Search

Pyridinium 1,4-zwitterionic thiolates were applied to a formal [3 + 2] annulation reaction with modified activated alkynes, affording various tetrasubstituted thiophenes with aryl, alkenyl, alkyl or silyl group at the special position. The structural modification of alkyne substrates enabled the synthesis of diverse thiophenes to be achieved using the pyridinium 1,4-zwitterionic thiolates as the sulfur-containing building blocks. This approach is metal-free and catalyst-free.

A sterically strained ionic Bronsted pair complex obtained from a sterically bulky base 2,4,6-tri-tert-butylpyridine and hydrochloric acid imbues unusual reactivity to the anionic chloride. The complete shielding of the cationic [N-H]+ by the bulky ortho-tert-butyl groups weakens the possible hydrogen-bonding interactions with the chloride anion, and the [N-H]+···Cl- distance is unusually longer (3.10 A). This results in strained/frustrated electrostatic interactions between the ion-pair, thus infusing an increased reactivity in both of the ions, which results in the activation of a third molecule like thiol via hydrogen-bonding. This intriguing weak interaction-based reactivity has been utilized to develop an organocatalytic synthesis of 2-deoxy-β-thioglycosides from glycals. While the 1H NMR studies showcase the diamagnetic activation of thiols in the presence of the catalyst, the electron paramagnetic resonance (EPR) studies reveal the generation of a radical species that suggests a possible frustrated radical pair catalysis. Besides, IR spectroscopic studies explain the intriguing influence of size/charge density of the anion on the solvation-insusceptible, cationic [TTBPyH]+ and on the observed reactivity.

The ability of 4-[(benzyl­amino)­carbon­yl]-1-methyl­pyridinium to form iodide salts with cation:iodine ratio different from equimolar was studied and a Hirshfeld surface analysis was performed to investigate the inter­molecular inter­actions., The two iodide salts, 4-[(benzyl­amino)­carbon­yl]-1-methyl­pyridinium iodide–iodine (2/1), C14H15N2O+·I−·0.5I2, I, and 4-[(benzyl­amino)­carbon­yl]-1-methyl­pyridinium triiodide, C14H15N2O+·I3 −, II, with different cation:iodine atoms ratios were studied. Salt I contains one cation, one iodide anion and half of the neutral I2 mol­ecule in the asymmetric unit (cation:iodine atoms ratio is 1:2). Salt II contains two cations, one triiodide anion (I 3 −) and two half triiodide anions (cation:iodine atoms ratio is 1:3). The NH group forms N—H⋯I hydrogen bonds with the I− anion in the crystal of I or N—H⋯O hydrogen bonds in II where only triiodide anions are present.

The azomethine ylides are generally used in 1,3-dipolar cycloadditions with various dipolarophiles. In this work, a new and diverse route has been developed for the azomethine ylides, for synthesis of novel pyrrole derivatives. The azomethine ylide, produced via C–H activation of unreactive C(sp3)–H bond of 2-methylquinoline, by molecular iodine, in the presence of pyridine. Herein, we represent novel pyrrole derivatives, synthesized from the reaction of pyridinium ylide with olefins, which formed via a reaction of isatin, dialkyl acetylenedicarboxylate derivatives and pyridine as a base in moderate to excellent yields. Various features of this cyclization, discussed.

Upon addition of 5-15% PhNMe2H+X- (X = B(3,5-(CF3)2C6H3)4 or B(C6F5)4) to Mo(NAr)(styrene)(OSiPh3)2 (Ar = N-2,6-i-Pr2C6H3) in C6D6 an equilibrium mixture of Mo(NAr)(styrene)(OSiPh3)2 and Mo(NAr)(CMePh)(OSiPh3)2 is formed over 36 h at 45 °C (Keq = 0.36). A plausible intermediate in the interconversion of the styrene and 1-phenethylidene complexes is the 1-phenethyl cation, [Mo(NAr)(CHMePh)(OSiPh3)2]+, which can be generated using [(Et2O)2H][B(C6F5)4] as the acid. The interconversion can be modeled as two equilibria involving protonation of Mo(NAr)(styrene)(OSiPh3)2 or Mo(NAr)(CMePh)(OSiPh3)2 and deprotonation of the α or β phenethyl carbon atom in [Mo(NAr)(CHMePh)(OSiPh3)2]+. The ratio of the rate of deprotonation of [Mo(NAr)(CHMePh)(OSiPh3)2]+ by PhNMe2 in the α position versus the β position is ∼10, or ∼30 per Hβ. The slow step is protonation of Mo(NAr)(styrene)(OSiPh3)2 (k1 = 0.158(4) L/(mol·min)). Proton sources such as (CF3)3COH or Ph3SiOH do not catalyze the interconversion of Mo(NAr)(styrene)(OSiPh3)2 and Mo(NAr)(CMePh)(OSiPh3)2, while the reaction of Mo(NAr)(styrene)(OSiPh3)2 with pyridinium salts generates only a trace (∼2%) of Mo(NAr)(CMePh)(OSiPh3)2 and forms a monopyridine adduct, [Mo(NAr)(CHMePh)(OSiPh3)2(py)]+ (two diastereomers). The structure of [Mo(NAr)(CHMePh)(OSiPh3)2]+ has been confirmed in an X-ray study; there is no structural indication that a β proton is activated through a CHβ interaction with the metal. W(NAr)(CMePh)(OSiPh3)2 is also converted into a mixture of W(NAr)(CMePh)(OSiPh3)2 and W(NAr)(styrene)(OSiPh3)2 (Keq = 0.47 at 45 °C in favor of the styrene complex) with 10% [PhNMe2H][B(C6F5)4] as the catalyst; the time required to reach equilibrium is approximately the same as in the Mo system.

Three-component condensation of in situ generated pyridinium aroylmethylides with isatins or aromatic aldehydes and cyclic 1,3-dicarbonyl compounds gave a series of condensed 2-aroyl-2,3-dihydrofurans. The reaction proceeds diastereoselectively and represents a cascade process involving the Knoevenagel condensation, the carbo-Michael reaction, and intramolecular nucleophilic substitution. The possibility of reductive rearrangement of spirocyclic furanyl-substituted oxindole into a pyran derivative by the action of zinc in acetic acid was shown.

Aim: The design and synthesis of new molecules capable of forming self-assembled gels are indispensable to harvest new functional materials. Supramolecular gels have potential in many areas, particularly in biology and materials chemistry. Of the different types of applications, visual sensing of biologically relevant ionic analytes is a fairly recent trend. Here we describe naked-eye detection of fluoride ions involving sol-gel methodology. Methods: To execute this, cholesterol substituted pyridinium salts 1-4 have been designed and synthesized, of which compounds 3 and 4 served as potential gelators for the naked-eye detection of F- ions in DMSO and DMSO-H2O (1:1, v/v), respectively. Results: Addition of F- ions to the solutions of 3 and 4 in DMSO and DMSO: H2O (1:1, v/v) respectively, resulted in the formation of yellow and brown colored gels instantly at room temperature. Conclusion: Gelation study reveals that not only the aromatic surface is crucial for the selfaggregation of molecules via π-π stacking interactions, but also polarity, rigidity, and conformational flexibility of the molecules that govern the intermolecular association of gelators are important. Moreover, the incorporation of fluorophore (naphthalene) as an aromatic surface in the molecular designs enables the gelator molecules to execute the sensing of F- with a high degree of sensitivity in the solution phase.

The Ir-catalyzed asymmetric hydrogenation of cyclic pyridinium salts is presented as a new strategy for the convenient and efficient synthesis of chiral indolizidines. The asymmetric hydrogenation of cyclic pyridinium salts derived from 2-(2-acylphenyl)pyridines proceeded smoothly in the presence of [Ir(cod)Cl]2 and (R)-DM-SegPhos to provide the desired chiral 7,8-benzoindolizidines 6 in high to excellent yields with moderate enantioselectivity (up to 86:14 er) and excellent diastereoselectivity (>20:1 dr). The enantiomeric purity of 6j was increased to 92:8 through recrystallization.

A method for the synthesis of water-soluble α-aminopyrroles, 1-(2-amino-1H-pyrrol-3-yl)pyridinium chlorides, by the reaction 1-(cyanomethyl)pyridinium chloride with alkyl 3-aryl-2H-azirine-2-carboxylates was developed.

A library of trans-4,5-dihydrofuran-3-carbonitriles was synthesized in a diastereoselective manner in good yields by the three-component reaction of β-ketonitriles, carbonyl- and semistabilized pyridinium ylide precursors, and aldehydes in the presence of piperidine. This one-pot transformation generates two C-C and one C-O bond and proceeds through a cascade Knoevenagel condensation, a Michael addition, and intramolecular SN2 cyclization. Formation of cyclopropanecarbonitrile derivatives, which in some cases were obtained as major products, was found to be a competing reaction. The use of arylglyoxals changes regioselectivity and leads to 2-hydroxy-2H-pyran-5-carbonitriles.

Three-component condensation of in situ generated pyridinium acyl methylides with aromatic aldehydes and 4-hydroxythiocoumarin led to a series of 2-acyl-2,3-dihydro-4H-thiochromeno[4,3-b]furan-4-ones. The reaction proceeds diastereoselectively with the formation of trans-isomers and represents a cascade process involving the Knoevenagel condensation, carbo-Michael reaction, and intramolecular nucleophilic substitution. The subsequent redox rearrangement of 2-acyl-2,3-dihydro-4H-thiochromeno[4,3-b]furan-4-ones by the action of Zn and ZrCl4 grants access to 4H,5H-thiochromeno[4,3-b]pyran-5-ones.

A single-step approach is reported for the preparation of nitrones from benzyl halides and nitrosoarenes via pyridinium ylides, utilizing 4-dimethylaminopyridine (DMAP) catalyst and mild reaction conditions (Li2CO3, dimethylacetamide, and room temperature). The reaction provides both keto- and aldonitrones in high yields with a wide scope for benzyl halides and nitrosoarenes. In the same reaction system, 2-methyl-2-nitrosopropane, which does not have an aryl group, also affords the corresponding N-tert-butyl nitrones from primary benzyl bromides that have an electron-withdrawing group. As an application of the reaction, methyl 2-bromo-2-phenylacetate was used to prepare the corresponding isoxazolidine by a sequential one-pot synthesis.

Using the M06-2X method and IEFPCM for ethanol, geometries of various N-benzhydryl-X-pyridinium ions and corresponding heterolytic transition structures have been optimized to calculate free energies of activation (ΔG ‡model) for the model heterolysis of the ions at 25 °C. Very good correlations between ΔG ‡model values and corresponding measured ΔG ‡ values have made it possible to estimate reliable reactivities of N- (4, 4'-dimethoxybenzhydryl)-X-pyridinium ions in protic solvents as well as nucleofugality parameters (Nf calc) for 18 X-substituted pyridines. Computational results further reveal that geometric progression along the heterolytic reaction coordinate is synchronized with ionic charge transfer. A Leffler–Hammond coefficient of 0.65 (× 100%) corresponds to both the amount of the ionic charge transferred from the X-pyridine moiety to the alkyl electrofuge (65-67%) and the extent of geometric progression (64%) on proceeding from the ionic substrate to TS in the thermoneutral heterolysis. Consequently, exergonic heterolyses of very reactive N-alkyl-X-pyridinium ions proceed through the geometrically late transition states.

Pyridinium aldoximes are best-known therapeutic antidotes used for clinical treatment of poisonings by organophosphorus nerve-agents and pesticides. Recently, we found that pralidoxime (2-PAM, a currently clinically used nerve-agent antidote) could also detoxify tetrachloro-1,4-benzoquinone (TCBQ), which is a carcinogenic quinoid metabolite of the widely used wood preservative pentachlorophenol under normal physiological conditions, via an unusually mild and facile Beckmann fragmentation mechanism accompanied by radical homolysis. However, it is not clear whether the less-chlorinated benzoquinones (CnBQs, n ≤ 3) act similarly; if so, what is the structure-activity relationship? In this study, we found that (1) The stability of reaction intermediates produced by different CnBQs and 2-PAM was dependent not only on the position but also the degree of Cl-substitution on CnBQs, which can be divided into TCBQ- and DCBQ (dichloro-1,4-benzoquinone)-subgroup; (2) The pKa value of hydroxlated quinones (Cn-1BQ-OHs, the hydrolysis products of CnBQs), determined the stability of corresponding intermediates, that is, the decomposition rate of the intermediates depended on the acidity of Cn-1BQ-OHs; (3) The pKa value of the corresponding Cn-1BQ-OHs could also determine the reaction ratio of Beckmann fragmentation to radical homolysis in CnBQs/2-PAM. These new findings on the structure-activity relationship of the halogenated quinoid carcinogens detoxified by pyridinium aldoxime therapeutic agents via Beckmann fragmentation and radical homolysis reaction may have broad implications on future biomedical and environmental research.

A key step in gas-phase polycyclic aromatic hydrocarbon (PAH) formation involves the addition of acetylene (or other alkyne) to σ-type aromatic radicals, with successive additions yielding more complex PAHs. A similar process can happen for N-containing aromatics. In cold diffuse environments, such as the interstellar medium, rates of radical addition may be enhanced when the σ-type radical is charged. This paper investigates the gas-phase ion-molecule reactions of acetylene with nine aromatic distonic σ-type radical cations derived from pyridinium (Pyr), anilinium (Anl), and benzonitrilium (Bzn) ions. Three isomers are studied in each case (radical sites at the ortho, meta, and para positions). Using a room temperature ion trap, second-order rate coefficients, product branching ratios, and reaction efficiencies are measured. The rate coefficients increase from para to ortho positions. The second-order rate coefficients can be sorted into three groups: low, between 1 and 3 × 10-12 cm3 molecule-1 s-1 (3Anl and 4Anl); intermediate, between 5 and 15 × 10-12 cm3 molecule-1 s-1 (2Bzn, 3Bzn, and 4Bzn); and high, between 8 and 31 × 10-11 cm3 molecule-1 s-1 (2Anl, 2Pyr, 3Pyr, and 4Pyr); and 2Anl is the only radical cation with a rate coefficient distinctly different from its isomers. Quantum chemical calculations, using M06-2X-D3(0)/6-31++G(2df,p) geometries and DSD-PBEP86-NL/aug-cc-pVQZ energies, are deployed to rationalize reactivity trends based on the stability of prereactive complexes. The G3X-K method guides the assignment of product ions following adduct formation. The rate coefficient trend can be rationalized by a simple model based on the prereactive complex forward barrier height.

Two reaction modes of 1-sulfonyl-1,2,3-triazoles and pyridinium 1,4-zwitterionic thiolates were described. Pyrido[1,2-a]pyrazine derivatives were obtained in moderate yields when 4-OEt substituted triazoles were employed in reactions, and 1,4-thiazine derivatives were synthesized when 4-NPhth substituted triazoles were employed. The mechanism may involve a sulfur migration via an addition/elimination process which has never been reported in the previous pyridinium 1,4-zwitterionic thiolate related works.

A very simple and highly efficient protocol for synthesizing tetra- and penta-substituted benzene derivatives has been developed. This synthesis was achieved by carrying out a tetramethylguanidine (TMD)-promoted reaction of 4-(N,N-dimethylamino)-1-phenacyl-pyridinium bromide with chalcone o-enolates in DMF at 100 °C. The reaction mechanism was believed to involve a sequential annulation reaction of pyridinium ylide, ring-opening of the initially formed pyran ring and aromatization process.

A new stable pyridinium 1,5-zwitterion, generated from azadiene and 4-dimethylaminopyridine, was isolated for the first time. According to DFT calculations, the stability of this species was attributed to be the polarization effect on the exocyclic double bond. The reaction of pyridinium 1,5-zwitterion with isatin-derived α-(trifluoromethyl)imine was regulated by experimental temperature. The umpolung [4 + 3] annulation with isatin-derived α-(trifluoromethyl)imine was reported for the first time at 20 °C in CH3CN. In contrast, the formal Michael addition occurred when performing the reaction at reflux. Compared to the oxygen and methylene analogues, a sulfur atom changed the reaction mode from the umpolung [4 + 3] to the classical [3 + 2] annulation.

Zwitterionic compounds (ZIs) have been attracting much attention due to their properties. Unlike ionic liquids – constituted by separated ions – the ZI structures with their cations and anions covalently bonded exhibit added complexity and diversity, suggesting that their ecotoxicological behavior should probably not be extrapolated from those of ionic liquids. This study addresses the aquatic toxicity of ZIs towards the bacterium Allivibrio fischeri and the microalga Raphidocelis subcapitata. Sixteen ZIs comprising five different cationic groups (ammonium, imidazolium, pyridinium, pyrrolidinium and piperidinium) and two anionic groups (sulfonate and carboxylate) were studied, and the relationships between their structure and toxicity are reported. All studied ZIs are harmless or practically harmless for both microalga and bacterium (median effective concentration, EC50 >100 mg L−1), presenting a significantly lower hazardous potential to aquatic species than their ionic liquid counterparts. The results also show that the increased hydrophobicity of ZIs, owing to the increase of the cation alkyl chain or the spacer length, has a significant influence on EC50 values for microalga, which in turn causes higher toxicity. However, no significant differences were observed when considering the various cationic groups of the ZIs studied, unlike what is known for ecotoxicity of the ionic liquids. Also, no relationships were found between the chemical structure of ZIs and EC50 values determined for the bacterium A. fischeri. The structural differences between ZIs and ionic liquids result in different mechanisms of interactions with microalgae and bacteria membranes, which may explain why the ecotoxicity heuristic rules previously reported for ionic liquids do not seem to apply to ZIs. published

The discovery and optimization of a reaction between 2-chloropyridines and 2H-azirines producing imidazo[1,2-a]pyridines is described. The treatment of 2H-azirines with triflic anhydride (Tf2O) forms an electrophilic 1-trifloyl-aziridin-2-yl triflate species which, when reacted in situ with 2-halopyridines, generates transient pyridinium salts. These salts were treated in the same pot with triethylamine (Et3N), leading to the selective formation of C3-substituted imidazo[1,2-a]pyridines, an heterocyclic moiety commonly found in medicinal chemistry leads and drugs. Thorough optimization of the activation/cyclization resulted in yields ranging from 15 to 85% for a variety of substituted heterocycles.

The reactions of 2-pyridinesulfenyl halides with cyclopentene, 1,4-cyclohexadiene, 1,5-cyclooctadiene, 1,3-cyclooctadiene, and norbornene, depending on the structure of the alkene, the nature of the halogen, and the duration of the process, lead to the formation of two types of adducts, electrophilic addition products or condensed compounds, [1,3]thiazolo[3,2-a]pyridinium derivatives, in high yields.

C25H23Br2Cl3N2Sn, monoclinic, P21/c (no. 14), a = 10.9372(1) Å, b = 23.1045(1) Å, c = 11.1856(1) Å, β = 106.942(1)°, V = 2703.91(4) Å3, Z = 4, R gt (F) = 0.0167, wR ref(F 2) = 0.0393, T = 100 K.

Diazo-transfer reaction of tosyl azide and alkyl 2-cyanoacetates in the presence of pyridine at 0 °C gives the corresponding alkyl 2-cyano-2-diazoacetates. This material readily undergoes nucleophilic attack by pyridinium 1-cyano-2-alkoxy-2-oxoethan-1-ide to form dialkyl (Z)-3-amino-2-cyano-4-diazopent-2-enedioates. The X-ray structure of a typical product is reported, as well as DFT computational studies that illuminate the structural features of these stable diazo compounds.

Background: Our recent work has been treating the pharmacokinetics of pyridinium aldoximes of various structures including their time-dependent distribution in the body of male rats and also the extent of blood-brain-barrier penetration. Objective: Our overall aim was to find a proper antidote in organophosphate poisoning with fast elimination. Methods: White male Wistar rats were intramuscularly injected with the aqueous solution of 3 µmol of K-347. The animals were sacrificed at different time periods following treatment; various tissues and body fluids were taken and homogenised. The level of K-347 was determined using reversed-phase HPLC. Dose-dependence of tissue level was also determined by using various doses, 3 µmol through 100 µmol of K-347. Results: The serum level of K-347 showed a definitely fast decline. K347 did not have any effect on Gram-positive and Gram-negative bacteria that we tested. Conclusion: The kinetics of K-347 showed an extremely fast offset, even in comparison with several other pyridinium aldoximes in clinical practice and in developmental stages.

An enantioselective copper-catalyzed alkynylation of unstabilized cyclic iminium ions has been developed. Whereas such alkynylations typically utilize pyridinium, quinolinium, and isoquinolinium in...

The three-component condensation of pyridinium acylmethylides generated in situ with aromatic aldehydes and 4-hydroxy-6-methylpyridones gave a series of 2-acyl-3-aryl-3,5-dihydrofuro[3,2-c]pyridin-4(2H)-ones. The reaction proceeds diastereoselectively with the formation of trans-isomers and represents a cascade process involving the Knoevenagel condensation, the carbo-Michael reaction, and intramolecular nucleophilic substitution.

International audience; Novel 6-alkyl- and 6-alkenyl-3-fluoro-2-pyridinaldoximes have been synthesised by using a mild and efficient chemoselective hydrogenation of 6-alkynyl-3-fluoro-2-pyridinaldoxime scaffolds, without altering the reducible, unprotected, sensitive oxime functionality and the C-F bond. These novel 6-alkyl-3-fluoro-2-pyridinaldoximes may find medicinal application as antidotes to organophosphate poisoning. Indeed, one low-molecular-weight compound exhibited increased affinity for sarin-inhibited acetylcholinesterase (hAChE) and greater reactivation efficiency or resurrection for sarin-inhibited hAChE, compared with those of 2-pyridinaldoxime (2-PAM) and 1-({[4-(aminocarbonyl)pyridinio]methoxy}methyl)-2-[(hydroxyimino)methyl]pyridinium chloride (HI-6), two pyridinium salts currently used as antidote by several countries. In addition, the uncharged 3-fluorinated bifunctional hybrid showed increased in vitro blood-brain barrier permeability compared with those of 2-PAM, HI-6 and obidoxime. These promising features of novel low-molecular-weight alkylfluoropyridinaldoxime open up a new era for the design, synthesis and discovery of central non-quaternary broad spectrum reactivators for organophosphate-inhibited cholinesterases.

The first Pd/Cu catalyzed selective C2-alkenylation of pyridines with internal alkynes has been developed via the pyridinium salt activation strategy. Importantly, the configuration of the product alkenylpyridines could be tuned by the choice of the proper N-alkyl group of the pyridinium salts, thus allowing for both the Z- and E-alkenylpyridines synthesized with good regio- and stereoselectivity. A plausible mechanism was proposed based on the Hammett study and KIE experiment.

In this paper, we report the interaction of the cucurbit[7]uril (CB[7]) molecular container with bisstyryl dyes, (E)-1,1′-(propane-1,3-diyl)bis(4-(4-methoxystyryl)pyridinium) bromide (1) and (E)-1,1′-(propane-1,3-diyl)bis(4-(4-(dimethylamino)styryl)pyridinium) bromide (2), which differ from each other by presence of OCH3 (dye 1) or N(CH3)2 (dye 2) substituents in phenyl ring. The interaction of bisstyryl dyes with CB[7] results in the formation of different multicomponents complexes with composition (1)2@CB[7] and 1@(CB[7])2 and 2@CB[7] and 2@(CB[7])3. Complex formation was confirmed by a combination of optical, NMR and electrospray ionization mass spectroscopy (ESI-MS) methods. The composition of the formed complexes depends on the relative stoichiometry of dye and CB[7]. Complex formation is accompanied by substantial changes in the optical characteristics of the dyes and formation of excimer species.

Novel 2-amino-4-(nitromethylidene)chromenes were obtained as a result of the reaction of 1-(2-imino-2H-chromen-3-yl)pyridinium perchlorates and nitromethane by the action of DBU at reflux in trifluoroethanol. The starting 2-iminochromenes are readily accessible from the corresponding salicylic aldehydes and quaternary cyanomethyl pyridinium salts. The reaction is tolerant to substituents of different nature (alkyl, alkoxy, halogen); a limitation is the presence of strong electron-withdrawing substituents in the benzene ring of chromene. During the reaction, the products precipitate and can be isolated by filtration.

Les hétérocycles sont importants, aussi bien dans les domaines biologique, médicinal et thérapeutique (vitamines, hormones, antibiotiques, etc), que dans le secteur industriel et technologique (inhibiteurs de corrosion, colorants, agents stabilisants, pesticides, herbicides. Les chloroformiates ou chlorocarbonates sont les esters dérivés de l’acide chloroformique. La chimie des N-oxydes hétérocycliques (pyridine et N-oxydes) a connu un important développement au cours des dernières années. L’objectif principal du présent travail est l’étude de l’action du métoxycarbonylchloride sur la pyridine et certains de ses dérivés. Après avoir trouvé les conditions optimales, de nouveaux composés à base de pyridine ont été synthétisés. En remplaçant l’ion chlorure par d’autres ions, les produits synthétisés ont été cristallisés avec un bon rendement. La structure des produits a été caractérisée à l’aide de la spectroscopie infra rouge et la résonnance magnétique nucléaire. Spécifiquement, l’influence de la basicité du noyau hétérocyclique sur les enthalpies de formation des sels produits a été étudiée. En conclusion, la réaction chimique de formation est exothermique avec ΔH° < 0 pour tous les sels étudiés. En utilisant les constantes de Hammett sur le noyau de la pyridine, l’étude a monté que ces chaleurs de réaction dépendent de la basicité du noyau hétérocyclique. En perspective on peut envisager une étude de l’influence de la basicité des différents noyaux pyridiniques sur les effets de conjugaison polaire directe sur le groupe azoté dans les sels N-méthoxycarbonyl-(oxy)-pyridiniums.Mots clés: Pyridine N-Oxyde, chloroformiates, synthèse, constante de Hammett. English Title: Study of the influence of basicity on the enthalpy of reaction of N-methoxycarbonyl- (oxy) -pyridinium salts Heterocycles are important, as well in the biological, medicinal and therapeutic fields (vitamins, hormones, antibiotics, etc.), as in the industrial and technological sector (corrosion inhibitors, dyes, stabilizing agents, pesticides, herbicides). Chloroformates or chlorocarbonates are esters derived from chloroformic acid. The chemistry of heterocyclic N-oxides (pyridine and N-oxides) has experienced significant development in recent years. The main objective of this work is to study the action of metoxycarbonylchloride on pyridine and some of its derivatives. After finding the optimal conditions, new pyridine-based compounds were synthesized. By replacing the chloride ion with other ions, the synthesized products have been crystallized with good yield. Specifically, the influence of the basicity of the heterocyclic nucleus on the enthalpies of salt formation produced has been studied. The enthalpies formation of salt produced have been determined. In conclusion, the chemical reaction of formation is exothermic with ΔH ° < 0 for all the salts studied. Using Hammett's constants on the pyridine nucleus, the study has shown that these reaction heats depend on the basicity of the heterocyclic nucleus. In perspective, we can study the influence of the basicity of the different pyridine rings on the effects of direct polar conjugation on the nitrogen group in the N-methoxycarbonyl- (oxy) -pyridinium salts.Keywords: Pyridine N-Oxide, chloroformates, synthesis, Hammett constant.

A simple one-pot synthesis of N-substituted benzimidazoles from aromatic carboxylic acids and aromatic 1,2-diamines in the presence of 1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxide hexafluorophosphate/hydroxybenzotriazole (HATU/HOBT) and N,N-diisopropylethylamine in DMF at 100°C, featuring good to excellent yields and easy workup, is developed. The protocol can be scaled to gram quantities, and no chromatographic purification is required.

The crystal structures of two salt crystals of 2,2-bis­(4-methyl­phen­yl)hexa­fluoro­propane (Bmphfp) with amines, namely, dipyridinium 4,4′-(1,1,1,3,3,3-hexa­fluoro­propane-2,2-di­yl)dibenzoate 4,4′-(1,1,1,3,3,3-hexa­fluoro­propane-2,2-di­yl)di­benzoic acid (1) and a monohydrated ethyl­enedi­ammonium salt ethane-1,2-diaminium 4,4′-(1,1,1,3,3,3-hexa­fluoro­propane-2,2-di­yl)dibenzoate monohydrate (2) are reported., The crystal structures of two salt crystals of 2,2-bis­(4-methyl­phen­yl)hexa­fluoro­propane (Bmphfp) with amines, namely, dipyridinium 4,4′-(1,1,1,3,3,3-hexa­fluoro­propane-2,2-di­yl)dibenzoate 4,4′-(1,1,1,3,3,3-hexa­fluoro­propane-2,2-di­yl)di­benzoic acid, 2C5H6N+·C17H8F6O4 2−·C17H10F6O4, (1), and a monohydrated ethyl­enedi­ammonium salt ethane-1,2-diaminium 4,4′-(1,1,1,3,3,3-hexa­fluoro­propane-2,2-di­yl)dibenzoate monohydrate, C2H10N2 2+·C17H8F6O4 2−·H2O, (2), are reported. Compounds 1 and 2 crystallize, respectively, in space group P21/c with Z′ = 2 and in space group Pbca with Z′ = 1. The crystals of compound 1 contain neutral and anionic Bmphfp mol­ecules, and form a one-dimensional hydrogen-bonded chain motif. The crystals of compound 2 contain anionic Bmphfp mol­ecules, which form a complex three-dimensional hydrogen-bonded network with the ethyl­enedi­amine and water mol­ecules.

Cationic pyridinium pending chlorophyll-a derivatives with several counter anions were synthesized by Ag(I)-induced oxidation reactions of methyl pyropheophorbide-a possessing the 3-vinyl group wit...

4-[4-(2-Bromoacetyl)phenyl]-3-hydroxy-2H-chromen-2-one reacted with pyridine and 4-methylpyridine to give the corresponding quaternary pyridinium salts. The condensation of 1-{2-[4-(3-hydroxy-2-oxo-2H-chromen-4-yl)phenyl]-2-oxoethyl}-4-methylpyridinium bromide with 4-(dimethylamino)benzaldehyde afforded a new biscyanine dye whose electronic spectrum showed two absorption maxima originating from interactions of chromophores. The nature of electronic transitions in the dye molecule was analyzed by quantum chemical calculations.

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 alkyl and allyl groups were also successfully introduced via the same method. Additionally, the typically applied N-phenyl group in the THIQ substrate could be replaced by the cleavable p-methoxyphenyl (PMP) group and successful N-deprotection was demonstrated.

Herein, we report a radical borylation of aromatic amines through a homolytic C(sp2)−N bond cleavage. This method capitalizes on a simple and mild activation via a pyrylium reagent (ScPyry‐OTf) thus priming the amino group for reactivity. The combination of terpyridine and a diboron reagent triggers a radical reaction which cleaves the C(sp2)−N bond and forges a new C(sp2)−B bond. The unique non‐planar structure of the pyridinium intermediate, provides the necessary driving force for the aryl radical formation. The method permits borylation of a wide variety of aromatic amines indistinctively of the electronic environment., A radical borylation of aromatic amines through a homolytic C(sp2)−N bond cleavage is presented. This method capitalizes on a simple and mild activation via a pyrylium reagent (ScPyry‐OTf) that primes the amino group for reactivity. The combination of terpyridine and a diboron reagent triggers a radical reaction which cleaves the C(sp2)−N bond and forges a new C(sp2)−B bond. The non‐planar structure of the pyridinium, provides the necessary driving force for the challenging aryl radical formation.

New bispyridinium dichlorides based on 2,2-bis(hydroxymethyl)propane-1,3-diyl spacer were synthesized from pentaerythritol, 4-aminopyridine, and carboxylic acids. The resulting biocides possess a high antibacterial effect. The minimal inhibitory concentration (MIC) of these compounds against pathogenic bacteria, namely, gram-positive Methicillin-resistant Staphylococcus aureus (strain ATCC 25923) and gram-negative Escherichia coli (ATCC 25922) and Pseudomonas aeruginosa (ATCC 27853), was established. The influence of the alkyl substituent length in salts on their microbiological activity was studied.

Water-soluble 1-(3,5-di-tert-butyl-4-hydroxybenzyl)isatin 3-acylhydrazones containing an acyclic, bicyclic, or pyridinium quaternary ammonium center in the acyl moiety showed antibacterial activity against some gram-positive bacteria. Derivatives with a 2,3-dimethylpyridine or diazabicyclooctane fragment exhibited the highest activity against S. aureus and B. cereus as expressed by the minimum bactericidal concentration and were 4 times more active than chloramphenicol.

Polyfluoromethyl groups generally suffer from over-reaction, where multiple C–F bonds are uncontrollably functionalized. The use of a frustrated Lewis pair (FLP)-mediated C–F bond activation permits selective monodefluorination through base capture of intermediate fluorocarbocations. FLP-mediated C–F bond activation can be applied to aromatic, heteroaromatic, or nonaromatic difluoro and trifluoromethyl groups to generate selectively fluoride-substituted phosphonium and pyridinium salts. These salts can be further functionalized by Wittig coupling, nucleophilic substitution, photoredox alkylation, nucleophilic transfer, or hydrogenation reactions to install a range of functional groups into the activated C–F position.1 Introduction2 Frustrated Lewis Pair C–F Activation3 Conclusion

The nucleophilic addition of alkyl, benzyl, and allyl organozinc reagents to protected pyridinium riboses proceeds under mild conditions and with yields of >90% in several cases and complete regioselectivity for the 4-position.

Two new types of cyclic pyridinium ylides were designed and further used in reactions with azoalkenes to access structurally diverse spirocyclic compounds. A range of spiropyrazoline oxindoles could be smoothly obtained in up to 99% yield via a [4 + 1] annulation process with oxindole 3-pyridinium ylides as C1 synthons. Similarly, a series of spiropyrazoline indanones could be prepared with indanone 2-pyridinium ylides as C1 synthons. This work represents the first example of cyclic pyridinium ylides as C1 synthons for the efficient construction of spirocyclic compounds.

A highly efficient enantioselective dicarbofunctionalization reaction of (E)-alkenyloxindoles with pyridinium salts was realized. The process includes the chiral N,N′-dioxide–Sc(III) complex-catalyzed regio-, diastereo-, and enantioselective [3+2] cycloaddition reaction and the following photo-promoted aza-Norrish II type rearrangement. A series of 2-pyridyl substituted oxindole derivatives were obtained in good yields with moderate to good diastereo- and enantioselectivities.

A novel cyclization reaction of pyridinium 1,4-zwitterionic thiolates and propiolic acid derivatives mediated by triethylamine is described, which allows the facile synthesis of indolizines under mild reaction conditions. The net transformation involves an acetylide-driven formal [5 + 1] annulation reaction followed by a spontaneous ring-contraction/sulfur extrusion process of transient pyridothiazine intermediates.