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

Acid-catalyzed rearrangements in arenes: interconversions in the quaterphenyl series

• Sarah L. Skraba-Joiner,
• Carter J. Holt and
• Richard P. Johnson

Beilstein J. Org. Chem. 2019, 15, 2655–2663, doi:10.3762/bjoc.15.258

• 1,2-phenyl shifts, while Figure 2 shows those for a 1,2-biphenyl shifts. In each case, the energy reference is arbitrarily chosen as the linear ipso cation 12c or 12d for phenyl or biphenyl shift, respectively. Predicted barriers for rearrangements of ipso cations are all in the range of 9–22 kcal/mol

• difference between ipso cations and their non-ipso counterpart which might be formed rapidly by secondary 1,2-hydride shifts. In principle, the equilibrium product in these complex reactions might correlate with relative energies of the neutral quaterphenyl isomers. Reliable heats of formation for

Formation of alkyne-bridged ferrocenophanes using ring-closing alkyne metathesis on 1,1’-diacetylenic ferrocenes

• Celine Bittner,
• Dirk Bockfeld and
• Matthias Tamm

Beilstein J. Org. Chem. 2019, 15, 2534–2543, doi:10.3762/bjoc.15.246

• . Furthermore, the ability of the new [10]ferrocenophane 2a to bind transition metal cations is outlined, and the redox properties of the new ferrocenophanes are studied by cyclovoltammetry. Results and Discussion The substrates 1a and 1b for the RCAM toward the desired ferrocenophanes 2a and 2b were

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

• the π-acidic character of pyridine rings, such as 2-oxo-6-oxypyridine, is rather weak [9][10]. Thus, pyridine[4]arenes may be expected to show a dual binding behavior towards anions and cations [8]. In addition to anion complexes also 2:1 complex formation with neutral carboxylic acids and amides have

• size are well-known for their ability to encapsulate small alkylammonium cations inside the dimer, especially quaternary ammonium cations [12][13][14]. As the cavity sizes of both pyridinearene and resorcinarene dimers are comparable, alkylammonium cations were chosen as the guests for complexation

Self-assembled coordination thioether silver(I) macrocyclic complexes for homogeneous catalysis

• Zhen Cao,
• Aline Lacoudre,
• Cybille Rossy and
• Brigitte Bibal

Beilstein J. Org. Chem. 2019, 15, 2465–2472, doi:10.3762/bjoc.15.239

• . These silver(I) complexes adopted similar structures in solution and in the solid state. As each sulfur atom in the ligand is prochiral, macrocycles L2M2 were obtained as mixtures of diastereoisomers, depending on the configurations of the sulfur atoms coordinated to silver cations. The X-ray structures

• three nitrate anions as coordinating bridges between the two symmetric M3L2 units (Figure 2). The resulting coordinated macrocycle M6L4 had a globular shape that displayed the polyaromatic ligands towards the exterior and fully encapsulated two nitrate anions and the silver(I) cations. This silver

Sugar-derived oxazolone pseudotetrapeptide as γ-turn inducer and anion-selective transporter

• Sachin S. Burade,
• Sushil V. Pawar,
• Tanmoy Saha,
• Navanath Kumbhar,
• Amol S. Kotmale,
• Manzoor Ahmad,
• Pinaki Talukdar and
• Dilip D. Dhavale

Beilstein J. Org. Chem. 2019, 15, 2419–2427, doi:10.3762/bjoc.15.234

• value of 1.26 indicated that one molecule of 2a is involved in the formation of the active transporter. The promising ion transport activity of 2a encouraged us to explore its cation and anion selectivity study by varying either cations (for MCl, M+ = Li+, Na+, K+, Rb+, and Cs+) or anions (for NaA, A

• − = F−, Cl−, Br−, I−, NO3−, SCN−, AcO− and ClO4−) of the extravesicular salt, respectively. Thus, variation of external cations, in the presence of 2a (0–10 µM), showed minor changes in the transport activity with the sequence: Na+ > Rb+ > Li+ > K+ ≈ Cs+ (Figure 7A), which suggest lesser influence of

• alkali metal cations in the transport process. However, variation of extravesicular anions demonstrated the changes in the transport behaviour with the following selectivity sequence: Cl– >> AcO– ≈ SCN– ≈ F– > NO3– >> Br– ≈ I–, showing highest selectivity for the Cl– ion (Figure 7B). Overall, anion

Synthesis of a dihalogenated pyridinyl silicon rhodamine for mitochondrial imaging by a halogen dance rearrangement

• Jessica Matthias,
• Thines Kanagasundaram,
• Klaus Kopka and
• Carsten S. Kramer

Beilstein J. Org. Chem. 2019, 15, 2333–2343, doi:10.3762/bjoc.15.226

• . Lipophilic cations such as the phosphonium cation or rhodamines are known to accumulate selectively within the mitochondria, driven by the mitochondrial plasma membrane potential [39][40]. Thereby, the high lipophilicity facilitates the diffusion through the lipid bilayers of the cell and mitochondrial

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

• intramolecular electron transfer phenomena and application in molecular devices [1][2][3][4][5]. The radical cations of bistriarylamine derivatives bis(NAr3) are well-known MV compounds having π-conjugated bridges (where NAr3 = triarylamine) [6][7][8][9][10][11][12][13][14][15][16][17][18]. These studies focused

• characteristics of the bis(NAr3)•+ radical cations are well documented due to their good availability through common N–C bond-forming reactions and the stability of the NAr3•+ unit [6][7][8][9][10][11][12][13][14][15][16][17][18]. Photoswitchable mixed valency has recently been demonstrated with bis(NAr3

• )•+ radical cations having dithienylethene bridges [21][22]. This was achieved by a regulation of the π-conjugation length through photoinduced formation/dissociation of σ bonds in the bridge, which was accomplished with changeovers from a localized system (class I) to a moderately delocalized one (class II

Synthesis of acremines A, B and F and studies on the bisacremines

• Nils Winter and
• Dirk Trauner

Beilstein J. Org. Chem. 2019, 15, 2271–2276, doi:10.3762/bjoc.15.219

• enhance the stability of the molecule, and therefore prevent decomposition, by protection of the non-participating alcohols and attempts to generate the allylic cation from a cyclic ketal [10][11][12], aiming for a Gassman-type reaction mechanism, were also unfruitful. While radical cations are known to

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

• candidates for amide bond surrogates. Interestingly, 1,2,3-triazole units can act as sensors for both anions and cations via different binding mechanisms [16][17]. The heterocyclic ring N2 and N3 atoms could realize the selective recognition of the cations whereas the C5–H···anions electrostatic interaction

• [TCNQ]−· radical anion, dragging the second [TCNQ]− near to the cavity by the help of the electrostatic stabilization supplied by the 1,2,3-triazolium cations, coupling of the two [TCNQ]−· anion radicals in the cavity and rapid formation of the sigma-connected dimer, reduction of the photogenerated

Synthesis and properties of sulfur-functionalized triarylmethylium, acridinium and triangulenium dyes

• Marco Santella,
• Eduardo Della Pia,
• Jakob Kryger Sørensen and
• Bo W. Laursen

Beilstein J. Org. Chem. 2019, 15, 2133–2141, doi:10.3762/bjoc.15.210

• functionalities were synthesized and their optical properties were studied. The sulfur functionalities were introduced by aromatic nucleophilic substitution of methoxy groups in triarylmethylium cations with ethanethiol followed by partial or full ring closure of the ortho positions with nitrogen or oxygen

• thioether donor groups. Results and Discussion Firstly, a series of triarylmethylium salts with variable number of para-methoxy substituents was synthesized. The easily achievable cations (TMP)3C+, (DMP)(TMP)2C+ and (DMP)2(TMP)C+ (Scheme 1) were prepared by their respective literature procedures [18][31

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