Multiple threading of a triple-calix[6]arene host

• Veronica Iuliano,
• Roberta Ciao,
• Emanuele Vignola,
• Carmen Talotta,
• Patrizia Iannece,
• Margherita De Rosa,
• Annunziata Soriente,
• Carmine Gaeta and
• Placido Neri

Beilstein J. Org. Chem. 2019, 15, 2092–2104, doi:10.3762/bjoc.15.207

• dialkylammonium axles [17][18][19][20][21][22][23][24][25][26] by exploiting the inducing effect of the superweak tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB) anion that gives free ‘naked’ dialkylammonium cations. In addition, we have reported interesting examples of endo-cavity complexation of

• alkylammonium cations, as TFPB− salts, inside the aromatic cavity of calixarene [20] and dihomooxacalixarene hosts [21][22]. Thus, through this ‘superweak anion’ approach, we have synthesized interesting examples of calixarene/ammonium-based interlocked structures such as calix-rotaxanes [23][24] and calix

Synthesis and anion binding properties of phthalimide-containing corona[6]arenes

• Meng-Di Gu,
• Yao Lu and
• Mei-Xiang Wang

Beilstein J. Org. Chem. 2019, 15, 1976–1983, doi:10.3762/bjoc.15.193

• cavities [22]. We have also shown that the combination of and the interplay between heteroatoms and para-(het)arylenes produce diverse macrocycles with coarse- and fine-tunable cavity shapes and sizes. The resulting coronarenes exhibit interesting molecular recognition properties towards anions, cations

• . Cations and solvent molecules are omitted for clarity. Synthesis of phthalimide-containing O6-corona[3]arene[3]tetrazines. Supporting Information Supporting Information File 372: Experimental procedures, characterization of products and copies of mass and NMR spectra. Acknowledgements We thank the

Reactions of 2-carbonyl- and 2-hydroxy(or methoxy)alkyl-substituted benzimidazoles with arenes in the superacid CF₃SO₃H. NMR and DFT studies of dicationic electrophilic species

• Dmitry S. Ryabukhin,
• Alexey N. Turdakov,
• Natalia S. Soldatova,
• Mikhail O. Kompanets,
• Alexander Yu. Ivanov,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2019, 15, 1962–1973, doi:10.3762/bjoc.15.191

• -arylmethyl-substituted benzimidazoles, in yields up to 90%. The reaction intermediates, protonated species derived from starting benzimidazoles in TfOH, were thoroughly studied by means of NMR and DFT calculations and plausible reaction mechanisms are discussed. Keywords: benzimidazoles; cations; Friedel

• their electrophilicity and electronic properties (Table 1). Apart from that, ΔG298 of the formations of cations I–IX from parent benzimidazoles 1–8 were calculated to estimate a thermodynamic possibility of the species formation (Table 1). The calculations were carried out for the solution phase in

• should be reactive electrophiles. While, in the case of hydroxyalkylbenzimidazoles 3–8, N,O-diprotonated species III, V, VII, VIII, the most probably, may be reactive intermediates. The calculation of electrophilic properties of these cations show that species I and II have higher values of

Tautomerism as primary signaling mechanism in metal sensing: the case of amide group

• Vera Deneva,
• Georgi Dobrikov,
• Aurelien Crochet,
• Daniela Nedeltcheva,
• Katharina M. Fromm and
• Liudmil Antonov

Beilstein J. Org. Chem. 2019, 15, 1898–1906, doi:10.3762/bjoc.15.185

• similar. However, as shown in Figure 5 and Table 1, the difference in the spectral maxima of the complexes allows detection of each of the studied cations. Conclusion In the current study, we modeled theoretically and experimentally the tautomerism and complexation abilities of a new tautomeric ligand

Halide metathesis in overdrive: mechanochemical synthesis of a heterometallic group 1 allyl complex

• Ross F. Koby,
• Nicholas R. Rightmire,
• Nathan D. Schley,
• Timothy P. Hanusa and
• William W. Brennessel

Beilstein J. Org. Chem. 2019, 15, 1856–1863, doi:10.3762/bjoc.15.181

• depiction of a single chain is provided in Figure 1, and a partial packing diagram is given in Figure 2. The asymmetric unit contains three alkali metal cations and three substituted allyl anions, all in general positions. Each of the three metal sites is modeled as a site disorder of atoms types K and Cs

• exhibit an average M–C(allyl) bond distance of roughly 3.17 Å). These values do not recreate distances in the homometallic complexes exactly (i.e., the average K–C distance in [KA']∞ is 3.01 Å) [17], but they reflect the relative sizes of the K+ and Cs+ cations. The structure is polymeric in two

• the only recoverable material; extracted with toluene, it crystallized from solution as the solvate. A single crystal X-ray study analysis reveals bent polymeric chains of alternating K+ cations and [A']− anions. Each potassium is capped with a toluene molecule, bonded through cation–π interactions

The cyclopropylcarbinyl route to γ-silyl carbocations

• Xavier Creary

Beilstein J. Org. Chem. 2019, 15, 1769–1780, doi:10.3762/bjoc.15.170

• substituents on the 1-position. These substrates all solvolyze in CD3CO2D to give products derived from cyclopropylcarbinyl cations that undergo further rearrangement to give 3-trimethylsilylcyclobutyl cations. These 3-trimethylsilylcyclobutyl cations are stabilized by a long-range rear lobe interaction with

• solvolysis chemistry of mesylate and triflate derivatives of trans-1-hydroxymethyl-2-trimethylsilylcyclopropane and 1-substituted analogs can be quite different since these substrates do not generally lead to 3-trimethylsilylcyclobutyl cations. Keywords: bicyclobutane; carbocation; cyclopropylcarbinyl

• contributed heavily to the development of carbocation chemistry. This article will deal with three types of carbocations that have been of intense and fundamental interest over the years, i.e., cyclopropylcarbinyl cations, electron-deficient cations, and silyl substituted carbocations. A brief overview of

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

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

• calculations [25] which were also in agreement with the earlier experiments of Bakke et al. [15]. The computational study also confirmed the hydroxide adduct Ib as the active intermediate formed in the reaction. However, Petride et al. have demonstrated that iminium cations are intermediates in the RuO4

Different reactivity of phosphorylallenes under the action of Brønsted or Lewis acids: a crucial role of involvement of the P=O group in intra- or intermolecular interactions at the formation of cationic intermediates

• Stanislav V. Lozovskiy,
• Alexander Yu. Ivanov and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2019, 15, 1491–1504, doi:10.3762/bjoc.15.151

• =)P–CR=C=CMe2, X = Cl, OMe, NR2, or SAr] undergo intramolecular cyclization into the corresponding 1,2-oxaphospholium ions in the Brønsted superacid TfOH. These cations have been thoroughly studied by means of NMR spectroscopy. The hydrolysis of superacidic solutions of these species afforded cyclic

• substituents at the phosphorus atom of phosphorylallenes [13][14][15][16]. These cations were intermediates in Brønsted and Lewis acid-promoted intramolecular reactions of phosphorus-containing allenes with aromatic π-nucleophiles giving rise to various (bi)cyclic phosphorus-containing compounds [13][14][15

• –H (Table 1). These species are formed by protonation of the central carbon atom of the allene system that gives the corresponding allyl cations, which undergo cyclization onto the oxygen of the P=O group. These ions have similar NMR data: the signal of the new proton H4 is located in the range 6.30

Cyclobutane dication, (CH₂)₄²⁺: a model for a two-electron four-center (2e-4c) Woodward–Hoffmann frozen transition state

• G. K. Surya Prakash and
• Golam Rasul

Beilstein J. Org. Chem. 2019, 15, 1475–1479, doi:10.3762/bjoc.15.148

• ° as shown in Figure 1. The structure contains conventionally two tetracoordinate and two pentacoordinate carbons. It resembles a complex between two ethylene radical cations, (CH2)42+, culminating in the formation of a 2e-4c bond. Total electron density, HOMO and LUMO of the dication 1 are depicted in

• of 1 leading to two ethylene radical cations (CH2=CH2·+) was also considered. The process was found to be exothermic by 12.8 kcal/mol at the CCSD(T)/cc-PVTZ + ZPE level. We tried, but could not locate a transition state for the dissociation process at the CCSD(T)/cc-PVTZ level. The 13C NMR chemical

Selenophene-containing heterotriacenes by a C–Se coupling/cyclization reaction

• Pierre-Olivier Schwartz,
• Sebastian Förtsch,
• Astrid Vogt,
• Elena Mena-Osteritz and
• Peter Bäuerle

Beilstein J. Org. Chem. 2019, 15, 1379–1393, doi:10.3762/bjoc.15.138

• coupling of the emerging radical cations via the more reactive α-positions forming a film on the surface of the working electrode (Scheme 3). Calculations on radical cations of heterotriacenes 1–4 clearly showed that spin density is by far highest at the α- and low at the β-positions. Therefore, we assume

• that coupling and polymerization of the radical cations occurs via the α-positions leading to mostly linear conjugated systems without branching. In subsequent scans, broad cathodic and anodic signals emerged and with increasing number of cycles the respective currents continuously increased indicating

Host–guest interactions between p-sulfonatocalix[4]arene and p-sulfonatothiacalix[4]arene and group IA, IIA and f-block metal cations: a DFT/SMD study

• Valya K. Nikolova,
• Cristina V. Kirkova,
• Silvia E. Angelova and
• Todor M. Dudev

Beilstein J. Org. Chem. 2019, 15, 1321–1330, doi:10.3762/bjoc.15.131

• between biological receptors and small ions. The complex formation behavior of water-soluble p-sulfonatocalix[4]arene and thiacalix[4]arene and group IA, IIA and f-block metal cations has been investigated computationally by means of density functional theory computations in the gas phase and in aqueous

• environment. The calculated Gibbs free energy values of the complex formation reaction of these ligands with the bare metal cations suggest a spontaneous and energy-favorable process for all metal cations in the gas phase and only for Na+, Mg2+, Lu3+ cations in water environment. For one of the studied

• cations (La3+) a supramolecular approach with explicit solvent treatment has been applied in the study of the effect of metal hydration on the complexation process. The La3+ binding to the p-sulfonatocalix[4]arene host molecule (now in the metal’s second coordination shell) is still exergonic as evidenced

Enantioselective Diels–Alder reaction of anthracene by chiral tritylium catalysis

• Qichao Zhang,
• Jian Lv and
• Sanzhong Luo

Beilstein J. Org. Chem. 2019, 15, 1304–1312, doi:10.3762/bjoc.15.129

• , the enantioselectivity was low in most cases. In addition, the synthetic efforts to access these chiral cations were generally non-trivial which limited their further development. Recently, we developed a chiral ion-pair strategy for asymmetric carbocation catalysis, with chiral trityl phosphate as

• found that less than 6% of trityl phosphate (TP) dissociated to trityl cations in the presence of a polar substrate such trifluoropyruvate [20]. In order to improve the efficiency of the dissociation, we started by first studying the properties of tritylium salts with a weakly coordinating metal-based

• Lewis acid. An estimation based on UV absorption showed that approximately 76% of TP dissociated into trityl cations in the presence of InBr3. On the other hand, tritylium salts with a weakly coordinating metal-based monophosphate or bisphosphate anion could also be obtained when trityl bromide was

Self-assembly behaviors of perylene- and naphthalene-crown macrocycle conjugates in aqueous medium

• Xin Shen,
• Bo Li,
• Tiezheng Pan,
• Jianfeng Wu,
• Yangxin Wang,
• Jie Shang,
• Yan Ge,
• Lin Jin and
• Zhenhui Qi

Beilstein J. Org. Chem. 2019, 15, 1203–1209, doi:10.3762/bjoc.15.117

• water-soluble crown macrocycle 3 was synthesized according to reported protocols, by using potassium cations as template [86][87]. The primary amine group in 3 offers diverse reaction pathways to design crown ethers appended LMW gelators, dendrimers and polymers [88][89][90][91][92]. In order to

Precious metal-free molecular machines for solar thermal energy storage

• Meglena I. Kandinska,
• Snejana M. Kitova,
• Vladimira S. Videva,
• Stanimir S. Stoyanov,
• Stanislava B. Yordanova,
• Stanislav B. Baluschev,
• Silvia E. Angelova and
• Aleksey A. Vasilev

Beilstein J. Org. Chem. 2019, 15, 1096–1106, doi:10.3762/bjoc.15.106

• identified to form complexes with alkaline-earth metal cations with higher stability constant than the respective trans isomer forms [14][15][18]. Lednev et al. proposed as an explanation of the difference in the determined stability constants values for the complexes with cis/trans isomers the formation of

• defined their photophysical behavior in neat acetonitrile (ACN) solution and in the presence of barium cations. Figure 1 shows the absorption spectra of dyes 4a–d measured at different concentrations (cM) of Ba(ClO4)2. All dye solutions have similar absorption profiles with a broad long wavelength band in

• high Ba2+ concentrations. The explanation is related to the size of the barium cation which does not intercalate completely in the crown ether cavity. This assumption is confirmed by the slight downfield shift of the signals in the 1H NMR spectrum of dye 4b in the presence of Ba2+ cations compared to

Mechanistic investigations on multiproduct β-himachalene synthase from Cryptosporangium arvum

• Jan Rinkel and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2019, 15, 1008–1019, doi:10.3762/bjoc.15.99

• , Supporting Information File 1). To shed light on the stereochemical course of the 1,3-hydride shift connecting cations D and F, a series of labelling experiments were conducted to determine the origin of the shifting hydrogen (C-1) and its destination (C-10) for 1 (Figure 8). A comparison of the 13C NMR

Mechanochemistry of supramolecules

• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2019, 15, 881–900, doi:10.3762/bjoc.15.86

• [7] followed by the lock-and-key concept of Emil Fischer in 1894 [8]. Weak or non-covalent interactions had been used systematically in the early 1960s by Lehn, Cram and Pederson to create targeted supramolecular architectures [9]. Small molecules, anions or cations could be assembled spontaneously

Coordination chemistry and photoswitching of dinuclear macrocyclic cadmium-, nickel-, and zinc complexes containing azobenzene carboxylato co-ligands

• Jennifer Klose,
• Tobias Severin,
• Peter Hahn,
• Alexander Jeremies,
• Jens Bergmann,
• Daniel Fuhrmann,
• Jan Griebel,
• Bernd Abel and
• Berthold Kersting

Beilstein J. Org. Chem. 2019, 15, 840–851, doi:10.3762/bjoc.15.81

• (7·ClO4·xEtOH; x ≈ 4): Crystals of [Ni2L(μ-azo-NMe2)]ClO4.xEtOH obtained from a mixed ethanol/acetonitrile solvent system are triclinic, space group P. The asymmetric unit comprises two crystallographically independent [Ni2L(μ-azo-NMe2)]+ cations, two ClO4– ions and 8 EtOH solvate molecules. The

• )]+ cations are structurally very similar as illustrated in Figure 8. In cation A, the co-ligand is nearly flat and coplanar with the Ni2 carboxylato plane. In cation B, the benzene rings are tilted about the azo group and the Ni2carboxlyato plane by angles of ≈32.3° and 37.5°, respectively. Interestingly, no

• blue, O red, S yellow, metals flesh (Zn, Cd) or green (Ni)). Space filling representation of the packing of two symmetry-related [Zn2L(μ-azo-NMe2)]+ cations in crystals of 5·1.5MeCN. The ClO4− anions and solvate molecules are omitted for clarity. Structure of the [Cd2L(μ-azo-NMe2)]+ cation in crystals

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

• crown ethylene bridges fall within the range of 5.4–5.5 Hz, expected for gauche stereochemistry. Such a relaxed crown conformation is suitable for accommodation of large alkali and alkaline-earth cations. The general features of FTIR-ATR spectra of receptors 3a and 3b are substantially similar to each

Syntheses and chemical properties of β-nicotinamide riboside and its analogues and derivatives

• Mikhail V. Makarov and
• Marie E. Migaud

Beilstein J. Org. Chem. 2019, 15, 401–430, doi:10.3762/bjoc.15.36

• hexachloroacetone [28][71] or cobalt(II) acetate in the presence of hydrogen peroxide followed by removal of the cobalt cations with QuadraSil AP resin [60]. The nature of the counter anion vary as a function of the conditions applied. Reduction of N1-substituted 3-nicotinamide salts to the corresponding 1,4

Study on the regioselectivity of the N-ethylation reaction of N-benzyl-4-oxo-1,4-dihydroquinoline-3-carboxamide

• Pedro N. Batalha,
• Luana da S. M. Forezi,
• Maria Clara R. Freitas,
• Nathalia M. de C. Tolentino,
• Ednilsom Orestes,
• José Walkimar de M. Carneiro,
• Fernanda da C. S. Boechat and
• Maria Cecília B. V. de Souza

Beilstein J. Org. Chem. 2019, 15, 388–400, doi:10.3762/bjoc.15.35

• carboxamide group, may contribute to enhance the bioactivity. This fact could be explained by the coplanarity induced by the C-4 carbonyl hydrogen bond interactions with biological targets [3] or complexation with physiological metal cations such as magnesium and zinc [23]. Besides the derivatives 3a and 3b

N-Arylphenothiazines as strong donors for photoredox catalysis – pushing the frontiers of nucleophilic addition of alcohols to alkenes

• Fabienne Speck,
• David Rombach and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2019, 15, 52–59, doi:10.3762/bjoc.15.5

• fast access to a wide variety of catalysts. Recently it was shown that the radical cation of the photoredox catalyst can play a key role in photoinduced oxidation chemistry [16]. This is rather unusual due to the usually short lifetime of radical cations in solution attributed to their low-lying

Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region

• Aude-Héloise Bonardi,
• Frédéric Dumur,
• Guillaume Noirbent,
• Jacques Lalevée and
• Didier Gigmes

Beilstein J. Org. Chem. 2018, 14, 3025–3046, doi:10.3762/bjoc.14.282

• catalytic cycles used in organic chemistry, the development of photoredox catalysis for photopolymerization reactions has been proposed. It has emerged as a significant innovation in the field of photoinitiated polymerization. Photoredox catalysis is a new strategy to generate radicals and/or cations upon

• named reduction agent, RA2 in Figure 1) by a redox reaction. In a reductive cycle, the PC* reacts first with a reduction agent (in Figure 1, RA1) which leads to PC●− and RA1●+. Then, PC can be regenerated with an oxidation agent (OA2). Radicals and cations are generated in these cycles [16]. As we can

• the case of a d5 high spin octahedral complex in Figure 4. As for LMCT, MLCT give intense band in UV spectrum. 1.4 Mechanisms in polymerization reactions Free radical polymerization or/and cationic polymerization can be initiated by photoredox catalysis. Respectively, radicals or/and cations must be

Nucleofugal behavior of a β-shielded α-cyanovinyl carbanion

• Rudolf Knorr and
• Barbara Schmidt

Beilstein J. Org. Chem. 2018, 14, 3018–3024, doi:10.3762/bjoc.14.281

• . Alternatively, carbonyl additions to 2Li might be generally retarded (relative to protonations) on account of the clustered [4] ground state structure of 2Li in solution. Electrophilic cations (Li+ or K+) are not necessary (albeit perhaps helpful) for the addition of the carbanion unit of 2Li or 2K to carbonyl

1,8-Bis(dimethylamino)naphthyl-2-ketimines: Inside vs outside protonation

• A. S. Antonov,
• A. F. Pozharskii,
• P. M. Tolstoy,
• A. Filarowski and
• O. V. Khoroshilova

Beilstein J. Org. Chem. 2018, 14, 2940–2948, doi:10.3762/bjoc.14.273

• , leading to the formation of stabilised cations. In our recent work, we observed for the first time that the ortho-ketimino group in 4a can compete with the proton sponge moiety for the proton, which results in the formation of equilibria between the forms 4b (protonated to the proton sponge fragment) and

• Synthesis of DMAN-ortho-ketimines and their cations Target compounds 4a–7a were synthesised by techniques previously developed in our laboratory (Scheme 4) [7][8]. Compounds 4a–6a were obtained by the treatment of the ortho-lithium derivative 8 with the corresponding nitrile (path a). Unfortunately, the