The direct oxidative diene cyclization and related reactions in natural product synthesis

• Juliane Adrian,
• Leona J. Gross and
• Christian B. W. Stark

Beilstein J. Org. Chem. 2016, 12, 2104–2123, doi:10.3762/bjoc.12.200

• linear precursor 84 was cyclized diastereoselectively to the mono-THF intermediate 85 with an oxorhenium(VII) complex and was subsequently subjected to the second oxidative cyclization using stoichiometric amounts of pyridinium chlorochromate (PCC) to give the bis-THF compound 86, which was easily

Ionic liquids as transesterification catalysts: applications for the synthesis of linear and cyclic organic carbonates

• Maurizio Selva,
• Alvise Perosa,
• Sandro Guidi and
• Lisa Cattelan

Beilstein J. Org. Chem. 2016, 12, 1911–1924, doi:10.3762/bjoc.12.181

• screening guide. IL-based catalysts for transesterification reactions Synthesis of IL-catalysts: IL-based catalysts for transesterification reactions mostly comprise imidazolium, phosphonium, ammonium, sulfonium and pyridinium salts. The conventional syntheses of such compounds usually start from the

• with respect to traditional homogenous systems in terms of milder reaction conditions and easier separation and recycle workups. Two representative examples of ionic liquids employed for the synthesis of FAMEs are the pyridinium and oxazolidinone-based compounds shown in Figure 2 [52][53]. It should be

Mutagenic activity of quaternary ammonium salt derivatives of carbohydrates

• Barbara Dmochowska,
• Karol Sikora,
• Anna Woziwodzka,
• Jacek Piosik and
• Beata Podgórska

Beilstein J. Org. Chem. 2016, 12, 1434–1439, doi:10.3762/bjoc.12.138

• using two different techniques: The Vibrio harveyi luminescence assay and the Ames test. The obtained results support previous findings contesting QAS safety and indicate that QAS, specifically pyridinium derivatives, might be mutagenic. Keywords: 6-bromohexyl D-glucopyranoside; microbiological

• the Vibrio luminescence assay at all. Apart from N-[6-(β-D-glucopyranosyloxy)hexyl]-N,N,N-trimethylammonium bromide (5a), pyridinium salts tend to be more mutagenic than their trimethylammonium counterparts. Moreover, the position of the hexyl chain occurs to be important for mutagenicity of

• assay. Obtained results suggest that at least some of QASs can be genotoxic. Moreover, we observed that pyridinium salts tend to be more mutagenic than trimethylammonium derivatives, whereas the position of the hexyl chain seems to be important for the extent of the mutagenic activity of

The synthesis of functionalized bridged polycycles via C–H bond insertion

• Jiun-Le Shih,
• Po-An Chen and
• Jeremy A. May

Beilstein J. Org. Chem. 2016, 12, 985–999, doi:10.3762/bjoc.12.97

• generated from alkynes can produce bridged bicycles from C–H bond insertion (Scheme 23) [96]. This was first implemented by transannular insertion via 107 to give the bicyclo[3.2.1]octane 108. The diastereoselectivity of the process was not reported. Again, dual gold catalysts were used with a pyridinium

Mycothiol synthesis by an anomerization reaction through endocyclic cleavage

• Shino Manabe and
• Yukishige Ito

Beilstein J. Org. Chem. 2016, 12, 328–333, doi:10.3762/bjoc.12.35

• (dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxid hexafluorophosphate (HATU) [23][24], we found that purification of the product was rather difficult, especially for >50 mg-scale reactions. The reason for the low yield is probably the low solubility of the product in the reported solvent system

Interactions of cyclodextrins and their derivatives with toxic organophosphorus compounds

• Sophie Letort,
• Sébastien Balieu,
• William Erb,
• Géraldine Gouhier and
• François Estour

Beilstein J. Org. Chem. 2016, 12, 204–228, doi:10.3762/bjoc.12.23

• acids on one C-6 position [76]. Efficiency of compounds 20a–e against chemical warfare agents: The authors demonstrated the high activity of the pyridinium derivatives, especially the compounds 20b and 20d, against cyclosarin (Scheme 4). Indeed, the nerve agent was totally hydrolyzed in less than five

• , the less active compound is the weak acid oxime derivative 20a. Then, the formation of the more nucleophilic aldoximate is favored with the pyridinium derivatives 20b–d, explaining their high activity. The moderate efficiency of ketoximes 20d and 20e, compared to that of the corresponding aldoximes

• 20b and 20c, strengthen this hypothesis. Finally, the para-substituted pyridinium derivative 20c is much less reactive than the meta compound 20b. This tends to prove that even slight structural differences have a major impact on the hydrolytic reactivity of the cyclodextrin. Based on these results

Effective immobilisation of a metathesis catalyst bearing an ammonium-tagged NHC ligand on various solid supports

• Krzysztof Skowerski,
• Jacek Białecki,
• Stefan J. Czarnocki,
• Karolina Żukowska and
• Karol Grela

Beilstein J. Org. Chem. 2016, 12, 5–15, doi:10.3762/bjoc.12.2

• and circulating flow reactor, as well as in an industrial setup [30][31]. The concept was explored further, and a pyridinium-tagged complex deposited on modified silica gel was recently obtained by Kirschning, Mauduit et al., exhibiting much better activity and efficiency than 4 [32]. Specially

Enantioselective additions of copper acetylides to cyclic iminium and oxocarbenium ions

• Jixin Liu,
• Srimoyee Dasgupta and
• Mary P. Watson

Beilstein J. Org. Chem. 2015, 11, 2696–2706, doi:10.3762/bjoc.11.290

• polystyrene bead through the C7 hydroxy group. In 2007, Ma and co-workers reported the first enantioselective, copper-catalyzed alkynylation of a pyridinium ion (Scheme 6) [26]. This reaction employs an N-acylpyridinium ion generated in situ and a CuI/Indabox catalyst. Ma found that the identity of base and

Syntheses of 2-substituted 1-amino-4-bromoanthraquinones (bromaminic acid analogues) – precursors for dyes and drugs

• Enas M. Malik,
• Younis Baqi and
• Christa E. Müller

Beilstein J. Org. Chem. 2015, 11, 2326–2333, doi:10.3762/bjoc.11.253

• was subsequently used to prepare the corresponding 2-carbaldehyde 7, the 2-carboxylic acid 8, and the 2-cyano derivative 9 under the following reaction conditions. Treatment of compound 6 with pyridinium chlorochromate in dichloromethane afforded carbaldehyde 7. Potassium permanganate was used as the

Beyond catalyst deactivation: cross-metathesis involving olefins containing N-heteroaromatics

• Kevin Lafaye,
• Cyril Bosset,
• Lionel Nicolas,
• Amandine Guérinot and
• Janine Cossy

Beilstein J. Org. Chem. 2015, 11, 2223–2241, doi:10.3762/bjoc.11.241

• metathesis Formation of pyridinium/imidazolium salt prior to metathesis Most of the examples of RCM involving substrates that possess a pyridine ring relied on the pre-requisite formation of a pyridinium salt. In 2004, Vaquero et al. reported the synthesis of dihydroquinolizium cations through RCM of dienic

• pyridinium salts in the presence of the GII catalyst (Scheme 11) [47]. The formation of seven- and eight-membered rings required high dilution. Few years later, the same authors showed that it was possible to oxidize 3,4-dihydroquinolizinium salts into their quinolizinium counterparts using Pd/C at high

• -induced decomposition of GII in RCM conditions. Deactivation of methylidene 2 in the presence of pyridine. Reaction of G-HII with various amines. Formation of olefin 22 from styrene. Hypothetic deactivation pathway of G-HII. RCM of dienic pyridinium salts. Synthesis of polycyclic scaffolds using RCM

The marine sponge Agelas citrina as a source of the new pyrrole–imidazole alkaloids citrinamines A–D and N-methylagelongine

• Christine Cychon,
• Ellen Lichte and
• Matthias Köck

Beilstein J. Org. Chem. 2015, 11, 2029–2037, doi:10.3762/bjoc.11.220

• ) which consist of a pyridinium ring and an ester linkage instead of the aminoimidazole moiety and the common amide bond in PIAs. Keywords: Agelas citrina; marine sponges; mauritiamine; NMR; pyrrole–imidazole alkaloids; Introduction The family of pyrrole-imidazole alkaloids (PIAs) represents a

• pyrrole–pyridinium alkaloid N-methylagelongine (5) was also isolated from Agelas citrina. Compound 5 is the N-methylated pyrrole derivative of agelongine (12). The debromo compound is known as daminin (21). The citrinamines A–D (1–4) were tested against several pathogenic bacteria, fungi, and cultures of

The simple production of nonsymmetric quaterpyridines through Kröhnke pyridine synthesis

• Isabelle Sasaki,
• Jean-Claude Daran and
• Gérard Commenges

Beilstein J. Org. Chem. 2015, 11, 1781–1785, doi:10.3762/bjoc.11.193

• 3 as the masked enone. Pure compound 3 was only obtained in the presence of an excess of Eschenmoser’s salt, by addition of 2 equiv of (N,N-dimethyl)methyliminium chloride to 1, in acetonitrile at room temperature. Then, compound 3 was condensed with N-[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide

• accomplished through the simple synthesis of 6-acetyl-2,2’:6’,2”-terpyridine. After the preparation of the corresponding pyridinium salt, the subsequent condensation with enones led to the desired quaterpyridines. The methyl groups on the pyridine ring are potential grafting points, which can be used without

Pyridinoacridine alkaloids of marine origin: NMR and MS spectral data, synthesis, biosynthesis and biological activity

• Louis P. Sandjo,
• Victor Kuete and
• Maique W. Biavatti

Beilstein J. Org. Chem. 2015, 11, 1667–1699, doi:10.3762/bjoc.11.183

• imine formation and aromatization, occurred presumably due to the presence of an acidic solvent. Styelsamine B (4) was obtained with an overall yield of 35%. This pyridinium salt was treated with an ampholyte to afford its neutral form cystodytin J (Scheme 1) [58]. This biomimetic synthetic strategy is

Fates of imine intermediates in radical cyclizations of N-sulfonylindoles and ene-sulfonamides

• Hanmo Zhang,
• E. Ben Hay,
• Stephen J. Geib and
• Dennis P. Curran

Beilstein J. Org. Chem. 2015, 11, 1649–1655, doi:10.3762/bjoc.11.181

• -iodoaniline, PPTS (pyridinium p-toluenesulfonate) and NaBH4 (64%) was followed by N-acylation of the aniline nitrogen atom (80%) provided the target precursor 10. The reaction of 7 with 1 equiv of tributyltin hydride was incomplete, but the use of 2.5 equiv of tributyltin hydride at fixed concentration ([7

Grubbs–Hoveyda type catalysts bearing a dicationic N-heterocyclic carbene for biphasic olefin metathesis reactions in ionic liquids

• Maximilian Koy,
• Hagen J. Altmann,
• Benjamin Autenrieth,
• Wolfgang Frey and
• Michael R. Buchmeiser

Beilstein J. Org. Chem. 2015, 11, 1632–1638, doi:10.3762/bjoc.11.178

• –alkylidene-triggered metathesis-based polymerizations, Ru contamination was very low (<2.5 ppm) and even outrivals earlier reported systems bearing two pyridinium carboxylates by at least a factor of 10 [14]. Clearly, both the initiator and any Ru-containing decomposition products selectively stay in the IL

Latent ruthenium–indenylidene catalysts bearing a N-heterocyclic carbene and a bidentate picolinate ligand

• Thibault E. Schmid,
• Florian Modicom,
• Adrien Dumas,
• Etienne Borré,
• Loic Toupet,
• Olivier Baslé and
• Marc Mauduit

Beilstein J. Org. Chem. 2015, 11, 1541–1546, doi:10.3762/bjoc.11.169

• improve the synthesis efficiency of the desired complex 4a, the [(SIPr)RuCl2(indenylidene)pyridine] complex 5 was used as a precursor (Scheme 2). The latter species offers both the advantages to avoid the use of phosphine scavenger and to trap the acid formed as a pyridinium chloride salt. Gratifyingly

Synthesis of a tricyclic lactam via Beckmann rearrangement and ring-rearrangement metathesis as key steps

• Sambasivarao Kotha,
• Ongolu Ravikumar and
• Jadab Majhi

Beilstein J. Org. Chem. 2015, 11, 1503–1508, doi:10.3762/bjoc.11.163

• ]. Results and Discussion To begin with, the oxidation of dicyclopentadiene (5) in the presence of SeO2 gave 1α-dicyclopentadienol (6), which on treatment with pyridinium chlorochromate (PCC) [31] delivered the known tricyclic enone 4. Selective reduction of enone 4 with Zn in AcOH/EtOH under reflux

Pyridine-promoted dediazoniation of aryldiazonium tetrafluoroborates: Application to the synthesis of SF₅-substituted phenylboronic esters and iodobenzenes

• George Iakobson,
• Junyi Du,
• Alexandra M. Z. Slawin and
• Petr Beier

Beilstein J. Org. Chem. 2015, 11, 1494–1502, doi:10.3762/bjoc.11.162

• tetrafluoroborates and suggested the formation of diazopyridinium salts which homolytically decompose to aryl radicals, nitrogen and a pyridinium tetrafluoroborate radical [79][80]. Tanaka and co-workers have used the combination of PhN2+BF4− and pyridine for arylations of silylenol ethers [81]. They have observed

• aryldiazopyridinium 4 which decomposes to an aryl radical, a pyridinium tetrafluoroborate radical and nitrogen. The aryl radical reacts with B2pin2 to form the borylated product 2 and the Bpin radical (likely to be stabilized by pyridine) [82]. The byproducts pyridine·BF3 and F-Bpin are formed by the reaction of the

• pyridinium tetrafluoroborate radical and the Bpin radical. Subjecting the diazonium salt 3i to the borylation conditions gave further indirect evidence for the formation of aryl radicals (Scheme 3). Full conversion of 3i was observed affording a mixture of products 2i, 2i’, 5i (two isomers of unknown

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

• treated with LAH to generate diol 266 (72–92%). The dehydration of diol 266 with pyridinium p-toluenesulfonate in benzene gave diolefin 267. [2 + 2] Photocycloaddition of diolefin 267 was carried out by irradiation with a 400 W high-pressure Hg lamp (Pyrex filter) in benzene for 26–92 h. After evaporation

Indolizines and pyrrolo[1,2-c]pyrimidines decorated with a pyrimidine and a pyridine unit respectively

• Marcel Mirel Popa,
• Emilian Georgescu,
• Mino R. Caira,
• Florentina Georgescu,
• Constantin Draghici,
• Raluca Stan,
• Calin Deleanu and
• Florea Dumitrascu

Beilstein J. Org. Chem. 2015, 11, 1079–1088, doi:10.3762/bjoc.11.121

• corresponding cycloimmonium bromides. In the case of 4-(3-pyridyl)pyrimidine and 4-(4-pyridyl)pyrimidine the quaternization reactions occur as expected at the pyridine nitrogen atom leading to pyridinium bromides and consequently to new indolizines via the corresponding pyridinium N-ylides. However, in the case

• bromide salts was performed and will be discussed in each case. In the case of pyridinium ylides generated from 4-(3-pyridyl)pyrimidine (7), new indolizines 14a–f decorated with a pyrimidine moiety were obtained (Scheme 2). The reaction appears to be selective towards the indolizines 14. In some cases the

• group induces a shielding effect on the C-1 atom from 115 ppm in the case of 14a, to 104.8–108.1 ppm for 14b–f. Similarly, in the case of pyridinium N-ylides generated from 8, the new indolizines 16 were synthesized (Scheme 3) and structurally characterized. Again, in the case of some compounds, the

Synthesis of multivalent carbohydrate mimetics with aminopolyol end groups and their evaluation as L-selectin inhibitors

• Joana Salta,
• Jens Dernedde and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2015, 11, 638–646, doi:10.3762/bjoc.11.72

• selected HATU (1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium-3-oxide hexafluorophosphate), a coupling reagent frequently used in peptide synthesis [34]. We applied standard conditions for the preparation of one divalent and two trivalent amides (Scheme 4). To our pleasure divalent

Novel stereocontrolled syntheses of tashiromine and epitashiromine

• Loránd Kiss,
• Enikő Forró and
• Ferenc Fülöp

Beilstein J. Org. Chem. 2015, 11, 596–603, doi:10.3762/bjoc.11.66

• the indolizidine framework; access to tashiromine in racemic form can be achieved through the alkylation of succinimide, followed by ring closure via acyliminium intermediates [23][24], the reduction of cyclized pyridinium salts [25], iminium cascade cyclization [26], alkyne-mediated hydroformylation

The reactions of 2-ethoxymethylidene-3-oxo esters and their analogues with 5-aminotetrazole as a way to novel azaheterocycles

• Marina V. Goryaeva,
• Yanina V. Burgart,
• Marina A. Ezhikova,
• Mikhail I. Kodess and
• Viktor I. Saloutin

Beilstein J. Org. Chem. 2015, 11, 385–391, doi:10.3762/bjoc.11.44

• substitution. The use of diethyl 2-ethoxymethylidenemalonate in this reaction resulted in ethyl 7-hydroxytetrazolo[1,5-a]pyrimidine-6-carboxylate, while ethyl 2-ethoxymethylidenecyanoacetate yielded 5-[2,6-diamino-3,5-bis(ethoxycarbonyl)pyridinium-1-yl]tetrazol-1-ide through an alternative pathway. Ethyl 2

• to conclude that the molecule of compound 11 is symmetric and bears one methine proton, two amino groups and two ethoxycarbonyl substituents. The final structure of compound 11 as 5-[2,6-diamino-3,5-bis(ethoxycarbonyl)pyridinium-1-yl]tetrazol-1-ide was confirmed by X-ray diffraction (Figure 2). The

Properties of cationic monosubstituted tetraalkylammonium cyclodextrin derivatives – their stability, complexation ability in solution or when deposited on solid anionic surface

• Martin Popr,
• Sergey K. Filippov,
• Nikolai Matushkin,
• Juraj Dian and
• Jindřich Jindřich

Beilstein J. Org. Chem. 2015, 11, 192–199, doi:10.3762/bjoc.11.20

• CD polymers, where the CD units are randomly crosslinked by suitable reagents. Systems for separation of gases, composed of cationic CD pyridinium polymer and a Nafion® membrane were reported by Grossi and coworkers [24]. The Kusumocahyo group studied separation abilities of cationic CD copolymers

Synthesis of dinucleoside acylphosphonites by phosphonodiamidite chemistry and investigation of phosphorus epimerization

• William H. Hersh

Beilstein J. Org. Chem. 2015, 11, 184–191, doi:10.3762/bjoc.11.19

• triflate as the activator to give the monoamidites 3′-O-(P(N(iPr)2)C(O)R)-5′-O-DMTr-thymidine, and further coupling with 3′-O-(tert-butyldimethylsilyl)thymidine was carried out with activation by pyridinium trifluoroacetate/N-methylimidazole. The new dinucleoside acylphosphonites could be further oxidized

• both 10 and 11 in the 1H and 13C NMR spectra. Since this was not relevant to phosphorus epimerization, it was not further investigated. Dinucleoside coupling was carried out using the 2:1 pyridinium trifluoroacetate/N-methylimidazole (PTFA/NMI) activator developed at Isis to combine phosphonamidites 10