Site-selective reactions mediated by molecular containers

• Rui Wang and
• Yang Yu

Beilstein J. Org. Chem. 2022, 18, 309–324, doi:10.3762/bjoc.18.35

• ) [60]. The host in here was a water-soluble deep cavitand D with methylated urea groups on the rim, which had already been used to mediate other organic reactions [61]. The feet of the host were transformed to pyridinium cationic moieties to make it soluble in water, and in other examples, similar

Synthetic strategies toward 1,3-oxathiolane nucleoside analogues

• Umesh P. Aher,
• Dhananjai Srivastava,
• Girij P. Singh and
• Jayashree B. S

Beilstein J. Org. Chem. 2021, 17, 2680–2715, doi:10.3762/bjoc.17.182

• . Reaction of 24 with pyridinium dichromate (PDC) in DMF solvent afforded the acid derivative 25. This derivative was converted to the key intermediate 20 by oxidative decarboxylation [33]. Han et al. [43] developed a method for the novel oxathiolane intermediate 2-(tert-butyldiphenylsilyloxy)methyl-5

Direct C(sp³)–H allylation of 2-alkylpyridines with Morita–Baylis–Hillman carbonates via a tandem nucleophilic substitution/aza-Cope rearrangement

• Siyu Wang,
• Lianyou Zheng,
• Shutao Wang,
• Shulin Ning,
• Zhuoqi Zhang and
• Jinbao Xiang

Beilstein J. Org. Chem. 2021, 17, 2505–2510, doi:10.3762/bjoc.17.167

• pyridinium cation intermediate A. The in situ generated tert-butoxide anion has enough basicity to deprotonate of the activated benzylic proton of intermediate A and generates the anion B1, which can be tautomerized into more stable enamine intermediate B2. Finally, the intermediates B1 or B2 occur an

Halides as versatile anions in asymmetric anion-binding organocatalysis

• Lukas Schifferer,
• Martin Stinglhamer,
• Kirandeep Kaur and
• Olga García Macheño

Beilstein J. Org. Chem. 2021, 17, 2270–2286, doi:10.3762/bjoc.17.145

• catalysts and asymmetric methodologies, a few innovative nonchiral alternative H-donor or halide-binding organocatalysts, like, e.g., tridentate phosphoramides [41], onium salts [42] such as Berkessel's pyridinium systems [43], or Huber's bis-iodo imidazolium [44] and neutral bridged 2,6-diiodo‐3,4,5

• [86]. Besides the contact to the chloride anion, investigations with tetrabutylammonium chloride (TBACl) and pyridinium chloride salt as model compounds found evidence for productive interactions between the catalyst and the cations. However, these interactions may not solely be attributed to cation–π

Constrained thermoresponsive polymers – new insights into fundamentals and applications

• Patricia Flemming,
• Alexander S. Münch,
• Andreas Fery and
• Petra Uhlmann

Beilstein J. Org. Chem. 2021, 17, 2123–2163, doi:10.3762/bjoc.17.138

• concentration of the polymer, but also by the nature of the anion as well as its concentration. Moreover, UCST behavior induced by BF4− was also detected in aqueous solutions of polypeptides, whose side chains contain charged pyridinium or imidazolium functionalities [290][291]. In contrast to single charged

Development of N-F fluorinating agents and their fluorinations: Historical perspective

• Teruo Umemoto,
• Yuhao Yang and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2021, 17, 1752–1813, doi:10.3762/bjoc.17.123

• on the pyridinium nuclei, and were the first reactive, easy-to-handle fluorinating agents with wide application [28][29]. The work continued with additional disclosures until 1991 [30][31][32][33][34]. Before that, reactive fluorinating reagents were difficult to handle because of toxicity, a

• reagents as illustrated in Scheme 9 [28]. Moreover, they found that the fluorination power (reactivity) of these N-fluoropyridinium salts could be tuned by the substituents on the pyridinium nuclei. The transformation of the unstable pyridine·F2 complex to stable N-fluoropyridinium salts could be conducted

• observations are noted: N-Fluoro-2,6-bis(methoxymethyl)pyridinium triflate (5-4l) fluorinated the trimethylsilyl ether of γ-butyrolactone and 1-cyclohexenyl acetate in much higher yields than the N-fluoro-2,4,6-trimethyl salt 5-4j [32]. Thus, as seen in Scheme 13, 5-4l converted the Corey lactone 5-7 via its

Chemical approaches to discover the full potential of peptide nucleic acids in biomedical applications

• Nikita Brodyagin,
• Martins Katkevics,
• Venubabu Kotikam,
• Christopher A. Ryan and
• Eriks Rozners

Beilstein J. Org. Chem. 2021, 17, 1641–1688, doi:10.3762/bjoc.17.116

Free-radical cyclization approach to polyheterocycles containing pyrrole and pyridine rings

• Ivan P. Mosiagin,
• Olesya A. Tomashenko,
• Dar’ya V. Spiridonova,
• Mikhail S. Novikov,
• Sergey P. Tunik and
• Alexander F. Khlebnikov

Beilstein J. Org. Chem. 2021, 17, 1490–1498, doi:10.3762/bjoc.17.105

• )-4-(ortho-iodophenyl)pyrrol-3-yl)pyridinium bromide makes it possible to obtain a monocyclization product, and the bicyclization product from the dibromo derivative. The procedure is also applicable to obtain 3-arylpyrido[2,1-a]pyrrolo[3,2-c]isoquinoline derivatives including 2-unsubstituted

• compounds are more expensive and less accessible than bromo-substituted analogs, we tried to accomplish the cyclization of pyridinium salt 1a using another radical mediator, tris(trimethylsilyl)silane (TTMSS) [31][32], which, moreover, is much less toxic than tributylstannane. Fortunately, free-radical

• developed protocol doesn’t require column chromatography for purification of target compounds 3 and can be performed in a gram scale. Pyridinium bromides 1a–l,n–w and iodide 1m were prepared by the reaction of 3-(2-bromophenyl)-2H-azirine (4a) with substituted N-phenacyl pyridinium salts 5a–w according to

Double-headed nucleosides: Synthesis and applications

• Vineet Verma,
• Jyotirmoy Maity,
• Vipin K. Maikhuri,
• Ritika Sharma,
• Himal K. Ganguly and
• Ashok K. Prasad

Beilstein J. Org. Chem. 2021, 17, 1392–1439, doi:10.3762/bjoc.17.98

• was reduced in the presence of NaBH4 followed by the treatment with MsCl in pyridine to get the nucleoside salt 129. Next, the pyridinium group was replaced by an N3-protected thymine in basic medium followed by removal of the protecting groups and the selective DMTr protection of the C-5′-hydroxy

N-tert-Butanesulfinyl imines in the asymmetric synthesis of nitrogen-containing heterocycles

• Joseane A. Mendes,
• Paulo R. R. Costa,
• Miguel Yus,
• Francisco Foubelo and
• Camilla D. Buarque

Beilstein J. Org. Chem. 2021, 17, 1096–1140, doi:10.3762/bjoc.17.86

• pyridinium p-toluenesulfonate (PPTS) also worked well to perform these condensations [1][16]. For the formation of aldimines, other methodologies are described in the literature using condensation reagents such as Yb(OTf)3 [17], Cs2CO3 [18] and KHSO4 [19]. However, for the synthesis of ketimines, Ti(OEt)4

• , indicating a mismatch between the chiral auxiliary and the stereocenter in this substrate. Concerning the oxidative cyclization reaction, pyridinium dichromate (PDC) provided low yields of expected lactam 77. Many oxidants were checked for this transformation to take place, and the Sarett reagent [CrO3·(C5H5

Enhanced target cell specificity and uptake of lipid nanoparticles using RNA aptamers and peptides

• Roslyn M. Ray,
• Anders Højgaard Hansen,
• Maria Taskova,
• Bernhard Jandl,
• Jonas Hansen,
• Citra Soemardy,
• Kevin V. Morris and
• Kira Astakhova

Beilstein J. Org. Chem. 2021, 17, 891–907, doi:10.3762/bjoc.17.75

• columns. Initially, fluorenylmethyloxycarbonyl (Fmoc) group removal from the Rink linker was achieved by applying 20% piperidine in DMF (2 × 30 min). Preactivation of Fmoc amino acid (4 equiv) prior each coupling was performed with 1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxide

Synthetic reactions driven by electron-donor–acceptor (EDA) complexes

• Zhonglie Yang,
• Yutong Liu,
• Kun Cao,
• Xiaobin Zhang,
• Hezhong Jiang and
• Jiahong Li

Beilstein J. Org. Chem. 2021, 17, 771–799, doi:10.3762/bjoc.17.67

• that could react with olefin 120 with an electron-withdrawing group to give alkylation product 121 under irradiation with light (Scheme 41). The reaction is compatible with various substrates, including alkenes, secondary alkylpyridinium ions, benzylic pyridinium ions, and primary alkylpyridinium ions

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