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

• between the catechol ring of the crown ether and aromatic moieties of the secondary ammonium ion contribute to the complex formation [22][23][24][25]. Over the last 25 years, a detailed understanding of the thermodynamic and kinetic properties of crown ether/ammonium complexes has developed enabling the

• stronger complexes with secondary ammonium ions than the larger analog. But since phenyl groups already act as a stopper for BC7, one side of the ammonium axle must be an alkyl chain, as in A2·PF6 to enable pseudo[2]rotaxane formation (Figure 1c) [45][46]. The smaller TTF-containing crown ethers TTFC7 and

• is impeded. NDIC8 therefore does not fold but stacks with the naphthalene and NDI moieties of the neighbors alternatingly in the solid state and with a typical plane/plane distance of 3.57 Å [49]. Thermodynamic analysis of crown ether/ammonium complexes For the investigation of the thermodynamic

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

• -fullerene in co-organic solvents and aqueous solution was investigated by fluorescence spectroscopy and ultraviolet-visible spectroscopy. The association stoichiometry of the complexes TBTQ-(OG)6 with C60 and TBTQ-(OG)6 with C70 was found to be 1:1 with binding constants of Ka = (1.50 ± 0.10) × 105 M−1 and

• derivatives with fullerenes has been limited to organic media so far because of the poor solubility of their complexes in aqueous media. Therefore, the design, synthesis, and exploration of water-soluble TBTQ derivatives offer attractive possibilities for broadening the applications of the TBTQ structural

• -fullerenes precipitated rapidly within 5 min. In contrast, the TBTQ-(OG)6 C60 and TBTQ-(OG)6 C70 complexes showed improved water dispersibility of the fullerenes, which was maintained even after 20 days. The maximum solubility of C60 in water was measured to be about 0.14 mg/mL in the presence of ten

NMR Spectroscopy of supramolecular chemistry on protein surfaces

• Peter Bayer,
• Anja Matena and
• Christine Beuck

Beilstein J. Org. Chem. 2020, 16, 2505–2522, doi:10.3762/bjoc.16.203

• ], guanidiniocarbonylpyrrole (GCP) ligands [41][42][43][44][45][46], cucurbiturils [47][48][49][50][51], porphyrins [52][53][54][55][56][57][58][59][60], metal complexes [61][62][63], foldamers [64][65][66][67], nanoparticles [34][68], imprinted polymers [69][70][71][72], and dendrimers [73][74]. In this review, we focus

• protein multimerization [60], and have shown antiviral properties [58]. Metal complexes, such as RuII(bpy)3 complexes, have been designed as protein surface mimetics to target charged areas on protein surfaces [61][62][63]. The ligand sphere of the metal can be modified to recognize either positively or

• ). However, this requires knowledge of the chemical shifts and relaxation rates for both, the free and bound components in pure form, which are challenging to obtain for complexes with only moderate affinity. For example, the binding of a single GCP unit to the carboxylates of different N-acetylated amino

Computational tools for drawing, building and displaying carbohydrates: a visual guide

• Kanhaya Lal,
• Rafael Bermeo and
• Serge Perez

Beilstein J. Org. Chem. 2020, 16, 2448–2468, doi:10.3762/bjoc.16.199

• form of images [13][14]. Besides, these tools for representing glycans in 2D and 3D shape [15] allowed the integration of glycans into protein structures or complexes. The tools developed in the last few years have automated the sketching of glycans and glycopeptides, allowing rapid display of

• hand, the Glycan Modeler allows in silico N-/O-glycosylation for glycan-protein complexes and generates a “most relevant” glycan structure through Glycan Fragment Database (GFDB) [68] search which gives proper orientations relative to the target protein. In the absence of target glycan sequence in GFDB

Catalytic trifluoromethylation of iodoarenes by use of 2-trifluoromethylated benzimidazoline as trifluoromethylating reagent

• Tatsuhiro Uchikura,
• Nanami Kamiyama,
• Taisuke Ishikawa and
• Takahiko Akiyama

Beilstein J. Org. Chem. 2020, 16, 2442–2447, doi:10.3762/bjoc.16.198

• ; catalysis; copper; fluorine chemistry; trifluoromethylation; Introduction The introduction of a trifluoromethyl group is one of the most attractive reactions in drug discovery [1][2]. In the past decade, trifluoromethylation reactions of aryl halides in the presence of transition-metal complexes were

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• followed by a separate enantioselective catalysis step that will not be covered in this review [17][18][19]. Examples using cage complexes or other supramolecular reagents also lie outside the scope of this review. As all enantioselective photocatalysis requires a secondary mode of catalysis to induce

• by Bach to the deracemisation of allenes rac-194 (Scheme 29) [85]. The proposed mechanism proceeds through configurationally isomeric hydrogen bonding complexes 195 and 195’, with subsequent photoexcitation of the thioxanthone chromophore leading to racemisation of the allene through a triplet state

• desired products 267 or 268 in moderate yields and enantioselectivities (3 examples, up to 75:25 er for 267 and 2 examples, up to 68:32 er for 268). Lewis acid catalysis Lewis acids have been known for decades to activate carbonyl compounds through the formation of coordination complexes that increases

Hierarchically assembled helicates as reaction platform – from stoichiometric Diels–Alder reactions to enamine catalysis

• David Van Craen,
• Jenny Begall,
• Johannes Großkurth,
• Leonard Himmel,
• Oliver Linnenberg,
• Elisabeth Isaak and
• Markus Albrecht

Beilstein J. Org. Chem. 2020, 16, 2338–2345, doi:10.3762/bjoc.16.195

• addition of chiral ammonium salts leads to the preference of a specific twist at the helicate [32]. As inductor, (R)-1-phenylethylammonium chloride was added to the racemic hexadiene-substituted helicate [Li3(1)6Ti2]−. The chiral salt influences the helicity of the monomeric complexes and which dimerize to

• statistical ligand distribution Li[Li3(1)3(L*)3Ti2] (L* = 3–7-H2). The given formula only describes the ratio of the ligands but in fact a statistical mixture of complexes Li[Li3(L*)6Ti2], Li[Li3(1)(L*)5Ti2], Li[Li3(1)2(L*)4Ti2], Li[Li3(1)3(L*)3Ti2], Li[Li3(1)4(L*)2Ti2], Li[Li3(1)5(L*)1Ti2], and Li[Li3(1)6Ti2

• the supposed reason for this observation. Thus, the amine ligand 13b-H2 seemed to be an appropriate component to make helicates from ligand mixtures which possess catalytic activity. Exchange of the chiral ligand 2 by other chiral ones resulted in the corresponding complexes Li4[(13b)1(4)5Ti2] and Li4

Host–guest interaction of cucurbit[8]uril with oroxin A and its effect on the properties of oroxin A

• Zhishu Zeng,
• Jun Xie,
• Guangyan Luo,
• Zhu Tao and
• Qianjun Zhang

Beilstein J. Org. Chem. 2020, 16, 2332–2337, doi:10.3762/bjoc.16.194

• ][2][3]. As a consequence of the specific structural features of Q[n]s, which have two hydrophilic “portals” decorated with partially negatively charged carbonyl groups and a hydrophobic cavity [4], cucurbit[n]urils are able to form host–guest complexes with a range of drugs [5][6][7]. These complexes

Synthesis of 1,4-benzothiazinones from acylpyruvic acids or furan-2,3-diones and o-aminothiophenol

• Ekaterina E. Stepanova,
• Maksim V. Dmitriev and
• Andrey N. Maslivets

Beilstein J. Org. Chem. 2020, 16, 2322–2331, doi:10.3762/bjoc.16.193

• potential Cu2+ chemosensors [14], and their BF2 chelates, as multicolor fluorescence complexes, some of which exhibited aggregation-induced emission (AIE) properties [15]. In addition, enaminones I and II proved themselves to be versatile and available building blocks for the synthesis of various

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

• , since its first successful synthesis, a variety of functionalized sumanenes as well as heterosumanenes have been developed because of their unique physiochemical properties. For example, bowl-to-bowl inversion, bowl depth, facial selectivity, crystal packing, metal complexes, intermolecular charge

• -anion exchange with hexafluorophosphate (Scheme 30) [61]. Two years later to this report, the same group has also reported the synthesis of complexes 123b and 123c under almost similar reaction conditions [62]. On the other occasion, they have also prepared the tri- and mononuclear sumanenyl zirconocene

• complexes 124 and 125, respectively, as displayed in Scheme 31 [63]. The mono-zirconocene complex 125 was arranged by treating sumanene (2) with 1 equivalent of n-BuLi in THF-d8 to generate the monoanion at the benzylic position which on further treatment with CpZrCl3 provided the mono-zirconocene complex

Naphthalene diimide bis-guanidinio-carbonyl-pyrrole as a pH-switchable threading DNA intercalator

• Poulami Jana,
• Filip Šupljika,
• Carsten Schmuck and
• Ivo Piantanida

Beilstein J. Org. Chem. 2020, 16, 2201–2211, doi:10.3762/bjoc.16.185

• intercalators, particularly those which have substituents protruding into either the major or minor grooves (or both) [29]. For a more detailed structural analysis of the complexes, CD spectroscopy was applied [12][13]. It should be noted that due to the distance between the asymmetric atom and NDI or GCP

• for Ka and n given in Table 1 all have satisfactory correlation coefficients (>0.999). Thermal melting curves for DNA, RNA, and their complexes with the studied compound were determined as previously described [37] by following the absorption change at 260 nm as a function of temperature. The

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

• of aryl triflates [29] and arylpalladium complexes [2][47], few permit a one-step transformation of unactivated C(sp3)–H bonds to C(sp3)–F bonds [1][3][36][38][48]. Such a transformation would be highly valuable for the late-stage functionalization (LSF) of complex molecules, such as those in Scheme

• byproducts. It is inexpensive, sustainable (ideally not ruthenium or iridium complexes) and commercially available. Due to their comparatively high triplet energies and the long lifetime of their triplet states; organic dyes and various ruthenium and iridium complexes are well-suited photosensitizers [118

• , triplet state energies and lifetimes of several small organic molecule/dye PSCats. Figure 7 shows the corresponding information for selected prototypical transition metal complexes. 2.2 Fluorination reagents An extensive discussion on the different types of fluorination reagents is beyond the scope of

Efficient [(NHC)Au(NTf₂)]-catalyzed hydrohydrazidation of terminal and internal alkynes

• Maximillian Heidrich and
• Herbert Plenio

Beilstein J. Org. Chem. 2020, 16, 2080–2086, doi:10.3762/bjoc.16.175

• ; Introduction Cationic gold complexes with weakly coordinating counterions (which are often considered to be solvent-separated ions) [1][2][3], render powerful catalysts for the transformation of organic substrates [4][5][6], specifically the reactions of alkynes with a variety of heteroatom nucleophiles

• activity of gold complexes in such reactions tends to be higher, when using sterically demanding ligands (NHC, phosphine) [41]. Recently, the hydrohydrazidation of substituted phenylacetylenes using [(Ph3P)Au(NTf2)] as the catalyst was reported by Rassadin, Kukushkin et al. [42]. Catalyst loadings of 6 mol

• addition product were obtained. We recently reported the excellent activity of the very bulky bispentiptycenyl-substituted (NHC)Au complexes in the hydration of terminal and internal alkynes [43] as well as in other transition-metal-catalyzed transformations [44][45]. We were now interested, whether

Convenient access to pyrrolidin-3-ylphosphonic acids and tetrahydro-2H-pyran-3-ylphosphonates with multiple contiguous stereocenters from nonracemic adducts of a Ni(II)-catalyzed Michael reaction

• Alexander N. Reznikov,
• Dmitry S. Nikerov,
• Anastasiya E. Sibiryakova,
• Victor B. Rybakov,
• Evgeniy V. Golovin and
• Yuri N. Klimochkin

Beilstein J. Org. Chem. 2020, 16, 2073–2079, doi:10.3762/bjoc.16.174

• metal-complexes-catalyzed [23][24][25][26] or organocatalyzed [27][28][29][30][31][32] Michael reaction is one of the most important synthetic tools for the asymmetric formation of a C–C bond. Moreover, the generation of the first stereocenter of a given configuration during the catalytic process leads

Isolation and structure determination of a tetrameric sulfonyl dilithio methandiide in solution based on crystal structure analysis and ⁶Li/¹³C NMR spectroscopic data

• Jürgen Vollhardt,
• Hans Jörg Lindner and
• Hans-Joachim Gais

Beilstein J. Org. Chem. 2020, 16, 2057–2063, doi:10.3762/bjoc.16.172

• of 2 with carbon and metal-based electrophiles revealed a high synthetic potential, allowing, for example, the synthesis of carbo- and heterocycles [4][6], and transition-metal carbene complexes [1][2], carrying the synthetically versatile sulfonyl group [7][8]. Dilithio methandiides 2 are accessible

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

• ), and the results are summarised in Table 3. The values of logKs obtained from fluorimetric and ITC experiments were generally in good agreement and minor differences within the same order of magnitude. Also, our ITC titrations revealed for all dye–polynucleotide complexes similar sets of negative

• molecules can be regarded as threading intercalators. Complexes with DNA/RNA are additionally stabilised by interactions of positively charged side chains. The spectrophotometric response of these compounds showed pronounced differences and was in some cases highly sensitive on ds-polynucleotide composition

• ][41][42]. Values for Ks and n given in Table 3 all have satisfactory correlation coefficients (>0.999). Thermal melting curves for DNA, RNA, and their complexes with the studied compounds (Table 2) were determined as previously described [39][61] by following the absorption change at 260 nm as a

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

• more stable complexes 12 with the phosphodiesters in the DNA backbone, and thus making it possible to transfect cells with shorter peptides. In 2015, the Schmuck group reported the first example of a small peptide with only four amino acids for gene transfection [27]. The binding affinity of 13 to DNA

Controlling the stereochemistry in 2-oxo-aldehyde-derived Ugi adducts through the cinchona alkaloid-promoted electrophilic fluorination

• Yuqing Wang,
• Gaigai Wang,
• Anatoly A. Peshkov,
• Ruwei Yao,
• Muhammad Hasan,
• Manzoor Zaman,
• Chao Liu,
• Stepan Kashtanov,
• Olga P. Pereshivko and
• Vsevolod A. Peshkov

Beilstein J. Org. Chem. 2020, 16, 1963–1973, doi:10.3762/bjoc.16.163

• -triggered complexation with boron trifluoride diethyl etherate. The resulting O,O-chelated boron complexes 11 turned out to be strong solid-state emitters featuring clear aggregation-induced emission (AIE) characteristics [61]. Encouraged by these results, we decided to attempt the reaction of 2-oxo

Synergy between supported ionic liquid-like phases and immobilized palladium N-heterocyclic carbene–phosphine complexes for the Negishi reaction under flow conditions

• Edgar Peris,
• Raúl Porcar,
• María Macia,
• Jesús Alcázar,
• Eduardo García-Verdugo and
• Santiago V. Luis

Beilstein J. Org. Chem. 2020, 16, 1924–1935, doi:10.3762/bjoc.16.159

• cross-coupling; NHC complex; palladium; supported ionic liquid; Introduction N-heterocyclic carbenes (NHCs) are known as efficient coordination ligands for different types of metals. The main feature of NHC complexes is their structural tunability [1]. Thus, their catalytic efficiency can be easily

• modulated through systematic variations of the steric and electronic design vectors of the NHC ligand [2]. These complexes have been used as highly efficient catalysts for a wide variety of C–C and C–X cross-coupling reactions [3]. Among others, different NHC–Pd complexes have been designed as efficient

• complexes enabling a simpler recovery and reuse of the catalysts by filtration [5]. Furthermore, the immobilized NHC-complexes can be easily adapted to flow processes using a fix-bed reactor set-up increasing simultaneously the sustainability and the efficiency of the C–C coupling reactions [6][7]. In 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

• synthesis to access up to –[CH2]10– macrocycles or acyl halides to access up to –[CH2]14– macrocycles. Seventy-five receptor–anion complexes were modelled and studied with COSMO-RS, in addition to all free host molecules. In order to predict initial selectivity towards carboxylates, 1H NMR relative

• , starting with formate. MC008 was able to fit acetate and lactate. Thus, an additional binding site was available for lactate. In the complexes of lactate with MC006–MC009, a hydrogen bond was present between the oxygen of the hydroxy group of lactate and the NH group of the macrocyclic amide. See Figure 5

• for visualization. An equilibrium likely existed between two conformers where one complex had an additional hydrogen bond and the other included intramolecularly bonded lactate. For the lactate complexes with the larger receptors, whether one dominant conformer or a mixture of two conformers was

One-pot synthesis of oxazolidinones and five-membered cyclic carbonates from epoxides and chlorosulfonyl isocyanate: theoretical evidence for an asynchronous concerted pathway

• Esra Demir,
• Ozlem Sari,
• Yasin Çetinkaya,
• Ufuk Atmaca,
• Safiye Sağ Erdem and
• Murat Çelik

Beilstein J. Org. Chem. 2020, 16, 1805–1819, doi:10.3762/bjoc.16.148

• reaction with the metal complexes or catalysts, and the reaction of a diol with toxic phosgene are the most common processes [16][17][33][34][35][36]. CSI, a highly reactive and versatile isocyanate, reacts with epoxides to give five-membered cyclic carbonates and oxazolidinones [37][38][39]. In 1984

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

• , in the 21st century there is a real renaissance for photocatalysis, with great advances achieved mainly in visible-light-mediated reactions [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]. Various photosensitizers, initially based on noble metals (such as Ir and Ru polypyridine complexes

• activation, a catalytic amount of a transition metal (generally Pd, Rh and Ru) is frequently used in combination with a stoichiometric amount of an external oxidant (typically Cu or Ag salts). Such additional oxidants are required if transiently produced low-valent metal complexes need to be reoxidized by

Clickable azide-functionalized bromoarylaldehydes – synthesis and photophysical characterization

• Dominik Göbel,
• Marius Friedrich,
• Enno Lork and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2020, 16, 1683–1692, doi:10.3762/bjoc.16.139

• inert conditions [28] are necessary to facilitate an afterglow emission. Most phosphorescence studies are focused on metal complexes due to a strong heavy atom-induced spin-orbit coupling [29][30][31][32][33]. Considering the high price and the toxicity of many metal complexes, pure organic phosphors

Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• later evaluated in the cobalt-mediated PKR [64]. The chiral enynes were treated with a stoichiometric amount of Co2(CO)8 in CH2Cl2 affording the corresponding cobalt complexes that, upon addition of an excess of NMO, underwent an efficient intramolecular PKR to afford the corresponding bicyclic

• reaction of internal alkynes with a difluorodiazoethane reagent, offering efficient access to a broad range of enantioenriched difluoromethylated cyclopropenes with almost quantitative yields and up to 97% ee [82]. This asymmetric carbene transfer reaction was performed using chiral RhII complexes, more

• described protocols for the fluorinated PKR are based on the cobalt-catalyzed version, and only a few examples have used other transition metal complexes. In this regard, significant advances can come from the careful selection of the metal complex and the CO source. The encouraging results described in

Synthesis of new dihydroberberine and tetrahydroberberine analogues and evaluation of their antiproliferative activity on NCI-H1975 cells

• Giacomo Mari,
• Lucia De Crescentini,
• Serena Benedetti,
• Francesco Palma,
• Stefania Santeusanio and
• Fabio Mantellini

Beilstein J. Org. Chem. 2020, 16, 1606–1616, doi:10.3762/bjoc.16.133

• to position 13 of the BER skeleton, usually causes a geometric propensity for additional stacking-type, noncovalent aromatic interactions with cellular targets forming stronger complexes with nucleic acids than BER [9][10][11][12]. In fact, the so obtained functionalized BER shows better anticancer