Synthesis and metal binding properties of N-alkylcarboxyspiropyrans

• Alexis Perry and
• Christina J. Kousseff

Beilstein J. Org. Chem. 2017, 13, 1542–1550, doi:10.3762/bjoc.13.154

• previously reported [28]. Presumably, this reaction proceeds via azomethine ylid 6 (Scheme 3); analogous indolium ylids have been used synthetically in 1,3-dipolar cycloadditions [29] and mechanistic studies have been published on the related decarboxylation of pyridinium 2-carboxylates [30]. Fortunately, α

Synthesis of oligonucleotides on a soluble support

• Harri Lönnberg

Beilstein J. Org. Chem. 2017, 13, 1368–1387, doi:10.3762/bjoc.13.134

• linker by 5 mmol L−1 K2CO3 in a 3:43:10 mixture of DCM, dioxane and MeOH (30 min), followed by neutralization with pyridinium chloride, left the 5´-O-DMTr group, 2-chlorophenyl phosphate protections and base moiety protections untouched. Silica gel chromatographic purification and conventional

Synthesis of tetrasubstituted pyrazoles containing pyridinyl substituents

• Josef Jansa,
• Ramona Schmidt,
• Ashenafi Damtew Mamuye,
• Laura Castoldi,
• Alexander Roller,
• Vittorio Pace and
• Wolfgang Holzer

Beilstein J. Org. Chem. 2017, 13, 895–902, doi:10.3762/bjoc.13.90

• the pyridine nitrogens of the azine ring attached to pyrazole N-1 are somewhat smaller than those of the corresponding pyridine N-atoms in systems attached to pyrazole C-3, C-5 (or C-4), whereas the C-3-pyridine nitrogen atom in many cases was the most deshielded one. The pyridinium-type nitrogen (N-6

New approach toward the synthesis of deuterated pyrazolo[1,5-a]pyridines and 1,2,4-triazolo[1,5-a]pyridines

• Aleksey Yu. Vorob’ev,
• Vyacheslav I. Supranovich,
• Gennady I. Borodkin and
• Vyacheslav G. Shubin

Beilstein J. Org. Chem. 2017, 13, 800–805, doi:10.3762/bjoc.13.80

• treating asthma and post-stroke patients [16]. 1,2,4-Triazolo[1,5-a]pyridines show antifungal [17], antitumor [18], and cytotoxic [19] activities. Both types of heterocyclic cores are readily available from N-aminopyridium salts and related pyridinium-N-imines via 1,3-cycloaddition reaction [20] or

• intramolecular ring closure [21][22][23][24]. The importance of these cores for medical chemistry studies suggests that isotopically labeled pyrazolo[1,5-a]pyridines and triazolo[1,5-a]pyridines could be of interest. Recently, deuterium-labeled pyridinium-N-imines were applied to mechanistic studies of the

• different positions of pyridinium cations we carried out DFT calculations [31] at the M06-2X 6-31+G(d,p) [32] level of theory with SMD [33] solvation (Figure 1, see also Supporting Information File 1). As expected, in all cases the NH2 group is the most acidic. The NH2 group is usually ≈12–13 pKa units more

Synthesis of D-manno-heptulose via a cascade aldol/hemiketalization reaction

• Yan Chen,
• Xiaoman Wang,
• Junchang Wang and
• You Yang

Beilstein J. Org. Chem. 2017, 13, 795–799, doi:10.3762/bjoc.13.79

• ). The reaction of 5 with ethanethiol in the presence of hydrochloric acid followed by selective protection of the 4,5-diol with 2,2-dimethoxypropane using pyridinium p-toluenesulfonate as the promoter gave the 4,5-O-isopropylidene derivative 6 in 71% yield over two steps [40]. Treatment of diol 6 with

The reductive decyanation reaction: an overview and recent developments

• Jean-Marc R. Mattalia

Beilstein J. Org. Chem. 2017, 13, 267–284, doi:10.3762/bjoc.13.30

• in situ by deprotonation with KHMDS of its pyridinium ion precursor 79 in refluxing toluene (method B). With method B, malononitriles are reduced to mononitriles with comparable yields to that achieved with photoactivated 78 (73k,m,n). No allylic bond cleavage is observed and alkene moieties are

Interactions between photoacidic 3-hydroxynaphtho[1,2-b]quinolizinium and cucurbit[7]uril: Influence on acidity in the ground and excited state

• Jonas Becher,
• Daria V. Berdnikova,
• Darinka Dzubiel,
• Heiko Ihmels and
• Phil M. Pithan

Beilstein J. Org. Chem. 2017, 13, 203–212, doi:10.3762/bjoc.13.23

• )pyridine (3) [43] with 2-methoxy-6-bromomethylnaphthalene (4) [44] gave the corresponding (naphthylmethyl)pyridinium bromide 5 in 62% yield. Subsequent treatment of this intermediate with aq HBr (48%) led to acid-catalyzed cyclization and elimination of water, as well as to demethylation of the ether group

• ]. Notably, the chromophore of the oxyanion-substituted quinolizinium derivative 2cB resembles the well-established solvatochromic pyridinium-N-phenolate betaine dyes that are employed as polarity probes [53]. Correspondingly, the derivative 2cB shows a similar positive solvatochromism, i.e., a blue shift of

• , Flawil, CH); uncorrected. Synthesis 2-(1,3-Dioxolan-2-yl)-1-[(6-methoxynaphth-2-yl)methyl]pyridinium bromide (5). Under argon-gas atmosphere, a solution of 2-(1,3-dioxolan-2-yl)pyridine (3) [43] (1.83 g, 12.1 mmol) and 6-methoxy-2-bromomethylnaphthalene (4) [44] (3.05 g, 12.1 mmol) in DMSO (90 mL) was

A postsynthetically 2’-“clickable” uridine with arabino configuration and its application for fluorescent labeling and imaging of DNA

• Heidi-Kristin Walter,
• Bettina Olshausen,
• Ute Schepers and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2017, 13, 127–137, doi:10.3762/bjoc.13.16

• . In D1 and D2, the pyridinium part is connected to the rest of the dye by its 4-position, in D3 and D4 via its 2-position. The latter connectivity has a larger stabilizing influence on the DNA2a double strands. The fluorescence quantum yields of dsDNA2a are all higher than the corresponding ones of

New approaches to organocatalysis based on C–H and C–X bonding for electrophilic substrate activation

• Pavel Nagorny and
• Zhankui Sun

Beilstein J. Org. Chem. 2016, 12, 2834–2848, doi:10.3762/bjoc.12.283

• attributed to their ability to form a hydrogen bond with the oxygen of epoxide. In 2015 Shirakawa and Maruoka demonstrated that ammonium salts L5 and L6 could serve as effective catalysts for isoquinolinium and pyridinium salt Mannich reactions (Scheme 7) [50]. Catalysts L5 and L6 were selected due to their

• -workers reported the use of N-alkylated 3,5-di(carbomethoxy)pyridinium ions L13 to catalyze the reaction between 1-chloroisochroman and silyl ketene acetals (Scheme 10A). Catalyst L13 with R3 = C6F5 was found to be particularly active, and was found to efficiently form the product at 2 mol % loading

• propose that catalysts L13 could act not only through Coulombic interactions, but also as hydrogen bond donors. While various factors including Coulombic interactions between the pyridinium (or ammonium) salt and the chloride undoubtedly play an important role in promoting substrate ionization and

Sydnone C-4 heteroarylation with an indolizine ring via Chichibabin indolizine synthesis

• Florin Albota,
• Mino R. Caira,
• Constantin Draghici,
• Florea Dumitrascu and
• Denisa E. Dumitrescu

Beilstein J. Org. Chem. 2016, 12, 2503–2510, doi:10.3762/bjoc.12.245

• Pharmacy, University Ovidius, Aleea Universitatii 1, Constantza, Romania 10.3762/bjoc.12.245 Abstract The synthesis of sydnones heteroarylated at C-4 with an indolizine was achieved by Chichibabin (Tschitschibabin) indolizine synthesis starting from the corresponding sydnone-N-pyridinium bromides. The

• ; Chichibabin synthesis; indolizine; pyridinium N-ylide; sydnone; Introduction In recent decades, interest in the syntheses of biheteroaryls has been focused on the creation of new hetaryl–hetaryl C(sp2)–C(sp2) bonds, in particular through cross-coupling reactions. These reactions are catalyzed by palladium or

• pyridinium salts used in the indolizine Chichibabin synthesis. Results and Discussion In order to obtain the compounds 4 containing an indolizine ring attached directly to the C-4 carbon atom of a sydnone ring (i.e., indolizination of sydnones at C-4), the Chichibabin indolizine synthesis was employed. The

A new protocol for the synthesis of 4,7,12,15-tetrachloro[2.2]paracyclophane

• Donghui Pan,
• Yanbin Wang and
• Guomin Xiao

Beilstein J. Org. Chem. 2016, 12, 2443–2449, doi:10.3762/bjoc.12.237

• in the bromination process [10][11][12]. In addition, the release of corrosive HBr as a byproduct and the use of organic solvents make this protocol less environmentally friendly [13]. The use of other brominating agents, such as N-bromosuccinimide (NBS) and pyridinium tribromides, also has the

Elongated and substituted triazine-based tricarboxylic acid linkers for MOFs

• Arne Klinkebiel,
• Ole Beyer,
• Barbara Malawko and
• Ulrich Lüning

Beilstein J. Org. Chem. 2016, 12, 2267–2273, doi:10.3762/bjoc.12.219

• improve the yield, a methoxy cleaving procedure which has been found to be effective in other demanding demethylations [24] was used. In liquid pyridinium chloride (which melts at 144 °C), apparently all intermediates were sufficiently soluble and consequently all four methoxy groups of 16c could be

• from the methoxy-substituted triester 19c. As successfully applied for 16c, molten pyridinium chloride was used as the cleaving reagent and all four methoxy groups of 19c could be cleaved leading to the hydroxy-substituted triacid 20e in 62% yield. All three triacids 20a, b and e precipitate from water

• , 60 °C, quant., d) pyridinium hydrochloride, 12 h, 200 °C, 17e: 52%. Triple Suzuki coupling between tribromotriazines 3 and boronate 18. Conditions: a) 19a: Pd(PPh3)4, K3PO4, dioxane/H2O, 2 d, 120 °C, 24%; 19b: Pd(dppf)Cl2, K3PO4, dioxane/H2O, 3 d, 120 °C, 16%; 19c: Pd(PPh3)4, K3PO4, dioxane/H2O, 2 d

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