N-alkoxypyridinium Salts Research Articles

Visible-Light-Induced Alkoxypyridylation of Alkenes Using N-Alkoxypyridinium Salts as Bifunctional Reagents.

Considering the ubiquitous presence of pyridine moieties in pharmaceutical compounds, it holds immense value to develop practical and straightforward methodologies for accessing heterocyclic aromatic hydrocarbons. In recent years, N-alkoxypyridinium salts have emerged as convenient radical precursors, enabling the generation of the corresponding alkoxy radicals and pyridine through single-electron transfer. Herein, we present the first report on visible-light-mediated intermolecular alkoxypyridylation of alkenes employing N-alkoxylpyridinium salts as bifunctional reagents with an exceptionally low catalyst loading (0.5 mol %).

Azolation of Benzylic C-H Bonds via Photoredox-Catalyzed Carbocation Generation.

A visible-light photoredox-catalyzed method is reported that enables the coupling between benzylic C-H substrates and N-H azoles. Classically, medicinally relevant N-benzyl azoles are produced via harsh substitution conditions between the azole and a benzyl electrophile in the presence of strong bases at high temperatures. Use of C-H bonds as the alkylating partner streamlines the preparation of these important motifs. In this work, we report the use of N-alkoxypyridinium salts as a critically enabling reagent for the development of a general C(sp3)-H azolation. The platform enables the alkylation of electron-deficient, -neutral, and -rich azoles with a range of C-H bonds, most notably secondary and tertiary partners. Moreover, the protocol is mild enough to tolerate benzyl electrophiles, thus offering an orthogonal approach to existing SN2 and cross-coupling methods.

Photoexcited Palladium-Initiated Remote Desaturation of N-Alkoxypyridinium Salts.

1,5-Hydrogen atom transfer (HAT) is an effective strategy to achieve remote desaturation of nonfunctionalized alkanes. Herein, we report a photoinduced remote desaturation reaction of N-alkoxypyridinium salts, which serve as alkoxyl radical precursors. Mechanistic studies show that a single electron transfer between the excited palladium complex and a N-alkoxypyridinium salt initiates a radical chain process leading to desaturation of N-alkoxypyridinium salts. This chain mechanism is supported by the measurement of the quantum yield of this reaction (Φ = 82). This reaction is applicable to a range of N-alkoxypyridinium salts, including some complex molecule-derived ones.

Visible-Light-Mediated Access to Phosphate Esters.

We report herein a practically simple visible-light photocatalytic approach for the synthesis of a large variety of phosphate esters through the combination of N-alkoxypyridinium salts and phosphites under mild conditions. The scope of the reaction is broad and the protocol was successfully applied to the synthesis of biologically relevant structures. Quantum yield measurements, as well as EPR experiments, allowed the suggestion of a reasonable reaction mechanism.

Remote C(sp3 )-H Arylation and Vinylation of N-Alkoxypyridinium Salts to δ-Aryl and δ-Vinyl Alcohols.

The reaction of readily available and bench-stable N-alkoxypyridinium salts with arylboronic and vinylboronic acids afforded δ-aryl and δ-vinyl alcohols, respectively, in the presence of fac-Ir(ppy)3 and Cu(OTf)2 dual catalysts. The reaction takes place through a domino process involving the reductive generation of alkoxyl radicals, 1,5-hydrogen atom transfer (1,5-HAT) and the copper-catalyzed cross-coupling reaction of the resulting translocated carbon radicals with boronic acids. Complementary to the Minisci reaction, this method allows for the arylation of nucleophilic alkyl radicals with both electron-rich and electron-poor arenes under mild reaction conditions.

Intermolecular Trapping of Alkoxyl Radicals with Alkenes: A New Route to Ether Synthesis

Alkoxyl radicals are highly reactive species which rapidly react by hydrogen atom transfer (HAT) or β-fragmentation to afford a carbon-centered radical. We discuss herein how these RO· radicals can be efficiently trapped in an intermolecular manner by styrene derivatives when they are generated by photoredox catalysis from the corresponding N-alkoxypyridinium salts. This allows for the synthesis of valuable ethers with complete anti-Markovnikov regioselectivity.1 Introduction2 Anti-Markovnikov Alkoxylation of Alkenes: Background3 Addition of Alkoxyl Radicals to Styrenes4 Summary and Outlook

Dual Photoredox/Copper Catalysis for the Remote C(sp3 )-H Functionalization of Alcohols and Alkyl Halides by N-Alkoxypyridinium Salts.

Under mild dual photoredox/copper catalysis, the reaction of N-alkoxypyridinium salts with readily available silyl reagents (TMSN3 , TMSCN, TMSNCS) afforded δ-azido, δ-cyano, and δ-thiocyanato alcohols in high yields. The reaction went through a domino process involving alkoxy radical generation, 1,5-hydrogen atom transfer (1,5-HAT) and copper-catalyzed functionalization of the resulting C-centered radical. Conditions for catalytic enantioselective δ-C(sp3 )-H cyanation were also documented.

Alkoxyl Radicals Generated under Photoredox Catalysis: A Strategy for anti-Markovnikov Alkoxylation Reactions.

Reported herein is a novel photoredox-catalyzed approach for ether synthesis and it involves alkoxyl radicals generated from N-alkoxypyridinium salts. A wide range of alkenes are smoothly difunctionalized in an anti-Markovnikov fashion, affording various functionalized alkyl alkyl ethers. Notably, this mild process tolerates a number of functional groups and is efficiently carried out under both batch and flow conditions. Importantly, electron paramagnetic resonance (EPR) experiments by spin trapping were carried out to characterize the radical intermediates involved in this radical/cationic process.

ChemInform Abstract: α-Hydroxyacylation of Pyridine.

Efficient synthesis of 2-α-hydroxyacylpyridines 10 starting from pyridine N-oxide and 2-bromoaldehydes via base-induced rearrangement of the resulting N-alkoxypyridinium salts 6 is described.

The synthesis of novel, visible-wavelength, oxidizable polymerization sensitizers based on the 8-halogeno-5,12-dihydroquinoxalino[2,3- b]quinoxaline skeleton

Novel dyes, based on the 8-halogeno-5,12-dihydroquinoxalino[2,3- b]quinoxaline skeleton, were synthesized and characterized using 1H NMR spectroscopy and chemical ionization mass spectroscopy. Their electrochemical and spectral properties, such as absorption and emission spectra, quantum yield of fluorescence and quantum yield of singlet oxygen generation, were also measured. These dyes were used as oxidizable sensitizers for diphenyliodonium and N-alkoxypyridinium salts. Photoredox pairs, consisting of dyes and pyridinium or iodonium salts, were found to be effective visible-wavelength initiators of free radical or cationic polymerization, respectively. The ability of each dye to act as a photoinitiator strongly depended upon its chemical structure. The heavy atoms present in the chemical structure could lead to excited triplet states within the dye, thereby facilitating electron transfer from these states.

Energetics of Electron-Transfer Reactions of Photoinitiated Polymerization: Dye-Sensitized Fragmentation of N-Alkoxypyridinium Salts

Electron transfer from excited dyes to N-alkoxypyridinium salts leads to reductive cleavage of the N−O bond to give an alkoxy radical that can be used to initiate polymerization. Bond-dissociation energies obtained from calculations based on density-functional theory are in agreement with predictions from a thermochemical cycle. These data show a difference of ca. 290 – 315 kJ/mol between the BDE of the pyridinium and that of the pyridyl radical and indicate that the fragmentation of the radical is highly exothermic. The energetic requirements for the photochemical electron transfer are discussed in terms of a simplified model that shows that the initiation efficiency of the radical polymerization can be correlated with a single parameter, the reduction potential of the sensitizing dye. Dyes from many classes and with absorption bands spanning the entire visible region were found to be effective in initiating photopolymerization of acrylate monomers in this system. Doubling of the photoresponse can be achieved through coupling of the reductive cleavage of the N-alkoxypyridinium with an oxidative cleavage of a C−B bond of an alkyltriarylborate, a process that utilizes the chemical potential stored in the oxidized dye following electron transfer to the pyridinium salt.

α‐Hydroxyacylation of pyridine

AbstractEfficient synthesis of 2‐α‐hydroxyacylpyridines 10 starting from pyridine N‐oxide and 2‐bromoaldehydes via base‐induced rearrangement of the resulting N‐alkoxypyridinium salts 6 is described.

Based-induced Conversion of N-Alkoxypyridinium Salts Bearing a Formyl Group in Their Alkoxyl Chain

Reaction of pyridine N-oxide with α-disubstituted 2-bromo-aldehydes led to the expected N-alkoxypyridinium salts which were converted to 2-(α-hydroxyacyl) pyridines on base treatment

ChemInform Abstract: A NOVEL MODE OF BASE‐INDUCED DECOMPOSITION OF N‐ALKOXYPYRIDINIUM SALTS

Chemischer InformationsdienstVolume 7, Issue 31 Preparative Organic Chemistry ChemInform Abstract: A NOVEL MODE OF BASE-INDUCED DECOMPOSITION OF N-ALKOXYPYRIDINIUM SALTS H. SLIWA, H. SLIWASearch for more papers by this authorA. TARTAR, A. TARTARSearch for more papers by this author H. SLIWA, H. SLIWASearch for more papers by this authorA. TARTAR, A. TARTARSearch for more papers by this author First published: August 3, 1976 https://doi.org/10.1002/chin.197631099Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume7, Issue31August 3, 1976 RelatedInformation

A novel mode of base-induced decomposition of N-alkoxypyridinium salts

A novel mode of base-induced decomposition of N-alkoxypyridinium salts

Mechanism of the base-catalyzed conversion of n-alkoxypyridinium salts to aldehydes

Mechanism of the base-catalyzed conversion of n-alkoxypyridinium salts to aldehydes

Chemistry of epoxides. XXVII. N-Alkoxypyridinium salts from amine oxides and epoxides. Preparation, reactions, and mechanism of base-induced decomposition

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTChemistry of epoxides. XXVII. N-Alkoxypyridinium salts from amine oxides and epoxides. Preparation, reactions, and mechanism of base-induced decompositionDaniel Swern and William N. MarmerCite this: J. Am. Chem. Soc. 1971, 93, 11, 2719–2727Publication Date (Print):June 1, 1971Publication History Published online1 May 2002Published inissue 1 June 1971https://doi.org/10.1021/ja00740a023RIGHTS & PERMISSIONSArticle Views140Altmetric-Citations11LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts