Chichibabin “isodesmopyridine” synthesis

2,3,5-Trisubstituted pyridine isodesmopyridine is one of the elastin crosslinking amino acid which was isolated from the acid hydrolysates of bovine ligamentum nuchae. Biosynthesis of isodesmopyridine is believed to undergo via Chichibabin pyridine synthesis starting from aldehydes and an ammonia. Herein, we report the first total synthesis of isodesmopyridine through Chichibabin pyridine synthesis from allysines with protecting groups and ammonium salts in the presence of 50?mol% Pr(OTf)₃ with the optimization of the reaction conditions.     

Knoevenagel‐Michael‐cyclocondensation Tandem Reaction of Malononitrile,Various Aldehydes and Dimedone Catalyzed by Sulfonic Acid Functionalized Pyridinium Chloride as a New Ionic Liquid and Catalyst

New ionic liquid sulfonic acid functionalized pyridinium chloride [Pyridine–SO₃H]Cl was used for the synthesis of tetrahydrobenzo[b]pyran derivatives by the one‐pot three component condensation reaction of various aldehydes, dimedone and malononitrile at 95 ºC under solvent‐free conditions.     

Pr(OTf)3-promoted Chichibabin pyridine synthesis of isodesmosine in H2O/MeOH

1,2,3,5-Tetrasubstituted pyridinium amino acid isodesmosine is a crosslinking amino acid of elastin and is an attractive biomarker for the diagnosis of chronic obstructive pulmonary disease (COPD). Herein, we report an application of the Chichibabin pyridine synthesis to the total synthesis of isodesmosine. Specifically, the appropriate protected lysine and the corresponding aldehyde were reacted using Pr(OTf)₃ in H₂O/MeOH.     

Particular behavior of ‘C6C2 units’ in the Chichibabin pyridine synthesis and biosynthetic implications

Several aspects of the unusual behavior of C₆C₂ aldehydes and amines during the formation of pyridiniums in analogy with the historical Chichibabin pyridine synthesis are clarified in this Letter. Interesting biosynthetic consequences are also discussed within two classes of polycyclic alkaloids of marine origin.     

Synthesis of C3-dihydrofuran substituted coumarins via multicomponent approach

An efficient method was developed for the synthesis of dihydrofuran substituted coumarin from a one-pot, four-component reaction of 2-hydroxy aromatic aldehydes, 6-methyl, 4-hydroxy pyranone, aromatic aldehyde, and pyridinium ylide in the presence of tri-ethylamine under microwave irradiation. The reaction proceeds under solvent-free conditions to afford C3-dihydrofuran substituted coumarin in a diastereoselective manner in good yields (71–89%).     

Iodine‐Promoted Synthesis of 1‐Alkyl‐3‐aroylindolizines from N‐(Aroylmethyl)pyridinium Salts and Aliphatic Aldehydes

An effective and practical method has been developed for the diversity‐oriented synthesis of 1‐alkyl‐3‐aroylindolizines via the 1,3‐dipolar cycloaddition of pyridinium ylides and aliphatic aldehydes in the presence of molecular iodine and a catalytic amount of MnO₂. The synthesis proceeds by tandem reactions involving [3+2] cycloaddition, dehydration of the cycloadduct, and dehydroaromatization. Molecular iodine served both as a catalyst and a dehydroaromatization reagent in the reaction.     

Columnar bis(pyridinium) ionic liquid crystals derived from 4-hydroxypyridine: synthesis,mesomorphism and emission properties

A series of flexibly linked bis(pyridinium) salts with various counterions (Br^?, PF₆^?, BF₄^? and OTf-) was designed and prepared starting from corresponding N-alkylated 4-pyridones precursors with mesogenic 3,4,5-tris(alkyloxy)benzyl moieties (alkyl = dodecyl or tetradecyl). These salts were investigated for their liquid crystalline properties by a combination of differential scanning calorimetry, polarising optical microscopy and temperature-dependent powder X-ray diffraction (XRD). Their thermal stability was checked by thermogravimetric analysis. All bis(pyridinium) salts, except the triflate salt with shorter terminal carbon chain, display an enantiotropic liquid crystalline behaviour with a hexagonal columnar (Col_h) phase assigned on the basis of its characteristic texture and XRD studies. It was found that these luminescent bis(pyridinium) salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. The emission properties of these bis(pyridinium) salts do not depend significantly on the nature of counterion employed.     

Novel pyridinium salts as cationic thermal and photoinitiators and their photosensitization properties

Novel pyridinium salts [N‐(α‐phenylbenzyl)‐, N‐(1‐naphthylmethyl)‐, or N‐cinnamyl p‐ or o‐cyanopyridinium hexafluoroantimonates] were synthesized by the reaction of p‐ or o‐cyanopyridine and the corresponding bromides followed by anion exchange with KSbF₆. These pyridinium salts polymerized epoxy monomers at lower temperatures than previously reported for N‐benzyl‐2‐cyanopyridinium hexafluoroantimonate. The o‐substituted pyridinium salts showed higher activity than the p‐substituted ones, and the crosslinked epoxy polymers cured with these initiators showed higher glass‐transition temperatures. These pyridinium salts photoinitiated radical polymerization as well as cationic polymerization. The photopolymerization was accelerated by the addition of aromatic ketones as photosensitizers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1037–1046, 2002     

γ-Trimethylsilyl(triphenylsilyl) pyridines in syntheses of silicon-containing pyridinium ylids and indolizines

Three N-phenacyl--trimethylsilyl (triphenylsilyl)pyridinium bromides were converted to stable silyl-substituted pyridinium ylids. Six previously unknown silicon-containing indolizines were obtained by two methods, viz., 1,3-dipolar cycloaddition of dimethyl acetylenedicarboxylate (DMAD) to the pyridinium ylids and the Chichibabin reaction. Spectral data that confirm the structures of the synthesized compounds are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 965–968, July, 1980.     

RhIII‐Catalyzed C?H Activation: A Versatile Route towards Various Polycyclic Pyridinium Salts

An efficient and convenient method for the synthesis of highly substituted polycyclic pyridinium salts from the reaction of various 2‐aryl‐pyridines and 2‐aryl‐sp²‐nitrogen‐atom‐containing heterocycles with alkynes through rhodium(III)‐catalyzed C? H activation and annulation under an O₂ atmosphere is described. A possible mechanism that involves the chelation‐assisted C? H activation of the 2‐aryl‐pyridine substrate, insertion of the alkyne, and reductive elimination is proposed. This mechanism was supported by the isolation of a five‐membered rhodacycle ( I′ ). In addition, kinetic isotope studies were performed to understand the intimate reaction mechanism.     

Facile and Green Synthesis of 1,4-Dihydropyridine Derivatives in n-Butyl Pyridinium Tetrafluoroborate

l,4-Dihydropyridine derivatives were synthesized from the one-pot condensation of aldehydes, acetoacetates, and ammonium acetate in room-temperature ionic liquid n-butyl pyridinium tetrafluoroborate ([BPy][BF₄]). Compared with classical Hantzsch reaction conditions, this new method has the advantage of excellent yields, short reaction time, and easy workup. The recovered ionic liquid could be recycled for at least five runs without losing its activity.     

Intramolecular Pyridinium Oxide Cycloadditions: Systematic Study of Substitution,Diastereoselectivity, and Regioselectivity

Intramolecular pyridinium oxide cycloadditions form complex polycyclic nitrogenous architectures. The diastereoselectivity and regioselectivity of pyridinium oxide cycloadditions was systematically investigated for the first time using complex substrates. Predictably high levels of diastereoselectivity and regioselectivity are observed, which can be attributed to minimization of steric (syn-pentane) and torsional strain in the products. The reaction is reversible under the reaction conditions, and it is stereospecific with respect to the dipolarophile geometry.     

Sulfonic acid pyridinium chloride-functionalized nanoparticles (MnCoFe2O4@Niacin-SO3H)+Cl− as a novel and reusable catalyst for synthesis of tetrahydrodipyrazolopyridines and pyranopyrazoles

The novel pyridinium chloride-functionalized MnCoFe₂O₄-SO₃H nanoparticles, (MnCoFe₂O₄@Niacin-SO₃H)⁺Cl^?, were synthesized by coating the sulfonic group on the surface of MnCoFe₂O₄@Niacin. The activity of these nanoparticles was studied for the synthesis of tetrahydrodipyrazolopyridines and pyranopyrazole derivatives via the multi-component reactions of ethyl acetate, hydrazine, aldehydes, and ammonium acetate or malononitrile. The use of green solvent, easy separation of the catalyst from the reaction medium, easy deposition, high purity, and openness of products are some advantages of this procedure.

     

Nucleophilic Functionalization of 2-Alkylidene-4-Oxothiazolidines at C(5)-Position Induced by Formation of Novel Pyridinium Salt

Abstract

The synthesis of unsubstituted pyridinium salt containing the 4-oxothiazolidine moiety bondedviaC(5) to the N position of the pyridine nucleus is reported. The nucleophilic displacement of pyridine from pyridinium salt by the selected nucleophiles leads to the formation of new 5-substituted 4-oxothiazolidines in good yields.     

A new variant of the synthesis ofβ,γ′-bipyridyl by means of the Chichibabin reaction

A new method for the synthesis ofβ,γ′-bipyridyl by the Chichibabin reaction has been carried out.     

Molecular structures of 3‐[(2,2,3,3‐tetrafluoropropoxy)methyl]‐ and 3‐[(2,2,3,3,3‐pentafluoropropoxy)methyl]pyridinium saccharinates

The salts 3‐[(2,2,3,3‐tetrafluoropropoxy)methyl]pyridinium saccharinate, C₉H₁₀F₄NO⁺·C₇H₄NO₃S⁻, (1), and 3‐[(2,2,3,3,3‐pentafluoropropoxy)methyl]pyridinium saccharinate, C₉H₉F₅NO⁺·C₇H₄NO₃S⁻, (2), i.e. saccharinate (or 1,1‐dioxo‐1λ⁶,2‐benzothiazol‐3‐olate) salts of pyridinium with –CH₂OCH₂CF₂CF₂H and –CH₂OCH₂CF₂CF₃meta substituents, respectively, were investigated crystallographically in order to compare their fluorine‐related weak interactions in the solid state. Both salts demonstrate a stable synthon formed by the pyridinium cation and the saccharinate anion, in which a seven‐membered ring reveals a double hydrogen‐bonding pattern. The twist between the pyridinium plane and the saccharinate plane in (2) is 21.26 (8)° and that in (1) is 8.03 (6)°. Both salts also show stacks of alternating cation–anion π‐interactions. The layer distances, calculated from the centroid of the saccharinate plane to the neighbouring pyridinium planes, above and below, are 3.406 (2) and 3.517 (2) Å in (1), and 3.409 (3) and 3.458 (3) Å in (2).     

Orientational ordering of pyridinium ion in its tetrabromoaurate(III) salt

Heat capacity and dielectric measurements of crystalline pyridinium tetrabromoaurate(III), (pyH)AuBr₄, were carried out in the temperature ranges of 13 to 300 K and 30 to 160 K, respectively. A phase transition, due to the orientational ordering of pyridinium ions, was found at 99.9 K. A glass transition, due to freezing-in of the reorientational motion of pyridinium ions, was found at around 60 K. An anomaly showing the intermediate situation between Schottky effect and phase transition was found with the heat-capacity peak at around 260 K. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Economic Synthesis of Pyridinium Fluorochromate(VI), C5H5NH[CrO3F] (PFC), and Solvent‐Free Oxidation of Organic Substrates with PFC

Abstract

A 1:1:1 stoichiometric reaction among CrO₃, aqueous HF and pyridine affords orange crystalline pyridinium fluorochromate(VI), C₅H₅NH[CrO₃F] (PFC), in 99.2% isolated yield. The reagent under solvent‐free conditions readily converts benzylic, secondary, and allylic alcohols to the corresponding carbonyls and selectively oxidizes secondary alcohols in the presence of primary alcohols, polycyclic hydrocarbons to cyclic ketones, benzoin to benzil, PPh₃ to O?PPh₃, methylphenyl sulfide to sulfoxide, cyclohexanone oxime to cyclohexanone, an allylic Δ⁵‐steroid to the corresponding α,β‐unsaturated ketone and deprotects dioxolanes and dithiolanes to aldehydes; the economic synthesis of PFC, its ease of reaction without solvent, versatility, and high isolated yields of the products are the significant features of the protocol.     

Design of anhydrous electrorheological (ER) suspensions based on I2-doped poly(pyridinium salt)

A rigid-rod aromatic poly(pyridinium salt) was synthesized and doped with iodine (I₂) for making anhydrous electrorheological (ER) fluids. The I₂-doped particles were further processed into ones having insulating skins. Dielectric properties and current densities of the suspensions containing these particles were studied to elucidate the roles of conductivity of the dispersed phase in the ER suspension. © 1994 John Wiley & Sons, Inc.