Azinium Salts Research Articles

Nucleophilic trifluoromethylation of azinium salts with Zn(CF3)2·bpy

(Trifluoromethyl)zinc complexes have been widely used in metal-mediated trifluoromethylation reactions. However, direct nucleophilic addition with a (trifluoromethyl)zinc complex is rare. In this article, we describe an unprecedented trifluoromethylation of azinium salts using Zn(CF3)2·bpy as CF3 source, giving 1-(4-methoxybenzyl)-2-(trifluoromethyl)-1,2-dihydroquinolines as products. The latter species were further transformed to 2-trifluoromethylquinolines under oxidative conditions. This work also shows that ligands play an important role in tuning the reactivity of (trifluoromethyl)zinc complexes.

Azine Steric Hindrances Switch Halogen Bonding to N-Arylation upon Interplay with σ-Hole Donating Haloarenenitriles.

An interplay between 4-bromo- and 4-iodo-5-nitrophthalonitriles (XNPN, X=Br or I) and any one of the azines (pyridine 1, 4-dimethylaminopyridine 2, isoquinoline 3, 4-cyanopyridine 4, 2-methylpyridine 5, 2-aminopyridine 6, quinoline 7, 1-methylisoquinoline 8, and 2,2'-bipyridine 9) proceeds differently depending on steric and electronic effects of the heterocycles. Sterically unhindered azines 1-3 underwent N-arylation to give the corresponding azinium salts (characterized by 1 H and 13 C{H} NMR and high-resolution ESI-MS). In contrast, azines 4-9 with sterically hindered N atoms or bearing an electron-withdrawing substituent, form stable co-crystals with XNPN, where two interacting molecules are bound by halogen bonding. In all obtained co-crystals, X⋅⋅⋅N structure-directed halogen bonds were recognized and theoretically evaluated including DFT calculations (PBE0-D3/def2-TZVP level of theory), QTAIM analysis, molecular electrostatic potential surfaces, and noncovalent interaction plot index. Estimated energies of halogen bonding vary from -7.6 kcal/mol (for 6 ⋅ INPN) to -11.4 kcal/mol (5 ⋅ INPN).

Cyclative MCRs of Azines and Azinium Salts

Since the first discovery by Huigsen and co‐workers fifty years ago, a wide range of organic reactions have taken place through the intermediary of the dipolar/zwitterionic species produced by the combination of a neutral nucleophile and an unsaturated electrophile. Nucleophilic initiators including heterocycles may react or play a mediating role based on their nucleophilic nature and reaction conditions. This review highlights the recent developments of the cyclization chemistry of heterocycles using multicomponent reactions (MCRs) – including unusual dearomatizative examples. Heterocycles as very common structural units can often be found in natural and pharmaceutical products. MCRs are environmentally benign and highly atom economic reactions. Their application in the synthesis of biologically active molecules may provide alternatives for the greener synthesis of drugs lowering the carbon footprint of pharmaceutical industries.

Nucleophilic Dearomatization of Pyridines under Enamine Catalysis: Regio-, Diastereo-, and Enantioselective Addition of Aldehydes to Activated N-Alkylpyridinium Salts.

Catalytic addition of chiral enamines to azinium salts is a powerful tool for the synthesis of enantioenriched heterocycles. An unprecedented asymmetric dearomative addition of aldehydes to activated N-alkylpyridinium salts is presented. The process exhibits complete C-4 regioselectivity along with high levels of diastereo- and enantiocontrol, achieving a high-yielding synthesis of a broad range of optically active 1,4-dihydropyridines. Moreover, the presented methodology enables the synthesis of functionalized octahydropyrrolo[2,3-c]pyridines, the core structure of anticancer peptidomimetics.

Spectroscopic investigation of interactions of new potential anticancer drugs with DNA and non-ionic micelles.

Photophysical properties of some azinium iodides in aqueous solution of nanostructured systems as DNA and nonionic micelles were investigated using steady-state and ultrafast time-resolved spectroscopy. Spectrophotometric and fluorimetric titrations of the investigated compounds with salmon testes DNA supplied evidence of a good interaction between the salts and DNA with binding constants of 10(4)-10(6) M(-1), making them interesting for pharmaceutical applications. The interaction with DNA also changes the photobehavior of the compounds, increasing the radiative deactivation pathway to the detriment of internal conversion and slowing down the excited state dynamics. The interaction of the azinium salts with the nonionic surfactant Triton X-100 from premicellar to postmicellar concentration was studied by spectrophotometric and fluorimetric titrations evidencing the ability of the micelles to associate the studied salts in their hydrophobic portion and to release them in the presence of DNA, acting as promising drug carriers. Also transient absorption spectroscopy with femtosecond resolution demonstrated the insertion of the investigated compounds into micellar aggregates. Preliminary measurements by confocal fluorescence microscopy on MCF-7 cells in the presence of the studied azinium salts showed that they are able to cross the cellular membrane and that their cytotoxicity can be expressed through interaction with DNA (RNA). In fact, they showed a significant fluorescence signal in all cell compartments, particularly (for 2 and 3) into punctuate structures within the nuclei compatible with a localization into the nucleoli.

Photobehaviour of methyl-pyridinium and quinolinium iodide derivatives, free and complexed with DNA. A case of bisintercalation.

Excited state dynamics of four azinium salts were studied in buffered water and in the presence of salmon testes DNA. Complexation with DNA changes the photobehaviour of the free ligands lowering the photoreactivity and emission in favor of internal conversion. The interaction of these four dyes with DNA was studied with different techniques with the aim to establish the affinity and the type of binding between the ligands and DNA. The results from spectrophotometric and fluorimetric titrations provided evidence of a strong interaction between the azinium salts and the polynucleotide, with a binding constant of about 10(6) M(-1), making them interesting for therapeutical applications. Dichroic measurements allowed us to determine the possible modes of binding for each complex. Short living excited states of the free dyes were detected and characterized by ultrafast absorption spectroscopy. A further decrease of transient lifetimes was observed upon interaction with DNA. The bicationic pyridinium iodide was found to act as a bisintercalative agent, potentially increasing the cytotoxicity with low dose and less collateral effects.

ChemInform Abstract: Ring‐Closing Metathesis Reactions on Azinium Salts: Straightforward Access to Quinolizinium Cations and Their Dihydro Derivatives.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Ring-Closing Metathesis Reactions on Azinium Salts: Straightforward Access to Quinolizinium Cations and Their Dihydro Derivatives

The ring-closing metathesis reaction of 1-butenyl-2-vinylpyridinium salts and 2-butenyl-1-vinylpyridinium salts using Grubbs second generation and Hoveyda-Grubbs catalysts proved to be an efficient approach to 3,4-dihydro- and 1,2-dihydroquinolizinium salts and the corresponding quinolizinium derivatives by an improved thermal oxidation in the presence of Pd/C without solvent. A comparative study showed that the quinolizinium system was obtained in better yields through the 3,4-dihydroquinolizinium route, thus allowing the synthesis of quinolizinium derivatives or improvements in the yields of some examples reported previously.

A New Approach to Polycyclic Azonia Cations by Ring-Closing Metathesis

The ring-closing metathesis (RCM) reaction of N-vinyl-alpha-(2-styryl)azinium salts, using the Hoveyda-Grubbs catalyst, leads to different tricyclic and tetracyclic azonia cations with moderate to good yields. This is the first time that a highly electron-deficient alkene such as an N-vinylpyridinium has been involved in an RCM process.

Synthesis of Perfluoroalkyl-Substituted Azines via Nucleophilic Substitution of Hydrogen with Perfluoroisopropyl Carbanions

Perfluoroisopropyl carbanions generated in situ by treatment of perfluoropropene (HFP) with solid KF in the appropriate solvents add to N-alkylpyridinium, quinolinium, and other azinium salts to give reasonably stable N-alkyldihydroazines containing a perfluoroisopropyl group. In most cases, addition proceeds in position 2 of the heterocyclic ring. Stability of these dihydroazines depends on the nature of the N-alkyl group and other substituents present in the azine ring. The least stable of them were converted into their stable C-trifluoroacetyl derivatives in reaction with trifluoroacetic anhydride. Treatment of N-benzyl- or N-p-methoxybenzyl-2-perfluoroisopropyl dihydroazines with oxidizing agents such as DDQ or cerium(IV) ammonium nitrate results in cleavage of the benzylic C-N bond followed by oxidation of the ring, giving pyridines or quinolines with a perfluoroisopropyl group in the aromatic ring. On the basis of these findings, a new protocol for introduction of perfluoroalkyl substituents into azine rings was elaborated via oxidative nucleophilic substitution of hydrogen. It involves three chemical steps: (i) alkylation of azine with p-MeOC6H4CH2Br, (ii) reaction of the resulting salt with fluorinated carbanions generated in situ from HFP and KF, and (iii) N-deprotection and aromatization of the isolated dihydroazine on treatment with CAN. The first two reactions, (i) and (ii), can be performed as a one-pot operation.

From a three-component synthesis to multistep cascade reactions. Twenty years of chemistry of N-(1-haloalkyl)azinium halides

N-(1-Haloalkyl)azinium halides are readily available through a three-component reaction of an azine, an aldehyde, and a thionyl halide. Those salts represent activated forms of the starting aldehydes and can be used advantageously for the preparation of other azinium salts, imines, 1,1diamines, and a wide range of nitrogen (fused) heterocycles. Recently it has also been demonstrated that N-(1-haloalkyl)azinium halides can be transformed into bis(1,3,4-thiadiazolo)1,3,5-triazinium halides, a novel class of versatile tricyclic systems that exhibits many useful synthetic potentialities.

Cyclotransformation of Azinium Salts into Hydrogenated Cyclic Alkylamino Ketones.

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Cyclotransformation of Azinium Salts into Hydrogenated Cyclic Alkylamino Ketones

A study was carried out on the nucleophilic cyclotransformation of pyrrolo[1,2-a]pyrazinium salts and isoquinolinium salts containing a methyl group in the α-position. A method for the preparation of alkylaminotetrahydroindolizinones and tetralones was proposed.

4-(4-Chloro-phenyl)-pyrimidinium ylides. 1. Structure, stability, reactivity

In this paper we present a theoretical and experimental study concerning the structure, stability, and reactivity of 4-(4-chlorophenyl)pyrimidinium ylides. 4-(4-Chlorophenyl)-pyrimidinium ylides are relatively stable compounds, their stability varying with the nature of the ylide carbanion substituent. The stronger the electron-withdrawing effect of these substituents, the more the anionic charge is delocalized, and therefore the higher their stability. The experimental and quantum chemical calculations confirm this hypothesis and are in accordance with each other. The electronic absorption spectra of 4-(4-chlorophenyl)-pyrimidinium 4-X-benzoyl methylides can be assigned to an intramolecular charge transfer band. The quantum chemical calculations show the possibility to use pyrimidinium ylides as nucleophilic reagents as well as 1,3-dipoles in reaction with appropriate reagents. The influence of microwave irradiation for the synthesis of azinium salts was also studied. The reaction of 4-(4-chlorophenyl)pyrimidine with an organic haloalkane shows a remarkable rate acceleration under microwave irradiation and allows a general and facile synthesis of azinium salts. A comparative study of microwave and classical conditions (use of solvents) has been done.

A Unified Approach to Quinolizinium Cations and Related Systems by Ring-Closing Metathesis

[reaction: see text] The first example of an olefin ring-closing metathesis reaction on cationic heteroaromatic systems is described. Dihydroquinolizinium cations and a variety of related cationic systems are synthesized in an efficient approach from N-alkenyl alpha-vinyl azinium salts using Grubbs' catalysts.

1-Aza-2-azoniaallene salts: reactions with azomethines and other N-nucleophiles

Azomethines undergo nucleophilic addition to 1-aza-2-azoniaallene salts 7 to furnish N-(azoalkyl)iminium salts (e.g. 10, 12, 13). With cyclic hydrazones such as pyrazole or indazole, heterocumulenes 7 afford bicyclic 1,2,4,5-tetrazinium salts (e.g. 14, 16), or simple N-adducts such as 15, 17. On the other hand, with open-chain hydrazones azinium salts 19 are formed. Benzotriazole and the aziridine 21 react with 1-aza-2-azoniaallene salts 7 to afford (azoalkyl)ammonium salts 20, 22. The heterocumulenes 7 undergo cycloaddition across the CN double bond of the azirine 23 to furnish azirenotriazolium salts 25, while with the 1-aza-2-azoniaallene salt 3a the triazolium salt 28 was formed. The constitutions of compounds 22, 25a and 28 were confirmed by X-ray structural analyses.

Azole additions upon azinium salts

The additions of pyrrole and indole upon N-acetyl- and N-alkylpyridinium, quinolinium or isoquinolinium salts are reported. The resulting dihydroazines are either isolated or oxidised to the more stable aromatic compounds. The use of a two-phase system was studied and slight enantiomeric excesses were observed when chiral catalysts were used. The separation of enantiomers of some 4-indolyl-1,4-dihydropyridines was achieved by HPLC using chiral stationary phases.

3+3]-Cyclocondensation of aminomethylenecycloalkanones with cyclic azomethines — A new approach to condensed nitrogen heterocycles

A new method was developed for the synthesis of condensed azinium salts with a nitrogen atom in the ring fusion based on the [3+3]-cyclocondensation of aminomethylenecycloalkanones and cyclic azomethines.

Synthesis of Polyfused Heteroaromatics by Palladium–Catalyzed Cross–Coupling Reaction

The palladium-catalyzed coupling of unsaturated halides or triflates with organostannanes (the Stille reaction) or with organo-boronic acids (the Suzuki reaction) has envolved as a powerful means of carbon-carbon bond formation. As an extention of our work on the synthesis and reactivity of positively charged bridge-head nitrogen containing fused azinium salts, we have been studying the formation of polyfused heteroaromatics with angular anellation pattern.The reaction of such positively charged salts with nucleophiles has proven to be a suitable tool for the preparation of heteroaryl dienes, which have been shown to be excellent intermediates for several ring closure reaction. A selection of results will be presented, including applications to natural product synthesis.

ChemInform Abstract: Synthesis, Isomerization and Chemical Transformation of Phenacyl Oxime Azinium Salts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.