Pyrylium Research Articles

Metal-Free Visible-Light-Promoted Trifluoromethylation of Vinylcyclopropanes Using Pyrylium Salt as a Photoredox Catalyst.

Visible-light-induced metal-free trifluoromethylation of activated, carbocyclic, and unactivated vinylcyclopropanes via a ring-opening reaction using the Langlois reagent (CF3SO2Na) is reported to synthesize allylic trifluoromethylated derivatives. Allylic trifluoromethylation was achieved by a photo-oxidative single electron transfer (SET) process at an ambient temperature and under metal-free conditions and visible-light irradiation using pyrylium salt as a photoredox catalyst. The reported methodology has an operational simplicity, broad substrate scope, high functional group tolerance, and scalability.

Visualization and Identification of Neurotransmitters in Crustacean Brain via Multifaceted Mass Spectrometric Approaches.

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) has emerged as a label-free analytical tool for fast biomolecule profiling on tissue sections. Among various functional molecules, mapping neurotransmitters and related metabolites is of tremendous significance, as these compounds are critical to signaling in the central nervous system. Here, we demonstrated the use of both derivatization and reaction-free approaches that greatly reduced signal complexity and thus enabled complementary signaling molecule visualization on crab brain sections via MALDI-LTQ-Orbitrap XL platform. Pyrylium salt served as a primary amine derivatization reagent and produced prominent signal enhancement of multiple neurotransmitters, including dopamine, serotonin, γ-aminobutyric acid, and histamine that were not detected in underivatized tissues. Molecules with other functional groups, such as acetylcholine and phosphocholine, were directly imaged after matrix application. The identities of discovered neurotransmitters were verified by standards using LC-MS/MS. This study broadens our understanding of metabolic signaling in the crustacean nervous system and highlights potential of multifaceted MS techniques for unambiguous neurotransmitter characterization.

Accelerated Chemical Synthesis: Three Ways of Performing the Katritzky Transamination Reaction

Typical laboratory exercises for undergraduate organic chemistry students involve bulk phase reactions with work up of product. In this study, students performed accelerated versions of the Katritzky reaction of para-substituted anilines with pyrylium salts in three ways: (i) by dropcasting reagents onto a paper surface and allowing solvent to evaporate, (ii) by evaporation of solvent from the reagent mixture in a rotary evaporator, and (iii) at an organic/water interface (“on water”). Students determined the reaction yield for all three accelerated reactions as well as in the conventional bulk phase by mass spectrometry. Acceleration factors (the ratio of the product to reagent ion signals in the accelerated vs conventional reaction) were used to compare the paper spray and rotary evaporator method as well as the “on water” method. Substituent effects were explored by using substituted anilines. Students’ understanding of acceleration of organic reactions was increased as seen in both laboratory reports and exit interviews.

Pyrylenes: A New Class of Tunable, Redox-Switchable, Photoexcitable Pyrylium-Carbene Hybrids with Three Stable Redox-States.

A new synthetic and modular access to a large family of redox-switchable molecules based upon the combination of pyrylium salts and carbenes is presented. The redox-properties of this new molecule class correlate very well with the π-accepting properties of the corresponding carbenes. While the pyrylium moiety acts as a chromophore, the carbene moiety can tune the redox-properties and stabilize the corresponding radicals. This leads to the isolation of the first monomeric pyranyl-radical in the solid-state. The three stable oxidation states could be cleanly accessed by chemical oxidation, characterized by NMR, EPR, UV-vis, and X-ray diffraction and supported by (TD)-DFT-calculations. The new hybrid class can be utilized as an electrochemically triggered switch and as a powerful photoexcited reductant. Importantly, the pyrylenes can be used as novel photocatalysts for the reductive activation of aryl halides and sulfonamides by consecutive visible light induced electron transfer processes.

Isobaric duplex based on a combination of 16O/18O enzymatic exchange and labeling with pyrylium salts

Enzymatic 18O exchange, the well-established approach in comparative proteomics, has some disadvantages such as back exchange of labeled oxygen and overlapping the peak of a labeled peptide with isotopic peaks of an unlabeled one. Herein we demonstrated a simple procedure in which samples digested with a trypsin (with and without H218O) were reacted with unlabeled and quadrupled 13C-labeled pyrylium salt respectively which results in formation of pyridinium cations. Thus, each isobarically labeled peptide containing zero or four 13C atoms in the mass reporter group, during tandem MS/MS forms an unique reporter ion useful for a relative quantitation. Such a sample treatment improves the signal to noise ratio, reduces overlapping of the isotopic peaks and completely eliminates the back exchange problem.

Concurrent mass spectrometric analysis of multiple samples using Py-Tag reagents

The quantification of amino acids, peptides and proteins are important in fundamental science to understand intravital event, as well as in applied fields such as biological, medical, and pharmaceutical sciences.Py-Tags (Py0, Py6 and Py12) are primary amine-reactive isotope-labelled tagging reagents. Py-Tags can selectively and efficiently react with the primary amino group which has more than a two-carbon chain from the alpha-carbon of the target sample by the reaction of pyrylium salts with nucleophiles under alkaline conditions, thereby increasing the mass by 175.15, 181.17, and 187.19 Da, respectively, and generating positive ions.We used Py-Tags to label not only the amino acids but also peptides with a lysine residue(s), fragment peptides with a lysine(s), digested proteins, and intact proteins. All Py-Tag-labelled peptide sets showed similar mass differences. Thus, we could easily analyze expression ratio by single measurement. Furthermore, the ratio of the measured ion intensities was representative of the relative amount of each material.

Optical and electronic properties of benzopyrylium derivatives. Theoretical-experimental synergy towards novel DSSCs devices

Here, we discuss the formation of several heterocyclic benzopyrylium compounds via joint experimental-theoretical efforts, in order to obtaining a better understanding of the diverse properties of these interesting organic species. Our results suggest these benzopyrylium dyes as interesting sensitizers in the novel design of new solar cells from the basis of their optical properties and pH-dependent characteristics. The role of aromatic stability of the pyrylium compounds in the obtained properties is discussed in terms of both NBO and analysis of the induced magnetic field toward the isotropic respond. Furthermore, optical properties were analyzed in the framework of TD-DFT methodologies. Noteworthy changes in red-shift and absorptions λmax are observed that contribute toward the interesting DSSCs applications. Additionally, the emission profile of 2a derivative was obtained in agreement to both theoretically and experimental strategy. We expect that our results can be informative for further development of heterocyclic benzopyrylium compounds and their application in DSSCs devices.

Accelerated reactions in field desorption mass spectrometry.

Field desorption mass spectrometry under ambient conditions is used to study solution-phase organic reactions in micro-volumes. Reagent solution is transferred onto the microdendrites of the field emitter, and reaction products are examined online by mass spectrometry. Three reactions, hydrazone formation by phenyl hydrazine and indoline-2,3-dione, the Katritzky reaction between a pyrylium salt and anisidine, and the Hantzsch synthesis of 1,4-dihydropyridine, were investigated, and reaction acceleration was observed to different extents. The increase in rate relative to the corresponding bulk reactions is attributed to solvent evaporation (simple concentration effect) and to the increase of surface-to-volume ratio (enhanced interfacial reactions). A distinguishing feature of this method of reaction acceleration, relative to that based on nano electrospray ionization, is the observation of radical cations and the formation of radical cation products. The study also breaks new ground in using field emitters at atmospheric pressure.

Selective Functionalization of Aminoheterocycles by a Pyrylium Salt.

The functionalization of aminoheterocycles by using a pyrylium tetrafluoroborate reagent (Pyry-BF4 ) is presented. This reagent efficiently condenses with a great variety of heterocyclic amines and primes the C-N bond for nucleophilic aromatic substitution. More than 60 examples for the formation of C-O, C-N, C-S, or C-SO2 R bonds are disclosed herein. In contrast to C-N activation through diazotization and polyalkylation, this method is characterized by its mild conditions and impressive functional-group tolerance. In addition to small-molecule derivatization, Pyry-BF4 allows the introduction of functional groups in a late-stage fashion to furnish highly functionalized structures.

Selective Functionalization of Aminoheterocycles by a Pyrylium Salt

AbstractThe functionalization of aminoheterocycles by using a pyrylium tetrafluoroborate reagent (Pyry‐BF4) is presented. This reagent efficiently condenses with a great variety of heterocyclic amines and primes the C−N bond for nucleophilic aromatic substitution. More than 60 examples for the formation of C−O, C−N, C−S, or C−SO2R bonds are disclosed herein. In contrast to C−N activation through diazotization and polyalkylation, this method is characterized by its mild conditions and impressive functional‐group tolerance. In addition to small‐molecule derivatization, Pyry‐BF4 allows the introduction of functional groups in a late‐stage fashion to furnish highly functionalized structures.

Supramolecular Kandinsky circles with high antibacterial activity

Nested concentric structures widely exist in nature and designed systems with circles, polygons, polyhedra, and spheres sharing the same center or axis. It still remains challenging to construct discrete nested architecture at (supra)molecular level. Herein, three generations (G2−G4) of giant nested supramolecules, or Kandinsky circles, have been designed and assembled with molecular weight 17,964, 27,713 and 38,352 Da, respectively. In the ligand preparation, consecutive condensation between precursors with primary amines and pyrylium salts is applied to modularize the synthesis. These discrete nested supramolecules are prone to assemble into tubular nanostructures through hierarchical self-assembly. Furthermore, nested supramolecules display high antimicrobial activity against Gram-positive pathogen methicillin-resistant Staphylococcus aureus (MRSA), and negligible toxicity to eukaryotic cells, while the corresponding ligands do not show potent antimicrobial activity.

Photoredox-Mediated Ring-Opening Metathesis Polymerization: Methods, Scope, and Scalability

Photoredox-mediated ring-opening metathesis polymerization (PhotoROMP) is a novel method for the preparation of ROMP polymers. As opposed to metal-mediated ROMP, which requires metal initiators, PhotoROMP utilizes organic photo-oxidants and vinyl ether initiators. In a recent study, a variety of pyrylium and thiopyrylium photo-oxidants were evaluated, demonstrating that milder photo-oxidants achieved higher conversions, and that thiopyrylium salts generally out-performed pyrylium salts. Further studies showed that polyolefins with polar functionality, such as protected alcohols and halides, can be prepared via PhotoROMP. This functionality could be leveraged for post-polymerization processing and functionalization. An evaluation of the stereochemistry of these polymers demonstrated that they are atactic, with roughly 75% trans olefin content. Ongoing work will probe the scalability of this reaction via flow chemistry. The polymer produced will be injection molded and the mechanical properties of PhotoROMP polymers and copolymers will be determined. Figure 1

Synthetic studies on a series of functionalized pyrylium salts, 4-chloro- and 4-bromophosphinines

A series of new pyrylium salts that bear sulfonate and phosphonate groups were obtained from the reactions between 2,6-diphenyl-4H-pyran-4-one, sulfonic anhydride, and chlorophosphates, and analyzed spectroscopically. Furthermore, treatment of 2,6-diphenyl-4H-pyran-4-one with phosphoryl chloride or bromide afforded the corresponding 4-chloro- and 4-bromopyrylium tetrafluoroborates in good yield. Subsequently, the synthesis of the corresponding 4-chloro- and 4-bromophosphinines was accomplished by treating the respective chloro- and bromopyrylium tetrafluoroborates with tris(trimethylsilyl)phosphine.

Some Considerations Regarding the 1H and 13C Spectra of 4-(1-azulenyl)-2,6-bis(2-heteroaryl-vinyl)- pyrylium and Pyridinium and their Corresponding Pyridines

The 1H and 13C NMR spectra of several 2,6-diheteroarylvinyl heterocycles containing 4-azulenyl moiety were recorded and their proton and carbon chemical shifts were compared with those of the compounds without double bond between the heterocycles. The influence of the nature of central and side heterocycles, molecule polarization and anisotropic effects were revealed. The highest chemical shifts were recorded for the pyrylium salts and the lowest at pyridines, but in the case of the pyridinium salts, the protons chemical shifts at the central heterocycle are more shielded due to a peculiar anisotropy of the attached vinyl groups.

Synthesis of a polymeric sensor containing an occluded pyrylium salt and its application in the colorimetric detection of trimethylamine vapors

ABSTRACTA dense membrane (MS) based on vinyl polymers and containing a pyrylium salt [2,6‐diphenyl‐4(p‐methacryloyloxy)phenylpyryliumtetrafluoroborate] was prepared. The MS has hydrophilic and sensory properties that make it a good material for the selective colorimetric detection of trimethylamine (TMA) vapors, a biogenic amine of great importance in food safety. The polymeric sensor changes from yellow to an intense pink color with increasing concentrations of TMA. The material could be reused in the presence of HCl vapors for at least 10 times. The detection and quantification limits were determined by ultraviolet–visible absorption spectroscopy (4.42 and 13.40 ppm, respectively) and by the RGB parameters of digital color (3.37 and10.22 ppm, respectively). © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46185.

Fingerprinting the Nature of Anions in Pyrylium Complexes: Dual Binding Mode for Anion-π Interactions.

The interplay between noncovalent interactions that involve oxygenated heteroaromatic rings have been studied for the first time in this work. In particular, we report an advance in knowledge-based anion-π interactions together with (C-H)+ ⋅⋅⋅anion contacts. To understand how the anion modulates these interactions, the synthesis of pyrylium salts with a variety of anions was performed by using an anionic metathesis methodology. The synthesized pyrylium complexes were classified in series, for example, anions derived from halogens, from oxoacids, from p-block elements, and from transition metals. Crystallographic data, DFT calculations, and NMR spectroscopy methods provided access to an overall insight into the noncovalent behavior of the anion in this kind of system. Based on the DFT calculations and 1 H NMR spectroscopy, pyrylium protons can be used as chemical tags to detect noncovalent interactions in this type of compound.

Photoorganocatalysis, small organic molecules and light in the service of organic synthesis: the awakening of a sleeping giant.

Photocatalysis, the use of light to promote organic transformations, is a field of catalysis that has received limited attention despite existing for over 100 years. With the revolution of photoredox catalysis in 2008, the rebirth or awakening of the field of photoorganocatalysis has brought new ideas and reactions to organic synthesis. This review will focus on the sudden outburst of literature regarding the use of small organic molecules as photocatalysts after 2013. In particular, it will focus on acridinium salts, benzophenones, pyrylium salts, thioxanthone derivatives, phenylglyoxylic acid, BODIPYs, flavin derivatives, and classes of organic molecules as catalysts for the photocatalytic generation of C-C and C-X bonds.

Electron paramagnetic resonance spectroscopic studies of the electron transfer reaction of Hantzsch ester and a pyrylium salt.

The oxidation of Hantzsch ester by a pyrylium cation takes place via electron–proton–electron transfer. The reaction was investigated with EPR spectroscopy using TEMPO and DMPO for inhibition and spin trapping, respectively, of the radicals appearing during the reaction. The present in-depth EPR study of the radical reactions of a NADH analogue indicate a complex electron transfer mechanism in the title reaction.

Substituent effects in pyridyl-functionalized pyrylium salts, pyridines and λ3,σ2-phosphinines: a fundamental and systematic study.

A series of substituted, pyridyl-functionalized 2,4,6-triarylpyrylium salts were prepared and investigated for their light absorption and emission properties. After reaction with P(SiMe3)3, the corresponding λ3-phosphinines were obtained, which carry on the 4- or 6-aryl ring ±I and ±M substituents. Supported by DFT calculations, a systematic evaluation of the σ-donor and π-donor as well as π-acceptor properties of these low-coordinate P,N-hybrid ligands was performed. The modular synthetic approach allowed us at the same time to synthesize the structurally related bipyridine derivatives for comparison reasons. Reaction of the chelating ligands with [W(CO)6] in THF afforded the corresponding [(P^N)W(CO)4] and [(N^N)W(CO)4] complexes. A crystallographic characterization of selected coordination compounds revealed significant structural differences between the pyridyl-phosphinine- and the bipyridine-based compounds. Their characterization by means of IR-spectroscopy gave experimental insight into the electronic properties of the respective ligands.

Полиметиновые красители на основе пирилиевых солей, содержащих в четвертом положении ненасыщенные циклические группировки

Полиметиновые красители на основе пирилиевых солей, содержащих в четвертом положении ненасыщенные циклические группировки