Design and synthesis of a bis-macrocyclic host and guests as building blocks for small molecular knots

• Elizabeth A. Margolis,
• Rebecca J. Keyes,
• Stephen D. Lockey IV and
• Edward E. Fenlon

Beilstein J. Org. Chem. 2020, 16, 2314–2321, doi:10.3762/bjoc.16.192

• on cryptands [2], and Cram on hemicarcerands [3] demonstrated that preorganized macrocycles have the ability to act as hosts for various guest cations and compounds. Their seminal work was recognized with the 1987 Nobel Prize in Chemistry. More recently, the 2016 Nobel Prize in Chemistry was won by

• Da, [M + H]+, 88; 1584.9 Da, [M + Na]+, 28; 1601.9 Da, [M + K]+, 52; 1626.8 Da, [M + Cu]+, 42. It is not surprising that the product would sequester metal cations given its electron-rich macrocyclic nature. Of course, the mass spectral data do not address whether the unknot, trefoil knot, or both

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

• sensory material for selective recognition of cesium cations in water. In another event, Hirao’s group has prepared trioxosumanene 40 in the presence of RuCl3 and t-BuO2H which could be used as a key building block to generate diverse significant electroactive materials by virtue of nucleophilic addition

• by virtue of ROM–RCM which on subsequent DDQ oxidation followed by HWE reaction provided the desired compound 108 (Scheme 26). In a really brilliant manner, Kasprzak and Sakurai in 2019 have created a sumanene–ferrocene dual system for selective recognition of cesium cations by means of site

• were treated with tert-butyl hydroperoxide (TBHP), two flanking benzene rings were found to be cleaved to afford 174 and 175 in impressive yields (Scheme 45) [82][83][84]. Moreover, they observed radical cations 172 and 173 formation when the same compounds were reacted with Br2 or 2,3,5,6-tetrafluoro

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

• Shahboz Yakubov and
• Joshua P. Barham

Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183

• been responsible for generating more Selectfluor®-derived radical cations that drove the reaction towards difluorination to afford the product 28a. However, it is important to note that only difluorinated products were detected and no monofluorinated products were observed, regardless of whether

• [201], due to the instability of the primary radical (Figure 10). The selective fluorination of C2 over C3 may be rationalized by steric effects (rather than polarity matching), which are reported for quinuclidinium radical cations [203]. A similar selectivity for the most hydridic C(sp3)–H bond was

Naphthalene diimide–amino acid conjugates as novel fluorimetric and CD probes for differentiation between ds-DNA and ds-RNA

• Annike Weißenstein,
• Myroslav O. Vysotsky,
• Ivo Piantanida and
• Frank Würthner

Beilstein J. Org. Chem. 2020, 16, 2032–2045, doi:10.3762/bjoc.16.170

• cations and water molecules from the DNA/RNA grooves [44][45] by side arms interacting with the grooves and thereby supporting the binding. Circular dichroism experiments CD spectroscopy is an ideal method to get insight into the changes of the polynucleotide secondary structure upon binding of small

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

• attractive approach to tackle this central challenge [1][2][3][11][12][13][14]. The noncovalent interaction between the guanidinium cations from CPPs and cell membrane-associated anions, such as phospholipids, proteoglycans, or sialic acids, is considered to enhance the cell surface accumulation of

• )pyrrole (GCP) cation 1 as a synthetic analogue of the guanidinium cations, somehow a “super-guanidinium” conceived to drive “arginine magic” [20][21] to the extreme (Figure 1) [23]. The power of the Schmuck cation to bind carboxylate and phosphate anions in competitive water has several origins [22

• ]. 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

Design, synthesis and application of carbazole macrocycles in anion sensors

• Alo Rüütel,
• Ville Yrjänä,
• Sandip A. Kadam,
• Indrek Saar,
• Mihkel Ilisson,
• Astrid Darnell,
• Kristjan Haav,
• Tõiv Haljasorg,
• Lauri Toom,
• Johan Bobacka and
• Ivo Leito

Beilstein J. Org. Chem. 2020, 16, 1901–1914, doi:10.3762/bjoc.16.157

• matrix. Permselectivity is conferred to the polymeric membrane by the addition of an ion exchanger, which is a lipophilic ion, and an ionophore. The ion exchanger provides permselectivity for anions or cations depending on whether the ion exchanger salt contains a lipophilic cation or anion, respectively

Natural dolomitic limestone-catalyzed synthesis of benzimidazoles, dihydropyrimidinones, and highly substituted pyridines under ultrasound irradiation

• Kumar Godugu,
• Venkata Divya Sri Yadala,
• Mohammad Khaja Mohinuddin Pinjari,
• Trivikram Reddy Gundala,
• Lakshmi Reddy Sanapareddy and
• Chinna Gangi Reddy Nallagondu

Beilstein J. Org. Chem. 2020, 16, 1881–1900, doi:10.3762/bjoc.16.156

• ) within 10 min (Table 5, entry 8). The reaction was expected to proceed through the activation of the carbonyl group of 2h (of which 2.0 mmol were used) by the cations (Ca2+ and Mg2+, respectively) of the NDL. This was followed by a nucleophilic attack of the NH2 groups of o-phenylenediamine (1, of which

One-pot synthesis of isosorbide from cellulose or lignocellulosic biomass: a challenge?

• Isaline Bonnin,
• Raphaël Mereau,
• Thierry Tassaing and
• Karine De Oliveira Vigier

Beilstein J. Org. Chem. 2020, 16, 1713–1721, doi:10.3762/bjoc.16.143

• are used with low concentration, a reduced salt will be formed after the neutralization step. Moreover, heteropolyacids can be precipitated via ion exchange with larger cations, e.g., K+, Cs+ and NH4+, or in certain cases even extracted to allow direct recycling. Thus, the usage of heterogeneous acid

Rearrangement of o-(pivaloylaminomethyl)benzaldehydes: an experimental and computational study

• Csilla Hargitai,
• Györgyi Koványi-Lax,
• Tamás Nagy,
• Péter Ábrányi-Balogh,
• András Dancsó,
• Gábor Tóth,
• Judit Halász,
• Angéla Pandur,
• Gyula Simig and
• Balázs Volk

Beilstein J. Org. Chem. 2020, 16, 1636–1648, doi:10.3762/bjoc.16.136

• explained by the protonation of ring tautomers 9 to 10 (Scheme 4), followed by a water elimination, and subsequent deprotonation of cations 11 to afford isoindoles 4 [3][4][5]. The protonation of the latter [6], followed by the attack of water at position 1 of cations 12, and subsequent deprotonation of

• formation of the dimer-like products 3a and 3b can be rationalized by the electrophilic attack of cations 12a,b at position 3 of isoindoles 4a,b to give cations 15a,b (Scheme 5). The reaction of the latter with water, followed by deprotonation leads to dimer-like compounds 16a,b, being the ring tautomers of

• the isolated products 3a and 3b. On the contrary, the formation of dimer-like products 8a and 8b can be explained by the electrophilic attack of cations 11c,d at position 1 (instead of position 3) of isoindoles 4c,d to afford cations 17a,b (Scheme 6), which transform to the dimer-like products 5a,b

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

• the rate of recombination [91]. The abrupt termination of an ordered lattice continuity at a surface leads to chemical and structural differences from the bulk material. TiO2, for example, has surface hydroxides, oxygen anions, and Ti3+ cations, which produce high energy states from incomplete bonding

Activated carbon as catalyst support: precursors, preparation, modification and characterization

• Melanie Iwanow,
• Tobias Gärtner,
• Volker Sieber and
• Burkhard König

Beilstein J. Org. Chem. 2020, 16, 1188–1202, doi:10.3762/bjoc.16.104

• . Poly(propiolate) salts are formed by polymerization of the starting materials after heating. The different cations of the propiolates cause changes in the thermal behavior of the starting materials since different temperatures are required for the decomposition or different amounts of gases are

• starting materials. The thermal decomposition behavior of the precursors, and thus the resulting morphology of the carbon materials is influenced by the propiolate cations [80]. Spherical carbons The preparation of spherical mesoporous carbon particles as catalyst support with high surface areas

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• cations and radical anions) Recently, the exploitation of alkenyl and aryl radical ions has emerged as a platform for the functionalization of small molecules. They appear as attractive intermediates for a direct alkene difunctionalization or arene C–H functionalization. In particular, radical cations are

• class of substrates that usually undergo a protonation to form C(sp3) radicals. Alkenyl or aryl radical ions are generally accessed through SET. The presence of electron-donating groups facilitates the oxidation of the precursor to the radical cations, while electron-poor alkynes and arenes can undergo

• , exploiting the reactivity of alkene radical cations generated using organic dyes [96][97]. Their seminal work reported the oxidation of the alkenols 22.1 by the Fukuzumi dye (OD2, Scheme 22) [98]. The so-formed radical cation undergoes an intramolecular nucleophilic 5/6/7-exo-trig-cyclization to give the

The charge-assisted hydrogen-bonded organic framework (CAHOF) self-assembled from the conjugated acid of tetrakis(4-aminophenyl)methane and 2,6-naphthalenedisulfonate as a new class of recyclable Brønsted acid catalysts

• Svetlana A. Kuznetsova,
• Alexander S. Gak,
• Yulia V. Nelyubina,
• Vladimir A. Larionov,
• Han Li,
• Michael North,
• Vladimir P. Zhereb,
• Alexander F. Smol'yakov,
• Artem O. Dmitrienko,
• Michael G. Medvedev,
• Igor S. Gerasimov,
• Ashot S. Saghyan and
• Yuri N. Belokon

Beilstein J. Org. Chem. 2020, 16, 1124–1134, doi:10.3762/bjoc.16.99

• , elemental analysis, and 1H NMR spectroscopy. The framework was supported by hydrogen bonds between the sulfonate anions and the ammonium cations of NDS and protonated TAPM moieties, respectively. The CAHOF material functioned as a new type of catalytically active Brønsted acid in a series of reactions

• -assisted hydrogen-bonded framework (CAHOF), as was the case when multitopic guanidinium or amidinium cations were combined with polycarboxylates, polysulfonates, or polyphosphonates [30][31][32][33]. The synthesis of a HOF or CAHOF consists of simply mixing the two components together [29]. An additional

• parameters a = 20.6034(8) Å, b = 20.1330(8) Å, c = 22.4357(8) Å, β = 91.989(1)°, and cell volume = 9300.9(6) Å3 at 120 K. An asymmetric part of the unit cell contained two ammonium cations, four sulfonate anions, and nine water molecules, held together by numerous hydrogen bonds (Table S2, Supporting

Cation-induced ring-opening and oxidation reaction of photoreluctant spirooxazine–quinolizinium conjugates

• Phil M. Pithan,
• Sören Steup and
• Heiko Ihmels

Beilstein J. Org. Chem. 2020, 16, 904–916, doi:10.3762/bjoc.16.82

• ., 1aSO: λabs = 317 nm, 1aMC: λabs = 602 nm, in MeCN) [16]. In some instances, the ring-opening reaction may also be induced in the dark through the addition of particular metal cations that are able to coordinate to the phenolate oxygen atom and/or other additional coordinating atoms and substituents

• that have been introduced into the structure of the spirooxazine and spiropyran derivatives [17][18][19][20][21][22][23][24][25][26]. Regardless of whether the ring-opening reaction is induced by cations or irradiation, the coordination of metal ions to the substrate usually results in a negative

• photochromism, i.e., a blue shift of the absorption maximum of the merocyanine form [5][19][27][28][29], and increased stability of the latter towards the thermal back reaction [21][28][30][31][32][33][34]. In this context, the complexation of metal cations has also been exploited to utilize this compound class

Rhodium-catalyzed reductive carbonylation of aryl iodides to arylaldehydes with syngas

• Zhenghui Liu,
• Peng Wang,
• Zhenzhong Yan,
• Suqing Chen,
• Dongkun Yu,
• Xinhui Zhao and
• Tiancheng Mu

Beilstein J. Org. Chem. 2020, 16, 645–656, doi:10.3762/bjoc.16.61

• direct coupling products (namely, benzene and biphenyl) were detected as the main byproducts by GC–MS. This observation also explains why the conversions were always higher than the yields. Effects of ligands Ligands play a decisive role in adjusting the catalytic ability of metal cations [12][13][41][42

• ][43][44][45][46][47][48][49][50][51]. Different ligands coordinating with the same metal cations could make a difference between full conversion with nearly quantitative yields and no reactions. To obtain the optimized conditions, 13 kinds of ligands were tested and their structures are included in

Regio- and stereoselective synthesis of new ensembles of diversely functionalized 1,3-thiaselenol-2-ylmethyl selenides by a double rearrangement reaction

• Svetlana V. Amosova,
• Andrey A. Filippov,
• Nataliya A. Makhaeva,
• Alexander I. Albanov and
• Vladimir A. Potapov

Beilstein J. Org. Chem. 2020, 16, 515–523, doi:10.3762/bjoc.16.47

• thiiranium 3 cations, whose participation in the nucleophilic substitution reaction will lead to two different reaction products (Scheme 1). However, particularly, the reaction proceeds via an intermediate seleniranium cation 2. This is explained by the high anchimeric assistance effect of the selenium atom

• was developed during the last ten years based on new directions for nucleophilic substitution reactions proceeding via intermediate seleniranium cations 2 generated from thiaselenole 1. We have carried out new regioselective reactions of thiaselenole 1 with dithiocarbamates [31], ketones [37], thiols

• chemistry. Monitoring the reaction of thiaselenole 1 with KSeCN by 1H NMR spectroscopy (in accordance with the data of Table 1). Reaction conditions: compound 1 (0.5 mmol), KSeCN (0.5 mmol), MeCN (2.5 mL), 0 °C. Possible formation of reaction products starting from 1 via seleniranium 2 or thiiranium cations

Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0

• Bernd Strehmel,
• Christian Schmitz,
• Ceren Kütahya,
• Yulian Pang,
• Anke Drewitz and
• Heinz Mustroph

Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40

Oligomeric ricinoleic acid preparation promoted by an efficient and recoverable Brønsted acidic ionic liquid

• Fei You,
• Xing He,
• Song Gao,
• Hong-Ru Li and
• Liang-Nian He

Beilstein J. Org. Chem. 2020, 16, 351–361, doi:10.3762/bjoc.16.34

• , entries 1–4 vs 5), which may originate from its higher proton concentration in the reaction system. With H2PO4− as anion, the ILs containing different cations were then synthesized and their catalytic activity on the esterification reaction was investigated. The results (Table 1, entries 5–9) revealed

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• cations, polyoxometallates, and benzophenones [9][80], but a major drawback is the limited availability of photocatalysts that can perform direct HAT. Therefore, there is a high demand for a direct-HAT catalyst that is accessible, metal-free, allows no side reactions, and can be activated by visible light

• flash photolysis measurements, and the monobrominated product selectivity was controlled by the difference in electron transfer oxidation reactivity of 127 and 126 of electron transfer state of photocatalyst (Me·+ moiety) and also on the radical cations reactivity with Br−. Recently, König’s group

Halogen-bonding-induced diverse aggregation of 4,5-diiodo-1,2,3-triazolium salts with different anions

• Xingyu Xu,
• Shiqing Huang,
• Zengyu Zhang,
• Lei Cao and
• Xiaoyu Yan

Beilstein J. Org. Chem. 2020, 16, 78–87, doi:10.3762/bjoc.16.10

• (3)°, 144.12(7)° and 145.6(3)°. The crystal X-ray analyses of 2-BF4 shows that the diiodotriazolium moiety has formed with the tetrafluoroborate anion a triangle in which only two anions and three cations are assembled and one tetrafluoroborate is independent (Figure 3). 2-BF4 crystallizes in the

• values are 0.72 and 0.73. The single crystal of 2-TFA crystallizes in the monoclinic space group P21/n, but the packing structure of 2-TFA is different. The package diagram shows that two cations and two acetates form a boat shape (Figure 5). The C–I···O distances are 2.631(8) Å, 2.739(8) Å, 2.666(6) Å

Understanding the role of active site residues in CotB2 catalysis using a cluster model

• Keren Raz,
• Ronja Driller,
• Thomas Brück,
• Bernhard Loll and
• Dan T. Major

Beilstein J. Org. Chem. 2020, 16, 50–59, doi:10.3762/bjoc.16.7

• non-interacting residues are labeled in grey, and plus signs note location of the cations. TS structures TS_A_B–TS_G/H_I in the active site model. Interactions are marked by dashed orange lines, the interacting residues are labeled in black, the non-interacting residues are labeled in grey, and the

• plus signs note the location of the cations. Comparison between gas phase and active site model conformations. A) Intermediate D. B) Intermediate E. Mechanism for formation of cyclooctat-9-en-7-ol, published similarly in [42]. Interactions between intermediates and TS structures with active site

Extension of the 5-alkynyluridine side chain via C–C-bond formation in modified organometallic nucleosides using the Nicholas reaction

• Renata Kaczmarek,
• Dariusz Korczyński,
• James R. Green and
• Roman Dembinski

Beilstein J. Org. Chem. 2020, 16, 1–8, doi:10.3762/bjoc.16.1

• material containing the propargyl alcohol derivative unit. The chemistry of cationic propargyl dicobalt complexes, recognized as the Nicholas reaction, has become one of the most widely appreciated forms of metalorganic chemistry. These cations are generated most commonly from propargyl alcohol, -ether, or

Bacterial terpene biosynthesis: challenges and opportunities for pathway engineering

• Eric J. N. Helfrich,
• Geng-Min Lin,
• Christopher A. Voigt and
• Jon Clardy

Beilstein J. Org. Chem. 2019, 15, 2889–2906, doi:10.3762/bjoc.15.283

• cyclization reactions. Textbook TCs are categorized into two classes and differ in their mechanisms of substrate activation as well as their protein folds [37][50][51][52]. Type I TCs trigger the formation of highly reactive allylic cations by heterolytic cleavage of the terminal pyrophosphate of farnesyl

Preparation of anthracene-based tetraperimidine hexafluorophosphate and selective recognition of chromium(III) ions

• Qing-Xiang Liu,
• Feng Yang,
• Zhi-Xiang Zhao,
• Shao-Cong Yu and
• Yue Ding

Beilstein J. Org. Chem. 2019, 15, 2847–2855, doi:10.3762/bjoc.15.278

• hydrogen bonds, namely C(3)–H(3A)···F(2) and C(17)–H(17A)···F(2) interactions (Supporting Information File 1, Figure S1b). Chemosensing of cations by 3 Compound 3 was employed as a host to study its ability to detect some cations through fluorescence and UV titrations in CH3CN/DMSO, 9:1, v/v at room

• ) did not exhibit any remarkable response to the addition of these cations, except for Cr3+ (ε = 1.1⋅104 mol−1⋅dm3⋅cm−1) as a result of 3·Cr3+ formation (Supporting Information File 1, Figure S2). These results show that 3 is able to effectively distinguish Cr3+ from other cations. To further

• Cr3+ selectively while neglecting other cations, with no remarkable interference being caused in the presence of the latter. In order to probe whether the anions of the chromium(III) salts had effects on the binding of 3 and Cr3+, other chromium(III) salts, CrCl3, CrBr3, Cr2(SO4)3, Cr(NO3)3, and Cr

A chiral self-sorting photoresponsive coordination cage based on overcrowded alkenes

• Constantin Stuckhardt,
• Diederik Roke,
• Wojciech Danowski,
• Edwin Otten,
• Sander J. Wezenberg and
• Ben L. Feringa

Beilstein J. Org. Chem. 2019, 15, 2767–2773, doi:10.3762/bjoc.15.268

• by using the Stokes–Einstein equation [54]. By means of ESI high-resolution mass spectrometry, we were able to verify the Pd2L4 constitution of both cages. The HRMS spectrum of Pd2(stable Z-1)4 shows the signals for the cations [Pd2(stable Z-1)4(NO3)3]+, [Pd2(stable Z-1)4(NO3)2]2+, [Pd2(stable Z-1)4

• (NO3)]3+, [Pd2(stable Z-1)4]4+ (Figure 3). For Pd2(stable E-1)4, the peaks corresponding to the cations [Pd2(stable E-1)4(NO3)2]2+ and [Pd2(stable E-1)4(NO3)]3+ were observed (Figure 3). For both isomers, the experimental isotopic patterns and exact m/z values match the simulated patterns. A single