionic liquid crystals

• Martin Butschies,
• Manuel M. Neidhardt,
• Markus Mansueto,
• Sabine Laschat and
• Stefan Tussetschläger

Beilstein J. Org. Chem. 2013, 9, 1093–1101, doi:10.3762/bjoc.9.121

• complementary ion pairs, consisting of both, mesogenic cation and anion, was extended from guanidinium sulfonates to guanidinium sulfonimides. In this preliminary study, the synthesis and mesomorphic properties of selected derivatives were described, which provide the first example of an ILC with the

• sulfonimide anion directly attached to the mesogenic unit. Keywords: anion exchange; ionic liquid crystals; ion pairs; mesophases; sulfonimides; Introduction While ionic liquids, i.e., molten salts composed of either organic cation or anion (or both) with melting points far below 100 °C, are extensively

• ][18][19]. By using an elongated perfluoroalkyl chain at the bistriflimide anion in combination with short chain-substituted pyrrolidinium cations MacFarlane was able to induce plastic crystal phases and liquid-crystalline phases at room temperature [20]. Ion pairs consisting of perfluorosulfonylimide

Electron and hydrogen self-exchange of free radicals of sterically hindered tertiary aliphatic amines investigated by photo-CIDNP

• Martin Goez,
• Isabell Frisch and
• Ingo Sartorius

Beilstein J. Org. Chem. 2013, 9, 437–446, doi:10.3762/bjoc.9.46

• reaction occurs through successive radical pairs. With AQ, the polarizations stem from the initially formed radical-ion pairs, and escaping DH•+ then undergoes electron self-exchange with DH. In the reaction sensitized with XA (or BP), the polarizations arise in a secondary pair of neutral radicals that is

• polarizations. When escape predominates, all polarizations originate from the radical-ion pairs, when the in-cage deprotonation prevails, from the pairs of neutral radicals. Because the rate of in-cage deprotonation depends on the free energy of that reaction ∆Gdep, a threshold behaviour is observed: For

• representatives that yield CIDNP from the radical-ion pairs and from the pairs of neutral radicals, respectively. Owing to competing side-reactions, kinetic studies were not feasible with triethylamine, but for the two amines of this work, they are. As we will show, depending on the sensitizer, different spin

Inter- and intramolecular enantioselective carbolithiation reactions

• Asier Gómez-SanJuan,
• Nuria Sotomayor and
• Esther Lete

Beilstein J. Org. Chem. 2013, 9, 313–322, doi:10.3762/bjoc.9.36

• using DMPU as an additive to accelerate the aryl migration [17], probably by favoring the formation of solvated ion pairs [18]. Thus, this tandem enantioselective carbolithiation–rearrangement of vinylic ureas bearing an N-aryl group leads to the formation of two new carbon–carbon bonds with control of

Aromatic and heterocyclic perfluoroalkyl sulfides. Methods of preparation

• Vladimir N. Boiko

Beilstein J. Org. Chem. 2010, 6, 880–921, doi:10.3762/bjoc.6.88

• groups to stabilize the mercapto-radicals in the radical ion pairs [•O2NArS + RF−] and [•O=CArS + RF−]. As a result, these radicals are less reactive, although at higher temperatures an increase in their activity is observed. The participation of radicals is supported by the fact that the addition of

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

• energies are between 42 and 92 kJ/mol in the gas phase. The cation–π-bond is an important motif for the recognition of quaternary ammonium ions. A relevant example is the binding of acetylcholine (3) in biological systems [13]. 3) Ion pairs and salt bridges Coulombic interaction attracts cations and anions

Self-association of an indole based guanidinium-carboxylate-zwitterion: formation of stable dimers in solution and the solid state

• Carolin Rether,
• Wilhelm Sicking,
• Roland Boese and
• Carsten Schmuck

Beilstein J. Org. Chem. 2010, 6, No. 3, doi:10.3762/bjoc.6.3

• , 45141 Essen, Germany 10.3762/bjoc.6.3 Abstract The indole based zwitterion 2 forms stable dimers held together by H-bond assisted ion pairs. Dimerisation was confirmed in the solid state and studied in solution using dilution NMR experiments. Even though zwitterion 2 forms very stable dimers even in

• due to the −M effect of the carbonyl group or the aromatic ring, respectively, thus facilitating the formation of H-bond assisted ion pairs [18][19]. Apart from the increased acidity of the NHs in 1 and 2, also the geometric shape of 2 is very similar to 1 at least based on the inspection of simple

• geometry of the H-bonded ion pairs and reflects the importance of planarity in zwitterion 1 for an effective dimerisation. Due to the twisted guanidinium groups in 2 the two monomers in dimer 2·2 are not in-plane, which leads to less efficient interactions. Also as mentioned above, the guanidinium group in

Synthesis and redox behavior of new ferrocene- π-extended- dithiafulvalenes: An approach for anticipated organic conductors

• Abdelwareth A. O. Sarhan,
• Omar F. Mohammed and
• Taeko Izumi

Beilstein J. Org. Chem. 2009, 5, No. 6, doi:10.3762/bjoc.5.6

• , respectively. From this study we can estimate the timescales of the charge separation and recombination of the produced radical ion pairs. Such laser spectroscopic studies will have a big impact in future, leading not only new synthetic applications, but also to the discovery of new photophysical properties of