CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• ). This dication reacts with benzene to provide pyridinium–oxonium dication 159 in solution. Further arylation does not occur spontaneously, which was evident because alcohol 157 was isolated at the end of the reaction. Upon heating at 60 °C, the second arylation takes place, presumably via the formation

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• ]arene. Pillararenes have electron-rich cavities that facilitate the combination with various electron-deficient guest molecules, such as alkylammonium, pyridinium, and imidazolium cations. Compared to other macrocycles, pillararenes exhibit a high degree of symmetry and rigidity, which gives them a

Recent progress in the synthesis of homotropane alkaloids adaline, euphococcinine and N-methyleuphococcinine

• Dimas J. P. Lima,
• Antonio E. G. Santana,
• Michael A. Birkett and
• Ricardo S. Porto

Beilstein J. Org. Chem. 2021, 17, 28–41, doi:10.3762/bjoc.17.4

• (±)-15 and (±)-16, which were oxidized with pyridinium chlorochromate giving the alkaloids (±)-adaline (1) and (±)-euphococcinine (2), respectively. The synthetic route performed by the authors allowed accessing both racemic homotropane alkaloids in 8 steps, starting from alcohol 5 (or 6) in 15.0–25.3

Synthesis and investigation of quadruplex-DNA-binding, 9-O-substituted berberine derivatives

• Jonas Becher,
• Daria V. Berdnikova,
• Heiko Ihmels and
• Christopher Stremmel

Beilstein J. Org. Chem. 2020, 16, 2795–2806, doi:10.3762/bjoc.16.230

• and high selectivity towards telomeric G-quadruplex DNA [34][35][36][37]. Representative examples of this class of compounds are the 9-O-aminoalkyl-substituted and 9-O-pyridinium-N-alkyl-substituted derivatives 1bn and 1cn or the 13-phenylalkyl-substituted substrates 1dn or 1en (Scheme 1) [38][39][40

• delicate balance between the hydrophobic effects of the alkyl chain and the thermodynamically favorable interactions on the association of ammonium or pyridinium groups in the grooves and loops was assessed. In another approach with a cyanine-based ligand, the alkyl substituents with a suitable length were

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

• % overall yield. Ammonium and pyridinium guests were synthesized in 4–5 steps. The TLC knot-forming sequence was carried out and produced a product with the expected molecular weight, but, unfortunately, further characterization did not produce conclusive results regarding the topology of the product

• (ammonium) 2 and bis(pyridinium) 3 (Figure 1). The electron-rich macrocycles of host 1 might also render it useful for other molecular recognition applications. A principle goal driving our second-generation TLC approach was to test the lower limit on the size of a molecular trefoil knot. In 2008 we

• expected, the methylene groups closest to the nitrogen atom shifted the most (>0.8 ppm for each). The IR spectrum also supports the structure of 2, as strong peaks for both an azide asymmetric stretch (ν 2099 cm−1) and a PF6− stretching vibration (ν 845 cm−1) were observed. The synthesis of bis(pyridinium

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

• on subsequent Tamao–Fleming oxidation provided the exo-diol 18 in an overall good yield with 99% enantiomeric excess (Scheme 3). Furthermore, the diol 18 was converted into the corresponding diketone 19 using pyridinium chlorochromate (PCC) as an oxidizing agent. Interestingly, they have also

• displayed in Scheme 17. Amaya et al. in 2009 have revealed the synthesis of monobromosumanene 82 from sumanene (2) by treating it with pyridinium perbromide as displayed in Scheme 18 [49]. In this report, the authors have exposed the anisotropic electron transport properties of the needle-like single

Nonenzymatic synthesis of anomerically pure, mannosyl-based molecular probes for scramblase identification studies

• Giovanni Picca,
• Markus Probst,
• Simon M. Langenegger,
• Oleg Khorev,
• Peter Bütikofer,
• Anant K. Menon and
• Robert Häner

Beilstein J. Org. Chem. 2020, 16, 1732–1739, doi:10.3762/bjoc.16.145

• dissolved in anhydrous ethanol (8 mL), and pyridinium p-toluenesulfonate (PPTS, 286 mg, 1.14 mmol, 2 equiv) was added. The solution was stirred at 60 °C for 2.5 h. The reaction mixture (at rt) was poured into a separating funnel containing diethyl ether (40 mL) and brine (16 mL). The organic layer was dried

Synthesis of 3-substituted isoxazolidin-4-ols using hydroboration–oxidation reactions of 4,5-unsubstituted 2,3-dihydroisoxazoles

• Lívia Dikošová,
• Júlia Laceková,
• Ondrej Záborský and
• Róbert Fischer

Beilstein J. Org. Chem. 2020, 16, 1313–1319, doi:10.3762/bjoc.16.112

• (Scheme 3). Dess–Martin periodinane was chosen as the oxidizing agent [33][34] as our primary choice, pyridinium dichromate, prove to be insufficiently effective even at an elevated temperature. The reaction in anhydrous dichloromethane at 0 °C led to the desired isoxazolidin-4-ones 9a–c in moderate

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

• corresponding pyridinium and the desired carbamoyl radical. The latter can be intercepted by an organonickel species resulting from the oxidative addition of the nickel catalyst to the aryl bromides 19.2. The arylamides 19.3 are obtained following a reductive elimination, and the resulting Ni(I) species is

• photocatalyst, which triggers the photoinduced SET reduction of the N-alkoxypyridinium salt 39.1, leading to the formation of the key O-radical. This species rapidly undergoes a 1,5-HAT. The formed nucleophilic C-centered radical then adds selectively onto the C4 position of another pyridinium substrate 39.1

Fluorinated phenylalanines: synthesis and pharmaceutical applications

• Laila F. Awad and
• Mohammed Salah Ayoup

Beilstein J. Org. Chem. 2020, 16, 1022–1050, doi:10.3762/bjoc.16.91

• affecting the newly introduced fluorine atom was attempted by a two-step, one-pot protocol involving an in situ esterification of a highly electrophilic pyridinium triflate intermediate [77] and afforded the anti-β-fluoro-α-amino acid methyl ester 160a in 52% yield and with 98.8% ee (Scheme 39). On the

Copper-catalysed alkylation of heterocyclic acceptors with organometallic reagents

• Yafei Guo and
• Syuzanna R. Harutyunyan

Beilstein J. Org. Chem. 2020, 16, 1006–1021, doi:10.3762/bjoc.16.90

• research. In an attempt to overcome this reactivity issue, the same authors decided to use the trimethylsilyl-based Lewis acid TMSOTf in order to allow the covalent activation of the alkenylpyridine via pyridinium formation. This strategy turned out successful, and optimisation studies identified reaction

Photocatalytic deaminative benzylation and alkylation of tetrahydroisoquinolines with N-alkylpyrydinium salts

• David Schönbauer,
• Carlo Sambiagio,
• Timothy Noël and
• Michael Schnürch

Beilstein J. Org. Chem. 2020, 16, 809–817, doi:10.3762/bjoc.16.74

• Dolech 2, 5612 AZ Eindhoven, The Netherlands 10.3762/bjoc.16.74 Abstract A ruthenium-catalyzed photoredox coupling of substituted N-aryltetrahydroisoquinolines (THIQs) and different bench-stable pyridinium salts was successfully developed to give fast access to 1-benzyl-THIQs. Furthermore, secondary

• interest [27]. In our continuing quest to develop methods for the introduction of pure hydrocarbon residues avoiding volatile reagents [28][29], our attention was drawn to stable N-alkyl-(2,4,6-triphenyl)pyridinium salts (Katritzky salts) as alkylation reagents in the context of non-directed C–H

• functionalization. These salts are known since the late 1970s [30], but only in the last few years they have found application in a wide variety of radical processes, initiated by a single-electron reduction of the pyridinium salts, and subsequent generation of alkyl radicals [31][32][33][34]. Among these

Aerobic synthesis of N-sulfonylamidines mediated by N-heterocyclic carbene copper(I) catalysts

• Faïma Lazreg,
• Marie Vasseur,
• Alexandra M. Z. Slawin and
• Catherine S. J. Cazin

Beilstein J. Org. Chem. 2020, 16, 482–491, doi:10.3762/bjoc.16.43

• obtained by the reaction of the isolated hydroxide derivative [Cu(IPr)(OH)] [29] with pyridinium trifluoromethanesulfonate, while the biscarbene complexes 5 and 6 were obtained from the corresponding [Cu(NHC)Cl] through the in situ formation of the corresponding hydroxide complex [Cu(NHC)(OH)] [20] which

• )copper(I) triflate, [Cu(IPr)(Pyr)]OTf (4). In a glovebox, a vial was charged with [Cu(OH)(IPr)] (200 mg, 0.41 mmol), pyridinium trifluoromethanesulfonate (94.0 mg, 1 equiv, 0.41 mmol) and THF (2 mL). The reaction mixture was stirred at room temperature for 15 hours. The solution was concentrated and

Architecture and synthesis of P,N-heterocyclic phosphine ligands

• Wisdom A. Munzeiwa,
• Bernard Omondi and
• Vincent O. Nyamori

Beilstein J. Org. Chem. 2020, 16, 362–383, doi:10.3762/bjoc.16.35

• relatively good yields. Notably, a low isolated yield was reported when starting from 2-(4-chlorobutyl)pyridine (n = 4) and this was attributed to the competing cyclization reaction affording cyclic pyridinium salts. The prominent 2-(diphenylphosphine)pyridine (4) has proved to be an interesting building

• treated with triflic anhydride to afford the corresponding triflate 55. Microwave-assisted reduction of compound 55 with pyridinium chloride afforded the α-chloropyridine derivative 56, which was further catalytically dehalogenated with palladium on carbon and formic acid to generate the pyridine scaffold

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

• effective molarity and the favorable orientation of the substrates inside the cavity [61]. Thus, a nanometer-sized macrocyclic receptor based on a photoactive porphyrin unit and anion-binding pyridinium and 1,2,3-triazolium units 15 was reported by Li and co-workers This receptor was synthesized via well

Bipolenins K–N: New sesquiterpenoids from the fungal plant pathogen Bipolaris sorokiniana

• Chin-Soon Phan,
• Hang Li,
• Simon Kessler,
• Peter S. Solomon,
• Andrew M. Piggott and
• Yit-Heng Chooi

Beilstein J. Org. Chem. 2019, 15, 2020–2028, doi:10.3762/bjoc.15.198

• previously reported sativene-type sesquiterpenoids 5 (isolated from B. eleusines and Cochliobolus sp., and from semi-synthetic analogue of prehelminthosporol with pyridinium chlorochromate or chromic acid) [1][4][18][26], 8 (isolated from B. eleusines) [3][6], and 10 (isolated from Bipolaris sp. and

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

• pyridinium fragments have been described as bright, photostable stains for double-stranded DNA, although their interaction with G4 structures has not been assessed [68][69][70]. All dyes, except for distyryl derivative 6a and mono-styryl derivative 19a, were obtained through a piperidine-catalyzed

• : replacement of the 2,4-pyridinium unit in dye 1a with a 2,6-pyridinium (7a) or a 2,4-quinolizinium moiety (11a) leads to a blue shift of the absorption maximum, whereas all other heterocyclic units lead to significantly stronger (10a, 14a) and/or red-shifted (9a, 12a, 13a) absorption bands (Table 1 and Figure

•  4B). On the other hand, the nature of the substituent R in the 2,4-pyridinium unit has only a minor influence on the optical properties, and the absorption bands of the dyes 2a–6a are only slightly red-shifted (by 10–20 nm in MeOH) with respect to that of 1a. Fluorimetric response of dyes towards DNA

A metal-free approach for the synthesis of amides/esters with pyridinium salts of phenacyl bromides via oxidative C–C bond cleavage

• Kesari Lakshmi Manasa,
• Yellaiah Tangella,
• Namballa Hari Krishna and
• Mallika Alvala

Beilstein J. Org. Chem. 2019, 15, 1864–1871, doi:10.3762/bjoc.15.182

• 10.3762/bjoc.15.182 Abstract An efficient, simple, and metal-free synthetic approach for the N- and O-benzoylation of various amines/benzyl alcohols with pyridinium salts of phenacyl bromides is demonstrated to generate the corresponding amides and esters. This protocol facilitates the oxidative cleavage

• of a C–C bond followed by formation of a new C–N/C–O bond in the presence of K2CO3. Various pyridinium salts of phenacyl bromides can be readily transformed into a variety of amides and esters which is an alternative method for the conventional amidation and esterification in organic synthesis. High

• functional group tolerance, broad substrate scope and operational simplicity are the prominent advantages of the current protocol. Keywords: amidation; benzoylation; benzylamines; pyridinium salt of phenacyl bromides; Introduction Amidation and esterification are fundamental transformations in synthetic

Application of chiral 2-isoxazoline for the synthesis of syn-1,3-diol analogs

• Juanjuan Feng,
• Tianyu Li,
• Jiaxin Zhang and
• Peng Jiao

Beilstein J. Org. Chem. 2019, 15, 1840–1847, doi:10.3762/bjoc.15.179

• oxidation of the free hydroxy to the carboxy group via intermediary aldehyde was then examined. Swern or pyridinium chlorochromate (PCC) oxidation of 4 also gave a complicated mixture without the desired aldehyde detected. These failed reactions indicated that the 2-isoxazoline moiety could not survive

Complexation of 2,6-helic[6]arene and its derivatives with 1,1′-dimethyl-4,4′-bipyridinium salts and protonated 4,4'-bipyridinium salts: an acid–base controllable complexation

• Jing Li,
• Qiang Shi,
• Ying Han and
• Chuan-Feng Chen

Beilstein J. Org. Chem. 2019, 15, 1795–1804, doi:10.3762/bjoc.15.173

• complex H1·G1 was obtained by vapor diffusion of isopropyl ether into acetone. As shown in Figure 4, G1 was encapsulated in the cavity of H1 to form a 1:1 complex, in which G1 is distorted by the dihedral angle between the pyridinium rings of 33.19°. There exist multiple CH···π interactions between the

• protons of G1 and the aromatic rings of H1 with distances of 2.683 for A, 2.845 for B, 2.788 for C, 2.802 for D, and 2.868 Å for E, respectively. There also exist π–π stacking interactions between the pyridinium of G1 and the aromatic ring of H1 with the distance of 3.854 Å for F, a CH···O hydrogen bond

• Information File 1, Figure S92). The calculation results revealed the C–H···π interactions between the protons on the pyridinium ring of G1 and the benzene ring units of the host H4 and C–H···O hydrogen bonds between the protons of the methyl group and pyridinium rings of G1 and the oxygen atom of H4 with

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

• more. It was observed that most of the methods utilize 2-aminopyridines as one of the starting materials due to its binucleophilic nature; associated with exocyclic amino group and endocyclic pyridinium nitrogen [19]. Recently, A3 coupling of alkynes, aldehydes, and aminopyridines have been developed

• performed a Cu(OAc)2-Et3N-mediated coupling reaction of α-azido ketones 115 with pyridinium ylides 114 using oxygen as a green oxidant (Scheme 40). The oxo-functionality present in α-azido ketones increased its acidity thus making it a good organic synthon. Optimization of the reaction conditions revealed

• heterocycles. Pyridinium ylides used as 1,3-dipoles in this protocol were synthesized by the reaction of pyridines with α-bromo ketones (Scheme 41). The protocol was applicable to a series of EW and EDGs on phenacyl azides. However, the reaction was not successful with ethyl azidoacetate. On the other hand, EW

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

• (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

• high degree of delocalization into the neighboring phenyl group. Both the trication 3 and the tetracation 4 were directly observed from FSO3H–SbF5 solution using low temperature NMR. Experimental observations also revealed an exceptionally high acidity of the pyridinium N–H bonds. Here, we describe the

• position and deprotonation of the para-carbon to complete the arylation step. For the cyclization product 11, theoretical calculations indicate that cyclization requires deprotonation at the pyridinium ring [11]. Thus, either the tetracation 15 or the pentacation 16 is the likely precursor to the pyrido

Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response

• Yu-Ying Wang,
• Yong Kong,
• Zhe Zheng,
• Wen-Chao Geng,
• Zi-Yi Zhao,
• Hongwei Sun and
• Dong-Sheng Guo

Beilstein J. Org. Chem. 2019, 15, 1394–1406, doi:10.3762/bjoc.15.139

• the dissolved pyridinium-N-phenoxidebetaine dye in a solvent, measured in kcal mol−1 [47]. The linear relationship between the maximum emission wavenumbers (ν̃, cm−1) and ET(30) for 2,6-TNS [ν̃ = −256ET(30) + 36431.5, R2 = 0.963] and 1.8-ANS [ν̃ = −159.8ET(30) + 29602.9, R2 = 0.986] were established

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

• selectivities; they have demonstrated excellent complex ability towards inorganic cations, organic ammonium cations, pyridinium guests, neutral molecules (alcohols, ketones, nitriles), dye molecules, etc. [26]. p-Sulfonatocalix[n]arenes are complexing agents for structurally diverse biologically active

Electrophilic oligodeoxynucleotide synthesis using dM-Dmoc for amino protection

• Shahien Shahsavari,
• Dhananjani N. A. M. Eriyagama,
• Bhaskar Halami,
• Vagarshak Begoyan,
• Marina Tanasova,
• Jinsen Chen and
• Shiyue Fang

Beilstein J. Org. Chem. 2019, 15, 1116–1128, doi:10.3762/bjoc.15.108

• hydrophobic than the desired full-length sequence. Another consideration was that with acetic anhydride for capping, chances existed for replacing the dM-Dmoc groups with acetyl group during capping due to the presence of acids such as pyridinium acetate and large excess of acetic anhydride. Once the capping