A new approach to silicon rhodamines by Suzuki–Miyaura coupling – scope and limitations

• Thines Kanagasundaram,
• Antje Timmermann,
• Carsten S. Kramer and
• Klaus Kopka

Beilstein J. Org. Chem. 2019, 15, 2569–2576, doi:10.3762/bjoc.15.250

• optimizations of the reaction conditions could lead to the silicon rhodamine 22 in moderate yields, an inseparable impurity of the cationic fluorophore was detected. After identifying this impurity as the tetraphenylphosphonium cation, we exchanged the triphenylphosphine ligand of the catalyst with dppf (1,1

α,ß-Didehydrosuberoylanilide hydroxamic acid (DDSAHA) as precursor and possible analogue of the anticancer drug SAHA

• Shital K. Chattopadhyay,
• Subhankar Ghosh,
• Sarita Sarkar and
• Kakali Bhadra

Beilstein J. Org. Chem. 2019, 15, 2524–2533, doi:10.3762/bjoc.15.245

• with DAPI staining revealed a significant increase in nucleosomal fragmentation and nuclear condensation in 11b treated cells with increasing doses (Figure 6 upper panel) [39]. Furthermore, a cellular functional assay by JC-1 probe, a voltage sensitive fluorescent cationic dye, exhibits membrane

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

• to the electron-poor nature of the pyridine ring. Herein, we demonstrate the encapsulation of Me4N+ cations inside a dimeric hydrogen-bonded pyridine[4]arene capsule, which contradicts with earlier assumptions. The complexation of a cationic guest inside the pyridine[4]arene dimer has been detected

• dimeric and hexameric capsules, which can encapsulate cationic and neutral guests [1][2][3]. Pyridine[4]arenes [4] are analogous macrocycles to resorcin[4]arenes. Whereas resorcinarenes are cyclic tetramers of resorcinol, pyridinearenes are formed from 2,6-dihydroxypyridine (see Scheme 1). Although the

• positive potential on the surface of the cavity, except on the N–H hydrogen atoms. They are, however, on tangential positions along the capsules surface, and therefore do not significantly contribute to anion binding [8]. More recently, we were also able to demonstrate that cationic transition metal

Current understanding and biotechnological application of the bacterial diterpene synthase CotB2

• Ronja Driller,
• Daniel Garbe,
• Norbert Mehlmer,
• Monika Fuchs,
• Keren Raz,
• Dan Thomas Major,
• Thomas Brück and
• Bernhard Loll

Beilstein J. Org. Chem. 2019, 15, 2355–2368, doi:10.3762/bjoc.15.228

• Figure 7). F107 has been targeted by site-directed mutagenesis as well (Table 2 and Scheme 1) [30], leading to compounds R-cembrene A (7) and cyclooctat-1,7-diene (8). Now the cationic intermediate has two possibilities to react to G, either by a 1,3- and 1,5-hydride shift or by two 1,2-hydride shifts

Isolation and biosynthesis of an unsaturated fatty acid with unusual methylation pattern from a coral-associated bacterium Microbulbifer sp.

• Amit Raj Sharma,
• Enjuro Harunari,
• Tao Zhou,
• Agus Trianto and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2019, 15, 2327–2332, doi:10.3762/bjoc.15.225

• only single example of C-methylation with SAM at a carbon derived from the carbonyl carbon of acetate (C1; Figure 3D) is reported for sphingolipid biosynthesis in the yeast, Pichia pastoris [16]. SAM-dependent C-methylation takes place at the alkenyl carbon C9 of glucosylceramide, yielding a cationic

• and methylation takes place at C3 to give a putative cationic intermediate. The following proton loss from C3 is probable to give directly 1 in a similar fashion to the glucosylceramide biosynthesis. Branched chain fatty acids are commonly present in cell membranes, and mono-methylation at the iso or

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

• higher, respectively, than the redox potential for Ph1b, affording a large split in the redox potentials of 144 mV. These results clearly indicate the consecutive oxidation of the NAr3 units in 1b and the formation of the cationic and dicationic species, 1b+ and 1b2+ (Equation 1). It is notable that the

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• process, an in situ-generated cationic [Pd(NO3)]+ species facilitates the C–H bond activation to give intermediate A. The Pd(II)(1a)2 complex B is formed via further C–H bond activation of another molecule 1a by the cyclopalladation(II) intermediate A. Then, intermediate B undergoes oxidative addition by

• reagents, such as cationic, anionic and radical CF3 sources have been discovered and offer manifold choices to effect electrophilic, nucleophilic and radical trifluoromethylation [103] (Figure 1). The selection of the trifluoromethylation reagent has become the main factor in the optimization of these

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• by inserting a photoactive binding motif into a cyclophane [58]. In this regard, Li et al. have synthesized a cationic cyclophane 13 (Figure 11) based on an electron poor naphthalenediimide (NDI) moiety and cationic 1,2,3-triazolium units. Cyclophane 13 was employed to control the interactions

An overview of the cycloaddition chemistry of fulvenes and emerging applications

• Ellen Swan,
• Kirsten Platts and
• Anton Blencowe

Beilstein J. Org. Chem. 2019, 15, 2113–2132, doi:10.3762/bjoc.15.209

• ][63][64][65][66][67]. By considering the dipolar resonance structures of fulvenes, whereby either cationic (1a and 2a) or anionic (1b and 2b) charged centres are formed at the cyclic carbon of the exocyclic double bond, their aromatic character and reactivity becomes more predictable [1][2][5][9][30

A review of the total syntheses of triptolide

• Xiang Zhang,
• Zaozao Xiao and
• Hongtao Xu

Beilstein J. Org. Chem. 2019, 15, 1984–1995, doi:10.3762/bjoc.15.194

• cationic polyene cyclization, transition-metal- or photocatalyst-mediated radical polyene cyclization [72]. The key to such transformation is to install a proper initiator within the substrate such as an allylic alcohol, an acetal, an aziridine, an N-acetal, a hydroxylactam, or a 1,3-dicarbonyl moiety. van

• Tamelen and co-workers originally reported a nature-inspired acid-induced cationic polyene cyclization to construct the key trans-decalin scaffold (A- and B-ring) of triptolide (Figure 2, Scheme 6 and route H) [73]. In their synthesis, 2-isopropylphenol (31) was used as starting material to construct the

• and its relatives from commercially available acid 32 (Figure 2, route J and Scheme 8) [46]. This synthesis highlights the utilization of an indium(III)-catalyzed cationic polycyclization of 17 and a palladium-catalyzed carbonylation–in situ lactone formation to construct the key intermediate 94

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

• superacids or coordination by a Lewis superacid to produce a di- (tri- or higher) cationic species, the study of superelectrophilic activation became a very active area of research [11][12][13]. The acid-catalyzed condensation of ketones and aldehydes with aromatic compounds is known as the hydroxyalkylation

• superelectrophilic activation approach, we have developed a useful synthetically procedure for the modification of the benzimidazole structure. Examples of some commercially available pharmaceuticals and agrochemicals containing the benzimidazole scaffold. Formation of cationic species by protonation of 5-formyl-4

Analysis of sesquiterpene hydrocarbons in grape berry exocarp (Vitis vinifera L.) using in vivo-labeling and comprehensive two-dimensional gas chromatography–mass spectrometry (GC×GC–MS)

• Philipp P. Könen and
• Matthias Wüst

Beilstein J. Org. Chem. 2019, 15, 1945–1961, doi:10.3762/bjoc.15.190

• photoinduced [2 + 2]-cycloaddition is very unlikely. The biosynthesis of β-bourbonene can be performed by cationic cyclization, as shown in Scheme 4. A total of 5 bicyclic, aromatic sesquiterpene hydrocarbons (21–25) with a cadinane skeleton were found in exocarp of the grape variety Lemberger, whose identity

Identification of optimal fluorescent probes for G-quadruplex nucleic acids through systematic exploration of mono- and distyryl dye libraries

• Xiao Xie,
• Michela Zuffo,
• Marie-Paule Teulade-Fichou and
• Anton Granzhan

Beilstein J. Org. Chem. 2019, 15, 1872–1889, doi:10.3762/bjoc.15.183

• cationic dyes was synthesized and investigated with respect to their optical properties, propensity to aggregation in aqueous medium, and capacity to serve as fluorescence “light-up” probes for G-quadruplex (G4) DNA and RNA structures. Among the 61 compounds, 57 dyes showed preferential enhancement of

• . Along these lines, we have previously reported that cationic styryl-type dyes, such as distyrylpyridinium derivatives 1a and 2a (Figure 1) represent a promising starting point for the development of fluorescent probes selective for a variety of G4-DNA structures [58]. Another distyryl dye, namely

• electron-donating lateral aromatic groups Ar (a–Þ), the cationic heterocyclic core Het+ (1–16) and, in the case of 2,4-disubstituted derivatives (1–6), the substituent R (Figure 2). Among these, several distyryl dyes (1o, 1x, 7x [64] and 10a [65]) have been previously reported as fluorescent probes for

The cyclopropylcarbinyl route to γ-silyl carbocations

• Xavier Creary

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

• the γ-trimethylsilyl group. When the substituent is electron-withdrawing (CF3, CN, or CO2CH3), significant amounts of bicyclobutane products are formed. The bicyclobutanes are a result of γ-trimethylsilyl elimination from the cationic intermediate that has an unusually long calculated Si–C bond. The

• [12] leaving groups, reacted in aqueous solvents to give an identical mixture of products 3, 4, and 5 (Scheme 1). Additionally, solvolysis rates were far greater than expected for primary and strained secondary systems. To account for these facts, it has been suggested that there are common cationic

• cation (a cation containing hypercoordinated carbon) that could be derived from protonation of bicyclobutane [20]. Another potential mode of stabilization is by an interaction of the cationic center with the adjacent strained cyclobutyl bonds as in 7b. A second class of carbocations that this article

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

• in an aqueous medium (Scheme 9). In order to increase the solubility of reactants in aqueous medium cationic surfactant (cetyl trimethylammonium bromide: CTAB) has been used which has also increased the yield of the product. Aliphatic aldehydes resulted in lower yields (65 and 76%) whereas

Molecular basis for the plasticity of aromatic prenyltransferases in hapalindole biosynthesis

• Takayoshi Awakawa and
• Ikuro Abe

Beilstein J. Org. Chem. 2019, 15, 1545–1551, doi:10.3762/bjoc.15.157

• , and the other PTases, but W119 is conserved or substituted with tyrosine among all of the aligned PTases (Figure 6). The aromatic amino acids around W119 are also important to support the aromatic substrates and cationic intermediates in the X-ray structural studies of CloQ and EpzP [28][30]. The

Superelectrophilic carbocations: preparation and reactions of a substrate with six ionizable groups

• Sean H. Kennedy,
• Makafui Gasonoo and
• Douglas A. Klumpp

Beilstein J. Org. Chem. 2019, 15, 1515–1520, doi:10.3762/bjoc.15.153

• proposed involving tetra-, penta-, or hexacationic species. Keywords: cation; Friedel–Crafts; heterocycle; superacid; superelectrophile; Introduction During the 1970s and 80s, Olah and co-workers described the novel chemistry of highly-charged organic cationic species. This work lead to the concept of

• sufficiently acidic media, cationic electrophiles such as the nitronium ion may undergo protonation, leading to the nitronium dication (1), and a greatly enhanced electrophilic reactivity. In superacidic solutions, nitronium salts have been shown to react with deactivated arenes and saturated hydrocarbons

• (including methane) [6][7][8][9]. Numerous studies from our group and others have shown that relatively stable cationic centers – such as ammonium, phosphonium, and pyridinium groups – may also be part of superelectrophilic systems [10]. Recently, we described the chemistry of tri-, tetra-, and pentacationic

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

• intermolecular hydroarylation of allenes bearing electron-withdrawing substituents. Plausible reaction mechanisms have been proposed on the basis of the investigated reactions, and NMR analysis and DFT studies of the intermediate cationic species. Keywords: aluminum chloride; cation; intermediate

• electrophilic activation with Brønsted or Lewis (super)acids, including reactions with arenes as π-nucleophiles, and investigation of intermediate cationic species by means of NMR and DFT calculations. Allenes used in this study are presented in Figure 1. We explored allenes having different substituents at the

• these reactions in excellent yields. The plausible reaction mechanism includes at the first stage nucleophilic attack of morpholine onto the phosphorus cationic center that gives cation I, which is transformed into species J. Hydrolysis of the latter leads to cation K and then finally to amides 6a,b. We

Borylation and rearrangement of alkynyloxiranes: a stereospecific route to substituted α-enynes

• Ruben Pomar Fuentespina,
• José Angel Garcia de la Cruz,
• Gabriel Durin,
• Victor Mamane,
• Jean-Marc Weibel and
• Patrick Pale

Beilstein J. Org. Chem. 2019, 15, 1416–1424, doi:10.3762/bjoc.15.141

• ] transferring the non-oxygenated boron substituent and promoting oxirane ring opening [39]. The group’s migratory aptitude cannot be directly compared to that known from cationic rearrangements, because the nature of the other boron substituents plays a key role in migration, as revealed by calculations [40][41

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

• of water-soluble calixarenes and cationic guests are important in understanding the possible cooperative/competitive contributions of different intramolecular interactions working between the host and guest species. Knowledge (at molecular level) of structural/functional information, energetics

• + Mn+ → [C[4]A–M](4−n)− and TC[4]A + Mn+ → [TC[4]A–M](4−n)−. Metal cationic radii (Å). Supporting Information Supporting Information File 144: Validation of the chosen computational level, additional structural data and thermodynamic parameters for the complex formation reactions.

Bambusuril analogs based on alternating glycoluril and xylylene units

• Tomáš Lízal and
• Vladimír Šindelář

Beilstein J. Org. Chem. 2019, 15, 1268–1274, doi:10.3762/bjoc.15.124

• which can interact with cationic, anionic or neutral guest molecules. Here we present the design and synthesis of a new hybrid macrocycle containing glycoluril and aromatic units. The reaction afforded a mixture of macrocyclic homologues from which a two-membered macrocycle was isolated as the main

Steroid diversification by multicomponent reactions

• Leslie Reguera,
• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Daniel G. Rivera

Beilstein J. Org. Chem. 2019, 15, 1236–1256, doi:10.3762/bjoc.15.121

• the natural cationic peptide antibiotics [60] or as a way to constrain peptide sequences in protein epitope conformations [61]. In this regard, the groups of Rivera and Wessjohann have pioneered the utilization of MCRs for the conjugation of oligosaccharides [62] and peptides [63][64] to steroids

Phylogenomic analyses and distribution of terpene synthases among Streptomyces

• Lara Martín-Sánchez,
• Kumar Saurabh Singh,
• Mariana Avalos,
• Gilles P. van Wezel,
• Jeroen S. Dickschat and
• Paolina Garbeva

Beilstein J. Org. Chem. 2019, 15, 1181–1193, doi:10.3762/bjoc.15.115

• substrate 2-methyl-GPP to form 2-MIB (2) [25][26]. An S-adenosylmethionine (SAM) dependent methyl transferase is responsible for the methylation of GPP into 2-methyl-GPP (14, Scheme 2). Its isomerisation to 15 allows for a cyclisation via the cationic intermediates B and C to 2. Genes encoding for SAM

• -MIB (2). First, GPP is methylated to 14 by a SAM-dependent methyltransferase, followed by a terpene synthase catalysed cyclisation through a cationic cascade to 2. Oxidation products derived from 3 by the cytochrome P450 monooxygenase that is genetically clustered with the epi-isozizaene synthase in

Design of a double-decker coordination cage revisited to make new cages and exemplify ligand isomerism

• Sagarika Samantray,
• Sreenivasulu Bandi and
• Dillip K. Chand

Beilstein J. Org. Chem. 2019, 15, 1129–1140, doi:10.3762/bjoc.15.109

• 658.14 and 285.57, respectively, which correspond to the cationic fragments [1b − BF4]+ and [1b − 2BF4]2+ that are formed due to the loss of one and two units of counter anions from 1b. The experimental and theoretical peak patterns were found to be in agreement. The data of 1c and 1d are given in

• mononuclear complexes. The ESIMS spectrum of compound 3a (Supporting Information File 1, Figure S33) showed isotopic peak patterns at m/z 866.10 and 402.05, respectively, which corresponds to the cationic fragments [3a − NO3]+ and [3a − 2NO3]2+ that are formed due to the loss of one and two units of counter

• , Figure S42). Isotopic peak patterns are found at m/z 982.04, 634.03 and 460.03, which correspond to the cationic fragments [4a − 2NO3]2+, [4a − 3NO3]3+ and [4a − 4NO3]4+ that are formed due to the loss of two, three and four units of counter anions from 4a. The experimental and theoretical peak patterns

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

• -enhancement effect that is analogous to the squaraine guest back-folding described above. In this present case, the anionic Z groups that are peripherally appended to a tetralactam host are long enough to fold back and provide stabilizing secondary interactions with a cationic glucosammonium guest inside the