- On the Electron-Donating Properties of Oxygen vs. Sulfur. Redox Potentials for Some Pyrylium and Thiapyrylium Salts
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The redox levels for two series of pyrylium and thiapyrylium salts were measured by cyclic voltammetry.This information was utilized to provide a quantitative comparison of the highest occupied (HOMO) and lowest unoccupied molecular orbitals (LUMO) which is a measure of the thermodynamic stabilities to electron transfer of oxygen vs. sulfur adjacent to carbon cation, radical, and anionic centers in a single system.In one of the series dicationic, cationic, radical, and anionic centers were compared.The ionic and radical species were found to be thermodynamically more stable in the sulfur analogue (less stable in oxygen analogue) in every case except when the HOMO and/or LUMO level is localized on the diethylaminophenyl moiety.The order of the greatest sulfur preference or least oxygen preference is the following: anion>radical and radical>cation for the HOMO and LOMO levels, respectively.The wavelength of the intramolecular charge transfer band and the electrochemical reduction potentials indicate that the thiapyrylium moiety is more electron withdrawing than pyrylium.
- Saeva, F. D.,Olin, G. R.
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- Radical alkylation of isocyanides with amino acid-/peptide-derived Katritzky salts via photoredox catalysis
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An efficient and mild method was developed for the synthesis of 6-alkylated phenanthridines upon visible light irradiation. Bench-stable and easily handled redox-active Katritzky pyridinium salts derived from abundant amino acids/peptides were used as radical precursors for the alkylation of isocyanobiphenyl species. The reaction displays an excellent functional group tolerance and a potential utility for peptide functionalization, allowing access to desired products in good to excellent yields.
- Zhu, Ze-Fan,Zhang, Miao-Miao,Liu, Feng
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- 4-Benchrotrenyl pyrylium salts as protein organometallic labelling reagents
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Pyrylium ions are useful reagents to selectively modify the amino group of protein lysine residues. This property was exploited here to label proteins with chromium tricarbonyl complexes in the form of 4-benchrotrenyl pyridinium ions. Kinetic studies of the reaction of a series of benchrotrenyl pyrylium salts with water and n-butylamine were performed and revealed that the overall reactivity of these compounds was highly dependent on their substitution pattern. These compounds could find application in protein X-ray crystallography.
- Caro, Bertrand,Le Guen-Robin, Fran?oise,Salmain, Michèle,Jaouen, Gérard
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- Dissection of alkylpyridinium structures to understand deamination reactions
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Via conversion to Katritzky pyridinium salts, alkyl amines can now be used as alkyl radical precursors for a range of deaminative functionalization reactions. The key step of all of these methods is single-electron reduction of the pyridinium ring, which triggers C-N bond cleavage. However, little has been done to understand how the precise nature of the pyridinium influences these events. Using a combination of synthesis, computation, and electrochemistry, this study delineates the steric and electronic effects that substituents have on the canonical steps and the overall process. Depending on the approach taken, consideration of both the reduction and the subsequent radical dissociation may be necessary. Whereas the electronic effects on these steps work in opposition to each other, the steric effects are synergistic, with larger substituents favoring both steps. This understanding provides a framework for future design of pyridinium salts to match the mode of catalysis or activation.
- Tcyrulnikov, Sergei,Cai, Qiuqi,Cameron Twitty,Xu, Jianyu,Atifi, Abderrahman,Bercher, Olivia P,Yap, Glenn P. A.,Rosenthal, Joel,Watson, Mary P.,Kozlowski, Marisa C.
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- Ruthenium-catalysedmeta-selective CAr-H bond alkylationviaa deaminative strategy
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The use of aliphatic amines as alkylating reagents in organic synthesisviaC-N bond activation remains underdeveloped. We herein describe a novel ruthenium-catalysed and directing-group assisted protocol for the synthesis ofmeta-alkylated arenesviadual C-H and C-N activation. Bench-stable and easily handled redox-active Katritzky pyridinium salts derived from abundant amines and amino acid species were used as alkyl radical precursors. This catalytic reaction could accommodate a broad range of functional groups and provide access to variousmeta-alkylated products.
- Zhu, Ze-Fan,Chen, Guang-Le,Liu, Feng
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supporting information
p. 3411 - 3414
(2021/04/07)
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- Continuous-Flow Synthesis of Pyrylium Tetrafluoroborates: Application to Synthesis of Katritzky Salts and Photoinduced Cationic RAFT Polymerization
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Katritzky salts have emerged as effective alkyl radical sources upon metal- or photocatalysis. These are typically prepared from the corresponding triarylpyrylium ions, in turn an important class of photocatalysts for small molecules synthesis and photopolymerization. Here, a flow method for the rapid synthesis of both pyrylium and Katrizky salts in a telescoped fashion is reported. Moreover, several pyrylium salts were tested in the photoinduced RAFT polymerization of vinyl ethers under flow and batch conditions.
- Sambiagio, Carlo,Ferrari, Matteo,Van Beurden, Koen,Ca', Nicola Della,Van Schijndel, Jack,Noel, Timothy
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supporting information
p. 2042 - 2047
(2021/04/05)
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- Synthesis method of 2, 4, 6-triphenylpyran tetrafluoroborate
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The invention discloses a synthesis method of 2, 4, 6-triphenylpyran tetrafluoroborate, and relates to the technical field of photoelectric materials. The synthesis method comprises the following steps that benzaldehyde and acetophenone are mixed and stirred, the reaction temperature is controlled to range from 15 DEG C to 25 DEG C, boron trifluoride diethyl etherate is dropwise added into a reaction system, the temperature is increased to 50 DEG C to 80 DEG C after dropwise adding is completed, a reaction is conducted for 15 h, when the reaction liquid is cooled to 40 DEG C, the reaction liquid is injected into ethyl acetate under stirring, a yellow solid is separated out, and filtered and purified so as to obtain 2, 4, 6-triphenylpyran tetrafluoroborate; the molar ratio of benzaldehyde to acetophenone is 1: 3, and the mass ratio of boron trifluoride diethyl etherate to acetophenone is 9: 11. The method has the beneficial effects that the 2, 4, 6-triphenylpyran tetrafluoroborate is synthesized by adopting a one-pot method, the synthesis method is simple, the product yield is high, the purity is high, and the industrialization of the product is easy to realize.
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Paragraph 0019-0033
(2021/06/22)
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- C-H Alkylation of Aldehydes by Merging TBADT Hydrogen Atom Transfer with Nickel Catalysis
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Catalyst controlled site-selective C-H functionalization is a challenging but powerful tool in organic synthesis. Polarity-matched and sterically controlled hydrogen atom transfer (HAT) provides an excellent opportunity for site-selective functionalization. As such, the dual Ni/photoredox system was successfully employed to generate acyl radicals from aldehydes via selective formyl C-H activation and subsequently cross-coupled to generate ketones, a ubiquitous structural motif present in the vast majority of natural and bioactive molecules. However, only a handful of examples that are constrained to the use of aryl halides are developed. Given the wide availability of amines, we developed a cross-coupling reaction via C-N bond cleavage using the economic nickel and TBADT catalyst for the first time. A range of alkyl and aryl aldehydes were cross-coupled with benzylic and allylic pyridinium salts to afford ketones with a broad spectrum of functional group tolerance. High regioselectivity toward formyl C-H bonds even in the presence of α-methylene carbonyl or α-amino/oxy methylene was obtained.
- Murugesan, Vetrivelan,Ganguly, Anirban,Karthika, Ardra,Rasappan, Ramesh
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supporting information
p. 5389 - 5393
(2021/07/21)
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- Photocatalytic deaminative benzylation and alkylation of tetrahydroisoquinolines with N-alkylpyrydinium salts
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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.
- No?l, Timothy,Sambiagio, Carlo,Sch?nbauer, David,Schnürch, Michael
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supporting information
p. 809 - 817
(2020/05/18)
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- Nickel-Catalyzed Cross-Coupling of Alkyl Carboxylic Acid Derivatives with Pyridinium Salts via C-N Bond Cleavage
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The electrophile-electrophile cross-coupling of carboxylic acid derivatives and alkylpyridinium salts via C-N bond cleavage is developed. The method is distinguished by its simplicity and steers us through a variety of functionalized ketones in good to excellent yields. Besides acid chlorides, carboxylic acids were also employed as acylating agents, which enabled us to incorporate acid-sensitive functional groups such as MOM, BOC, and acetal. Control experiments with TEMPO revealed a radical pathway.
- Pulikottil, Feba Thomas,Pilli, Ramadevi,Suku, Rohith Valavil,Rasappan, Ramesh
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supporting information
p. 2902 - 2907
(2020/04/09)
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- Ni-Catalyzed deaminative hydroalkylation of internal alkynes
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A regioselective cis-hydroalkylation of internal alkynes with readily prepared Katritzky pyridinium salts for the synthesis of tri-substituted alkenes is described. This reaction is the first example of a metal-catalyzed hydroalkylation of an alkyne via C-N bond activation of an amine. The reaction demonstrates broad scope and functional group tolerance, allowing access to desired products with high diversity. Preliminary mechanistic studies indicate that a combination of an SET-initiated radical process and Ni-catalyzed alkylation could engage in the reaction, which makes it possible to bypass the traditional open-shell addition pathway.
- Liu, Feng,Tu, Jia-Lin,Zhu, Ze-Fan
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supporting information
p. 11478 - 11481
(2019/09/30)
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- A PROCESS FOR THE PREPARATION OF PYRYLIUM SALTS
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The present invention relates to the process for the preparation of Pyrylium salts having the formula represented below. Present invention provide a simplified method of producing symmetrical and unsymmetrical pyrylium salts. The invention explores readily available starting materials with reaction conditions which are suitable for industrial scale applications. All the synthesized compounds were confirmed by various spectroscopic techniques such as Fourier transform infrared spectroscopy, 1H NMR, 13C NMR, 19F NMR spectroscopy, and single-crystal X-ray analysis. Mass of the compounds confirmed by HRMS analysis.
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Page/Page column 6; 7
(2019/08/29)
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- Visible-light mediated trifluoromethylation of p-quinone methides by 1,6-conjugate addition using pyrylium salt as organic photocatalyst
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A transition metal free visible light mediated organo photoredox catalyzed trifluoromethylation of p-quinone methides (p-QMs) to construct fluoro-analogs of dichlorodiphenyltrichloroethane (DDT) is reported using a bench stable, inexpensive Langlois reagent as a trifluoromethyl radical source. This protocol could generate a benzylic C(sp3)-CF3 bond with excellent yield under mild reaction conditions using 1,6-conjugate addition/aromatization of trifluoromethyl radical in the absence of any external additives. Further, we demonstrate di-trifluoromethylation and gram scale synthesis of this reaction.
- Ghosh, Krishna Gopal,Chandu, Palasetty,Mondal, Santanu,Sureshkumar, Devarajulu
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p. 4471 - 4478
(2019/07/09)
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- Visible-light-induced oxidation/[3 + 2] cycloaddition/oxidative aromatization to construct benzo[ a]carbazoles from 1,2,3,4-tetrahydronaphthalene and arylhydrazine hydrochlorides
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An efficient synthesis of benzo[a]carbazoles via visible-light-induced tandem oxidation/[3 + 2] cycloaddition/oxidative aromatization reactions was reported. The benzylic C(sp3)-H of tetrahydronaphthalene was activated through visible-light photoredox catalyst with oxygen as the clean oxidant under mild reaction conditions. This protocol proceeds efficiently with broad substrate scope, and the mechanism study was performed.
- Shen, Jiaxuan,Li, Nannan,Yu, Yanjiang,Ma, Chunhua
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supporting information
p. 7179 - 7183
(2019/09/30)
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- Topotactic Synthesis of Phosphabenzene-Functionalized Porous Organic Polymers: Efficient Ligands in CO2 Conversion
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Progress toward the preparation of porous organic polymers (POPs) with task-specific functionalities has been exceedingly slow—especially where polymers containing low-oxidation phosphorus in the structure are concerned. A two-step topotactic pathway for the preparation of phosphabenzene-based POPs (Phos-POPs) under metal-free conditions is reported, without the use of unstable phosphorus-based monomers. The synthetic route allows additional functionalities to be introduced into the porous polymer framework with ease. As an example, partially fluorinated Phos-POPs (F-Phos-POPs) were obtained with a surface area of up to 591 m2 g?1. After coordination with Ru species, a Ru/F-Phos-POPs catalyst exhibited high catalytic efficiency in the formylation of amines (turnover frequency up to 204 h?1) using a CO2/H2 mixture, in comparison with the non-fluorinated analogue (43 h?1) and a Au/TiO2 heterogeneous catalysts reported previously (?1). This work describes a practical method for synthesis of porous organic phosphorus-based polymers with applications in transition-metal-based heterogeneous catalysis.
- Yang, Zhenzhen,Chen, Hao,Li, Bo,Guo, Wei,Jie, Kecheng,Sun, Yifan,Jiang, De-en,Popovs, Ilja,Dai, Sheng
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supporting information
p. 13763 - 13767
(2019/08/21)
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- Synthesis of symmetrical and unsymmetrical triarylpyrylium ions: Via an inverse electron demand Diels-Alder reaction
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BF3·OEt2 mediated inverse electron demand Diels-Alder (IEDDA) reaction of chalcones with aryl acetylenes is reported for the synthesis of symmetrical and unsymmetrical 2,4,6-triarylpyrylium ions. The protocol provides an effective one-pot method for the utilization of readily available simple substrates under mild reaction conditions leading to a diverse array of pyrylium ions in moderately good yield.
- Fathimath Salfeena,Basavaraja,Ashitha,Kumar, V. Praveen,Varughese, Sunil,Suresh, Cherumuttathu H.,Sasidhar
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p. 12463 - 12466
(2018/11/20)
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- Characterization of amine stabilized CdSe/ZnS core-shell quantum dots by using triarylpyrylium dyes
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A new method to study the stabilizing primary amine ligands coordinated to the surface of CdSe/ZnS core-shell quantum dots has been developed. The method is based on the reactivity of fluorescent 2,4,6-triarylpyrylium dyes with the aforementioned ligands to afford non-emissive 2,4,6-triarylpyridinium cations.
- Beltrán, Alicia,Burguete, M. Isabel,Luis, Santiago V.,Galindo, Francisco
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p. 56064 - 56068
(2016/07/06)
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- Electronically tunable anion-π interactions in pyrylium complexes: Experimental and theoretical studies
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Noncovalent interactions of anions with electron-deficient aromatic rings that have been studied so far involve non-heteroaromatic or nitrogen-based heteroaromatic systems. Here we report the first case of an organic oxygenated aromatic system, in particular the tri-aryl-pyrylium tetrafluoroborate system, for which noncovalent anion-π interactions of the pyrylium cation with the tetrafluoroborate anion have been experimentally detected and demonstrated by means of 19F NMR spectroscopy in solution. A series of pyrylium tetrafluoroborate salts were synthesized in the presence of BF 3·Et2O, by direct reaction of 4-substituted benzaldehydes with 4-substituted acetophenones or via the previously obtained chalcone of the less reactive ketone. Correlations of 19F NMR chemical shifts of tetrafluoroborate anion for most of the synthesized tri-arylpyrylium tetrafluoroborate complexes with both the pyrylium cation molecular weight and the standard substituent Hammett constants, demonstrate anion-π+ interaction to act between the polyatomic anion BF 4- and the pyrylium aromatic system. DFT calculations reveal that an additional (C-H)+-anion hydrogen bond involving the H(5) of pyrylium ring exists for these fluorescent dyes that show a tunable cup-to-cap shape cavity. The strong fluorescence emission observed for some representative pyrylium tetrafluoroborates described herein, makes them a promising class of tunable emission wavelength dyes for laser technology applications. the Partner Organisations 2014.
- Franconetti, Antonio,Contreras-Bernal, Lidia,Jatunov, Sorel,Gomez-Guillen, Manuel,Angulo, Manuel,Prado-Gotor, Rafael,Cabrera-Escribano, Francisca
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p. 18442 - 18453
(2014/10/15)
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- Cyclization-endoperoxidation cascade reactions of dienes mediated by a pyrylium photoredox catalyst
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Triarylpyrylium salts were employed as single electron photooxidants to catalyze a cyclization-endoperoxidation cascade of dienes. The transformation is presumed to proceed via the intermediacy of diene cation radicals. The nature of the diene component was investigated in this context to determine the structural requirements necessary for successful reactivity. Several unique endoperoxide structures were synthesized in yields up to 79%.
- Gesmundo, Nathan J.,Nicewicz, David A.
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supporting information
p. 1272 - 1281
(2014/06/24)
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- A rapid approach toward synthesis of 1,3,5-triarylpent-2-ene-1,5-diones catalyzed by KF/Al2O3 and PEG-400 using microwave irradiation
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A rapid and efficient method for the synthesis of 1,3,5-triarylpent-2-ene- 1,5-diones is described based on a low-cost and environmentally benign KF/Al2O3 and PEG-400 co-catalyst catalyst via open-ring reactions of 2,4,6- triarylpyrylium salts compounds under microwave irradiation conditions. The advantage of this method is satisfactory yields, short reaction time and the use of a cheaper, milder, and efficient catalyst. Finally, twelve α, β-unsaturated diones have been obtained in good to excellent yields by this procedure.
- Song, Mingzhi,Fan, Chuangang
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- Cyclometalation of aryl-substituted phosphinines through C-H-bond activation: A mechanistic investigation
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A series of 2,4,6-triarylphosphinines were prepared and investigated in the base-assisted cyclometalation reaction using [Cp*IrCl2] 2 (Cp=1,2,3,4,5-pentamethylcyclopentadienyl) as the metal precursor. Insight in the mechanism of the C-H bond activation of phosphinines as well as in the regioselectivity of the reaction was obtained by time-dependent 31P{1H}NMR spectroscopy. At room temperature, 2,4,6-triarylphosphinines instantaneously open the Ir-dimer and coordinate in an η1-fashion to the metal center. Upon heating, a dissociation step towards free ligand and an Ir-acetate species is observed and proven to be a first-order reaction with an activation energy of ΔE A=56.6kJ mol-1 found for 2,4,6-triphenylphosphinine. Electron-donating substituents on the ortho-phenyl groups of the phosphorus heterocycle facilitate the subsequent cyclometalation reaction, indicating an electrophilic C-H activation mechanism. The cyclometalation reaction turned out to be very sensitive to steric effects as even small substituents can have a large effect on the regioselectivity of the reaction. The cyclometalated products were characterized by means of NMR spectroscopy and in several cases by single-crystal X-ray diffraction. Based on the observed trends during the mechanistic investigation, a concerted base-assisted metalation-deprotonation (CMD) mechanism, which is electrophilic in nature, is proposed. Finely tuned: A series of substituted 2,4,6-triarylphosphinines were prepared and investigated in a base-assisted cyclometalation reaction using [Cp*IrCl 2]2 (Cp=1,2,3,4,5-pentamethylcyclopentadienyl) as the metal precursor M (see figure). Insight into the mechanism of the C-H bond activation of phosphinines as well as into the regioselectivity of the reaction was obtained by using time-dependent 31P{1H}NMR spectroscopy and single-crystal X-ray diffraction. Copyright
- Broeckx, Leen E. E.,Güven, Sabriye,Heutz, Frank J. L.,Lutz, Martin,Vogt, Dieter,Müller, Christian
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p. 13087 - 13098
(2013/10/01)
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- Single-step versus stepwise two-electron reduction of polyarylpyridiniums: Insights from the steric switching of redox potential compression
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Contrary to 4,4′-dipyridinium (i.e., archetypal methyl viologen), which is reduced by two single-electron transfers (stepwise reduction), the 4,1′-dipyridinium isomer (so-called "head-to-tail" isomer) undergoes two electron transfers at apparently the same potential (single-step reduction). A combined theoretical and experimental study has been undertaken to establish that the latter electrochemical behavior, also observed for other polyarylpyridinium electrophores, is due to potential compression originating in a large structural rearrangement. Three series of branched expanded pyridiniums (EPs) were prepared: N-aryl-2,4,6-triphenylpyridiniums (Ar-TP), N-aryl-2,3,4,5,6-pentaphenylpyridiniums (Ar-XP), and N-aryl-3,5-dimethyl-2,4,6- triphenylpyridinium (Ar-DMTP). The intramolecular steric strain was tuned via N-pyridinio aryl group (Ar) phenyl (Ph), 4-pyridyl (Py), and 4-pyridylium (qPy) and their bulky 3,5-dimethyl counterparts, xylyl (Xy), lutidyl (Lu), and lutidylium (qLu), respectively. Ferrocenyl subunits as internal redox references were covalently appended to representative electrophores in order to count the electrons involved in EP-centered reduction processes. Depending on the steric constraint around the N-pyridinio site, the two-electron reduction is single-step (Ar = Ph, Py, qPy) or stepwise (Ar = Xy, Lu, qLu). This steric switching of the potential compression is accurately accounted for by ab initio modeling (Density Functional Theory, DFT) that proposes a mechanism for pyramidalization of the Npyridinio atom coupled with reduction. When the hybridization change of this atom is hindered (Ar = Xy, Lu, qLu), the first reduction is a one-electron process. Theory also reveals that the single-step two-electron reduction involves couples of redox isomers (electromers) displaying both the axial geometry of native EPs and the pyramidalized geometry of doubly reduced EPs. This picture is confirmed by a combined UV-vis-NIR spectroelectrochemical and time-dependent DFT study: comparison of in situ spectroelectrochemical data with the calculated electronic transitions makes it possible to both evidence the distortion and identify the predicted electromers, which play decisive roles in the electron-transfer mechanism. Last, this mechanism is further supported by in-depth analysis of the electronic structures of electrophores in their various reduction states (including electromeric forms).
- Fortage, Jerome,Peltier, Cyril,Perruchot, Christian,Takemoto, Yohei,Teki, Yoshio,Bedioui, Fethi,Marvaud, Valerie,Dupeyre, Gregory,Pospisil, Lubomir,Adamo, Carlo,Hromadova, Magdalena,Ciofini, Ilaria,Laine, Philippe P.
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supporting information; experimental part
p. 2691 - 2705
(2012/03/22)
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- Designing multifunctional expanded pyridiniums: Properties of branched and fused head-to-tail bipyridiniums
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The multifaceted potentialities of expanded pyridiniums (EPs), based on one pyridinium core bearing a 4-pyridyl or 4-pyridylium as the N-pyridinio group, are established at both experimental and theoretical levels. Two classes of head-to-tail (htt) EPs were designed, and their first representative elements were synthesized and fully characterized. The branched (B) family is made up of 2,6-diphenyl-4-aryl-1,4′-bipyridin-1-ium (or 1,1′-diium) species, denoted 1B and 2B for monocationic EPs (with aryl = phenyl and biphenyl, respectively) and 1BMe and 2BMe for related quaternarized dicationic species. The series of fused (F) analogues comprises 9-aryl-benzo[c]benzo[1,2]quinolizino[3,4,5,6-ija][1,6]naphthyridin-15-ium species, denoted 1F and 2F, and their 2,15-diium derivatives referred to as 1FMe and 2FMe. Electrochemistry (in MeCN vs SCE) reveals that branched EPs undergo a single reversible bielectronic reduction at ca. -0.92 V for 1B/2B and -0.59 V for 1BMe/2BMe, whereas pericondensed species show two reversible monoelectronic reductions at ca. -0.83 and -1.59 V for 1F/2F and ca. -0.42 and -1.07 V for 1FMe/2F Me. Regarding electronic absorption features, all htt-EP chromophores show absorptivity in the range of ca. 1-4 × 104 M-1 cm-1, with red-edge absorptions extending toward 450 and 500 nm (in MeCN) for 2BMe and 2FMe, respectively. These lowest-energy pi-pi* transitions are ascribed to intramolecular charge transfer between the electron-releasing biphenyl group and the htt-bipyridinium electron-withdrawing subsystems. EPs display room-temperature photoemission quantum yields ranging from 10% to 50%, with the exception of 1B, and branched luminophores are characterized by larger Stokes shifts (8000-10 000 cm -1) than fused ones. Lastly, a method to predict the efficiency of photobiscyclization of branched EPs into fused ones, based on the analysis of computed difference maps in total electron density for singlet excited states, is proposed.
- Fortage, Jerome,Peltier, Cyril,Nastasi, Francesco,Puntoriero, Fausto,Tuyeras, Fabien,Griveau, Sophie,Bedioui, Fethi,Adamo, Carlo,Ciofini, Ilaria,Campagna, Sebastiano,Laine, Philippe P.
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supporting information; experimental part
p. 16700 - 16713
(2011/02/23)
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- A convenient regioselective synthesis of 2,4-diarylfurans
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A facile three step process, under mild conditions, for the synthesis of 2,4-diarylfurans with the same or different substituents on the two aryl rings, starting from benzaldehydes and acetophenones, employing Haller-Bauer type cleavage of 2-aroyl-3,5-diarylfurans is described.
- Francesconi, Iris,Patel, Alpa,Boykin, David W.
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- A concise preparation of η3-allylpalladium tetrafluoroborates from N-allylpyridinium tetrafluoroborates [1]
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N-allyl-2,4,6-triphenylpyridinium tetratluoroborates react with bis(dibenzylideneacetone) palladium(0) and two equivalents of triphenylphosphine, or one equivalent of diphosphine, to give η3-allyl palladium tetrafluoroborates, 2,4,6-triphenylpyridine acting as neutral leaving group. Springer-Verlag Iberica 1996.
- Malet, Ramon,Moreno-Manas, Marcial,Pleixats, Roser
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- Direct Photolysis and Electron Transfer Photooxygenation of Enol Acetates of 3-Phenylpropiophenones
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Direct photolysis of enol acetates of 3-phenylpropiophenones 1a-c gives rise to the parent propiophenones 2a-c and the 1,3-acyl shift products 3a-c.By contrast, 2,4,6-triphenylpyrylium tetrafluoroborate sensitized photolysis of substrates 1a-c affords the α-acetyloxypropiophenones 7a-c as the most general products.These results have been rationalized according to the generation of radical pairs in the direct photolysis and radical cations in the photoinduced electron transfer processes. Keywords.Enol acetates of 3-phenylpropiophenones; 1,3-Acyl migration; Photoinduced electron transfer; 2,4,6-triphenylpyrylium tetrafluoroborate.
- Algarra, Felipe,Baldovi, Maria V.,Garcia, Hermenegildo,Miranda, Miguel A.,Primo, Jaime
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p. 209 - 216
(2007/10/02)
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- Electron Transfer Photofragmentations of 3-Phenylpropiophenones
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Photolysis of 3-phenylpropiophenones 1 a-d in the presence of 2,4,6-triphenylpyrylium tetrafluoroborate (TPT) yields the corresponding α,β-unsaturated ketones 2 a-c and 1 d (from 1c), together with acetophenone (3), benzophenone (4), benzoic acid (5) and benzaldehyde (6), presumably by fragmentations of the radical cation 1+*, generated via a single electron transfer process from 1 to the excited TPT.
- Baldovi, Maria V.,Garcia, Hermenegildo,Miranda, Miguel A.,Primo, Jaime
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p. 371 - 375
(2007/10/02)
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- REACTIONS OF ACETOPHENONES AND BORON TRIFLUORIDE ETHERATE IN THE PRESENCE OF HOMOLOGS OF ORTHOFORMIC ESTER
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It was established that homologs of orthoformic ester (orthoacetic and orthopropionic esters), in contrast to it, do not undergo reaction with substituted acetophenones and boron trifluoride etherate to give γ-alkylpyrylium salts; the products obtained are 2,4,6-triarylpyrylium tetrafluoroborates.
- Boiko, I. I.,Dergunova, M. E.,Boiko, T. N.
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p. 1169 - 1171
(2007/10/02)
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- Electrochemical Reactions. Part 26. Radicals Derived by Reduction of N-Alkylpyridinium Salts and Homologous N,N'-Polymethylenebispyridinium Salts. Cleavage of the Carbon-Nitrogen Bond
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The stability of the radical zwitterions derived by electron addition to N-alkyl-2,4,6-triphenyl- and 4-phenylpyridinium salts has been examined.Rapid carbon-nitrogen bond cleavage occurs for benzyl and allyl substituents only when the 2,6-diphenyl substituents are present.The N-propyl group is not lost.Homologous N,N'-polymethylenebis(2,4,6-triphenylpyridinium) salts show two reversible one electron waves, distinct for the ethylene derivative and merging as the carbon chain lengthens so that ΔEo reaches the theoretical value of (RT/F) ln 4.
- Grimshaw, James,Moore, Shirley,Trocha-Grimshaw, Jadwiga
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p. 485 - 490
(2007/10/02)
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- Kinetics and Mechanisms of Nucleophilic Displacements with Heterocycles as Leaving Groups. Part 4. 2,4,6-Triaryl-N-benzylpyridinium Cations: Rate Variation with Electronic Effects in the Leaving Group
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Electron-withdrawing groups in the 4-phenyl ring of 2,4,6-triphenylpyridine modestly increase its activity as a leaving group.Replacement of 2-phenyl by heteroaryl has a small effect for monoheteroaryl groups, but significantly larger for 2-benzimidazol-2-yl and especially for 2-benzothiazol-1-yl.
- Katritzky, Alan R.,Adamson, Jeffrey,Elisseou, E. Michael,Musumarra, Giuseppe,Patel, Ranjan C.,et al.
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p. 1041 - 1048
(2007/10/02)
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- Boron Trifluoride as a Cyclodehydrating Agent: Synthesis of Nitrogen Heterocycles via Pyrylium Tetrafluoroborates
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Pyrylium cations (1-12,Z = O+) have been prepared in high yields by the interaction of chalkones (in slight excess) and different ketones using BF3-etherate as cyclodehydrating agent or from 1,5-diketones in the presence of HBr and chalkone as hydrogen abstractor.The pyrylium cations have been converted into the corresponding nitrogen heterocycles (1-12;Z=N).
- Elshafie, Sayed M. M.
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p. 427 - 428
(2007/10/02)
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