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Journal articles on the topic 'Pyridines'

Author: Grafiati

Published: 4 June 2021

Last updated: 30 July 2024

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1

McNally, Andrew, Ryan Dolewski, and Michael Hilton. "4-Selective Pyridine Functionalization Reactions via Heterocyclic Phosphonium Salts." Synlett 29, no. 01 (December 12, 2017): 08–14. http://dx.doi.org/10.1055/s-0036-1591850.

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Pyridines are widely used across the chemical sciences in applications ranging from pharmaceuticals, ligands for metal complex and battery technologies. Direct functionalization of pyridine C–H bonds is an important strategy to make useful pyridine derivatives, but there are few ways to selectively transform the 4-position of the scaffold. We recently reported that pyridines can be converted into heterocyclic phosphonium salts that can serve as generic handles for multiple subsequent bond-forming processes. Reactions with nucleophiles and transition-metal cross-couplings will be described to make C–O, C–S, C–N, and C–C bonds in a diverse range of pyridines including those embedded in complex pharmaceuticals.1 Introduction2 Direct, Regioselective Functionalization of Pyridines3 4-Position Selectivity via Metal Catalysis4 Versatile Functional Groups versus Specific Bond Constructions5 Phosphonium Salts as Reagents for Pyridine Functionalization6 Conclusions

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2

Czarnocki, Zbigniew, and Piotr Pomarański. "Arylpyridines: A Review from Selective Synthesis to Atropisomerism." Synthesis 51, no. 03 (December 14, 2018): 587–611. http://dx.doi.org/10.1055/s-0037-1611365.

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Multiply arylated heterocycles are interesting structures with highly useful functions and fascinating optoelectronic and biological properties. Pyridines are an important class of compounds, playing a role in various fields of chemistry. When the pyridine ring is connected to other aromatic systems, novel stereochemical outcomes may arise. This work summarizes different methodologies applied for the synthesis of substituted arylpyridine derivatives and summarizes stereochemical phenomena resulting from atropisomerism present in certain arylated pyridines.1 Introduction2 Arylpyridines Containing meta- and para-Substituted Phenyl Groups2.1 Arylpyridine Derivatives as Amphetamine Analogues Markers2.2 Site-Selective Synthesis of Arylpyridines3 Atropisomerism in Arylpyridines Containing ortho-Substituted Phenyl Groups3.1 Synthesis of Arylpyridines Containing ortho-Substituted Phenyl Groups3.2 Other Methods for the Preparation of Arylated Pyridines4 Fully Substituted Pyridine Derivatives4.1 Site-Selective Synthesis of Fully Arylated Pyridines4.3 Atropisomerism in Densely Substituted Arylpyridines Containing ortho-Substituted Phenyl Groups5 Enantioselective Synthesis of Arylpyridine Derivatives6 Conclusion

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3

Zhang, Li-Juan, Qun Wu, Jing Sun, and Chao-Guo Yan. "Synthesis of functionalized spiro[indoline-3,4’-pyridines] and spiro[indoline-3,4’-pyridinones] via one-pot four-component reactions." Beilstein Journal of Organic Chemistry 9 (May 2, 2013): 846–51. http://dx.doi.org/10.3762/bjoc.9.97.

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In the presence of triethylamine as catalyst, the one-pot four-component reactions of arylamines, methyl propiolate, isatin and malononitrile afforded the functionalized spiro[indoline-3,4’-pyridine] derivatives in good yields. Similar reactions with ethyl cyanoacetate successfully afforded the functionalized spiro[indoline-3,4’-pyridines] and spiro[indoline-3,4’-pyridinones] as the main products according to the structures of the arylamines and other primary amines.

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4

Brugarolas, P., R. Freifelder, S. H. Cheng, and O. DeJesus. "Synthesis of meta-substituted [18F]3-fluoro-4-aminopyridine via direct radiofluorination of pyridine N-oxides." Chemical Communications 52, no. 44 (2016): 7150–52. http://dx.doi.org/10.1039/c6cc02362b.

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Fluorination and radiofluorination of pyridines is challenging, especially in meta position. Here we describe a new chemical reaction to generate meta fluorinated pyridines: halogen substitution on pyridine N-oxides followed by reduction.

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5

Balkenhohl, Moritz, and Paul Knochel. "Regioselective C–H Activation of Substituted Pyridines and other Azines using Mg- and Zn-TMP-Bases." SynOpen 02, no. 01 (January 2018): 0078–95. http://dx.doi.org/10.1055/s-0036-1591966.

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The metalation of substituted pyridines, diazines and related N-heterocycles using TMPMgCl·LiCl, TMP2Mg·2LiCl, TMPZnCl·LiCl or TMP2Zn·2LiCl2·2MgCl2 (TMP = 2,2,6,6-tetramethylpiperidyl) in the presence or absence of a Lewis acid is reviewed. Contents 1 Introduction2 Magnesiation of Pyridines and Related Azines2.1 Magnesiations using TMPMgCl·LiCl2.2 Magnesiations using TMP2Mg·2LiCl and Related Bases2.3 BF3·OEt2 Promoted Metalations of Pyridines3 Zincation of Pyridines and Related Azines using TMPZnCl·LiCl and TMP2Zn·2LiCl·2MgCl2 4 Metalation of Pyridines using other TMP-Bases5 Magnesiation and Zincation of Diazines6 Conclusion

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6

Mallisetty, Naga Mohan, Hanumantharao Ganipisetti, Debendra Majhi, and Venkata Nagendra Kumar Putta. "Design, Synthesis of Some New Scaffolds based on Pyrrolyl-Pyridines as Potential Anticancer Agents." Asian Journal of Chemistry 35, no. 2 (2023): 468–74. http://dx.doi.org/10.14233/ajchem.2023.23974.

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Pyrrolyl-pyridine heterocyclic compounds have received considerable attention because of its unique bioisosteric properties and an unusually wide spectrum of biological activities. Thus, it is a perfect framework for the synthesis of novel C–N, C–C bond formations like 5-substituted-1-benzyl-1Hpyrrolo[ 2,3-b]pyridines (3), 2-(1H-pyrrolo[2,3-b]pyridin-5-yl)phenol (5) and screened for their anticancer activity. The synthesized compounds were characterized by 1H NMR, 13C NMR, IR, mass spectral techniques and elemental analysis. The outcomes of these compounds 2,6-difluorobenzylpyrrolidin- 1H-pyrrolo[2,3-b]pyridine, 2,6-difluorobenzyl-N,N-dimethyl-1H-pyrrolo[2,3-b]-pyridin-5-amine had a signicant anticancer activity against human cervical cancer cell line (Hela) with IC50 4.8, 9.7 μg/mL and whereas pyrrolo[2,3-b]pyridin-5-phenol, pyrrolo[2,3-b]pyridin-5-vinylphenol are active against human breast cancer cell line (MCF-7) with IC50 8.1, 3.2 μg/mL, respectively.

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7

Gad-Elkareem, Mohamed A. M., Azza M. Abdel-Fattah, and Mohamed A. A. Elneairy. "Pyrazolo[3,4-b]pyridine in heterocyclic synthesis: synthesis of new pyrazolo[3,4-b]pyridines, imidazo[1',2':1,5]pyrazolo[3,4-b]pyridines, and pyrido[2',3':3,4]pyrazolo[1,5-a]pyrimidines." Canadian Journal of Chemistry 85, no. 9 (September 1, 2007): 592–99. http://dx.doi.org/10.1139/v07-089.

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Pyrazolo[3,4-b]pyridine derivatives 7 and 9 were synthesized via the reaction of 3-amino-1H-pyrazolo-[3,4-b]pyridine derivative 2 with ω-bromoacetophenones. Reaction of 7 and 9 with Ac2O afforded the imidazo[1',2':1,5]py razolo[3,4-b]pyridine derivative 8 and pyrazolo[3,4-b]pyridine derivative 10, respectively. Reaction of 2 with chloroacetonitrile followed by DMF-DMA gave imidazo[1',2':1,5]pyrazolo[3,4-b]pyridines 4 and 5, respectively. Acetyl acetone and 1,1-dicyano-2,2-dimethylthioethene were reacted with 2 to afford the pyrido[2',3':3,4]pyrazolo-[1,5-a]-pyrimidines 11 and 14, respectively. Also, 2 reacted with DMF-DMA to yield the formamidine 15, which in turn, reacted with active methylene reagents, yielding the corresponding pyrido[2',3':3,4]pyrazolo[1,5-a]pyrimidines 18 and 23a-23d.Key words: 1H-pyrazolo[3,4-b]pyridines, imidazo[1',2':1,5]pyrazolo[3,4-b]pyridines, pyrido[2',3':3,4]pyrazolo[1,5-a]pyrimidines.

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8

Preston, Dan, Samantha M. McNeill, James E. M. Lewis, Gregory I. Giles, and James D. Crowley. "Enhanced kinetic stability of [Pd2L4]4+ cages through ligand substitution." Dalton Transactions 45, no. 19 (2016): 8050–60. http://dx.doi.org/10.1039/c6dt00133e.

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[Pd₂(tripy)₄]⁴⁺ cage architectures (where tripy = 2,6-bis(pyridin-3-ylethynyl)pyridine) were made more kinetically robust in the presence of range of nucleophiles by the addition of amino groups in either the 2-(2A-tripy) or 3-(3A-tripy) positions of the tripy ligands' terminal pyridines, with the [Pd₂(2A-tripy)₄]⁴⁺ cage proving the most stable.

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9

Barlin, GB. "Heterocyclic Amplifiers of Phleomycin. VIII. Mono- Bis-(5'-substituted 1',3',4'-thiadiazol-2'-yl)pyridines and Mono(5'-substituted 1',3',4'-thiadiazol-2'-ylmethyl)pyridines." Australian Journal of Chemistry 38, no. 10 (1985): 1491. http://dx.doi.org/10.1071/ch9851491.

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A series of mono- and bis -(5′-substituted 1′,3′,4′-thiadiazol-2′- yl )pyridines with strongly basic side chains, e.g., 3,5-bis[5′(2′-N,N- dimethylaminoethylthio )-1′,3′,4′-thiadiazol-2′-yl]pyridine (1), and (5?-substituted 1′,3′,4′-thiadiazol-2′-ylmethyl)pyridines have been prepared for evaluation as amplifiers of phleomycin. Five of the six bis (5′-substituted 1′,3′,4′-thiadiazol-2′-yl)pyridines were themselves antibacterial under the test conditions, but compound (1) and the mono(5′-substituted 1′,3′,4′-thiadiazol-2′-yl)-pyridines and -methylpyridines displayed moderate two-to-three-star activity.

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10

Schmitt, Martine, Jean-Jacques Bourguignon, Gordon B. Barlin, and Les P. Davies. "Imidazo[1,2-b]pyridazines. XXIII Some 5-Deaza Analogues. Syntheses of Some 2-Aryl-6-(chloro, methoxy or unsubstituted)-3- (variously substituted)imidazo[1,2-a]pyridines and Their Affinity for Central and Mitochondrial Benzodiazepine Receptor." Australian Journal of Chemistry 50, no. 7 (1997): 719. http://dx.doi.org/10.1071/c97004.

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The syntheses of ethyl {2′-aryl-6′-(chloro, methoxy and unsubstituted)imidazo[1,2-a]pyridin-3′-yl}-2- (acylamino, acetoxy and hydroxy)acetates, 3-benzamidomethyl-2-benzoyl-6-(chloro and methoxy)imidazo-[1,2-a]pyridines, 3-amino-6-chloro-2-phenylimidazo[1,2-a]pyridine and ethyl 2-(2′-phenylimidazo[1,2-a]pyridin-3′-yl)acetate are reported. The ability of these compounds to displace [3H]diazepam from central and mitochondrial (peripheral-type) benzodiazepine receptors has been examined. Ethyl 2-benzamido-2-{6′-chloro-2′-(4′′-chlorophenyl)imidazo[1,2-a]pyridin-3′-yl} acetate (21) was selective for peripheral-type receptors (IC5013 nM) but none bound strongly to central receptors.

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11

Bertuzzi, Giulio, Luca Bernardi, and Mariafrancesca Fochi. "Nucleophilic Dearomatization of Activated Pyridines." Catalysts 8, no. 12 (December 6, 2018): 632. http://dx.doi.org/10.3390/catal8120632.

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Amongst nitrogen heterocycles of different ring sizes and oxidation statuses, dihydropyridines (DHP) occupy a prominent role due to their synthetic versatility and occurrence in medicinally relevant compounds. One of the most straightforward synthetic approaches to polysubstituted DHP derivatives is provided by nucleophilic dearomatization of readily assembled pyridines. In this article, we collect and summarize nucleophilic dearomatization reactions of - pyridines reported in the literature between 2010 and mid-2018, complementing and updating previous reviews published in the early 2010s dedicated to various aspects of pyridine chemistry. Since functionalization of the pyridine nitrogen, rendering a (transient) pyridinium ion, is usually required to render the pyridine nucleus sufficiently electrophilic to suffer the attack of a nucleophile, the material is organized according to the type of N-functionalization. A variety of nucleophilic species (organometallic reagents, enolates, heteroaromatics, umpoled aldehydes) can be productively engaged in pyridine dearomatization reactions, including catalytic asymmetric implementations, providing useful and efficient synthetic platforms to (enantioenriched) DHPs. Conversely, pyridine nitrogen functionalization can also lead to pyridinium ylides. These dipolar species can undergo a variety of dipolar cycloaddition reactions with electron-poor dipolarophiles, affording polycyclic frameworks and embedding a DHP moiety in their structures.

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12

Wójcicka, Anna, and Aleksandra Redzicka. "An Overview of the Biological Activity of Pyrrolo[3,4-c]pyridine Derivatives." Pharmaceuticals 14, no. 4 (April 11, 2021): 354. http://dx.doi.org/10.3390/ph14040354.

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Pyrrolo[3,4-c]pyridine is one of the six structural isomers of the bicyclic ring system containing a pyrrole moiety fused to a pyridine nucleus. The broad spectrum of pharmacological properties of pyrrolo[3,4-c]pyridine derivatives is the main reason for developing new compounds containing this scaffold. This review presents studies on the biological activity of pyrrolo[3,4-c]pyridines that have been reported in the scientific literature. Most of these derivatives have been studied as analgesic and sedative agents. Biological investigations have shown that pyrrolo[3,4-c]pyridines can be used to treat diseases of the nervous and immune systems. Their antidiabetic, antimycobacterial, antiviral, and antitumor activities also have been found.

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13

Bastrakov, Maxim A., Alexey K. Fedorenko, Alexey M. Starosotnikov, Ivan V. Fedyanin, and Vladimir A. Kokorekin. "Synthesis and Facile Dearomatization of Highly Electrophilic Nitroisoxazolo[4,3-b]pyridines." Molecules 25, no. 9 (May 8, 2020): 2194. http://dx.doi.org/10.3390/molecules25092194.

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A number of novel 6-R-isoxazolo[4,3-b]pyridines were synthesized and their reactions with neutral C-nucleophiles (1,3-dicarbonyl compounds, π-excessive (het)arenes, dienes) were studied. The reaction rate was found to be dependent on the nature of the substituent 6-R. The most reactive 6-nitroisoxazolo[4,3-b]pyridines are able to add C-nucleophiles in the absence of a base under mild conditions. In addition, these compounds readily undergo [4+2]-cycloaddition reactions on aromatic bonds C=C(NO2) of the pyridine ring, thus indicating the superelectrophilic nature of 6-NO2-isoxazolo[4,3-b]pyridines.

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14

Frohn, Hermann Josef, Thorsten Schroer, and Gerald Henkel. "Koordinationsverhalten des Pentafluorphenylxenonium Salzes [C6F5Xe]+[AsF6]- gegenüber Pyridinen unterschiedlicher Basizität / Co-ordinative Behaviour of the Pentafluorophenylxenonium Salt [C6F5Xe]+[AsF6]- to Pyridines of Different Basicity." Zeitschrift für Naturforschung B 50, no. 12 (December 1, 1995): 1799–810. http://dx.doi.org/10.1515/znb-1995-1206.

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The arylxenonium cation in the salt [C6F5Xe]+ [AsF6]- is isoelectronic to C6F5I, but coordinatively unsaturated with respect to N-bases like MeCN and pyridines. Co-ordination of strongly basic pyridines causes weakening of the Xe-C bond and C6F1 radical formation. The thermal decomposition of pyridine co-ordinated arylxenonium cations gives three groups of products: C-pentafluorophenylated pyridines, N-pentafluorophenylated pyridinium and N-protonated pyridinium salts. The co-ordination ability of the different pyridines shows a good correlation (C6F5 group) with the 19F NMR shift values of the p-F atom and the coupling constants 3J (19F-129Xe). An X-ray structure analysis was performed for the co-ordination product [C6F5Xe · 2,6-C5H3F2N ]+ [AsF6]- and for [C6F5-C5H5N]+ [(C6F5)2BF2]-, which was obtained by thermolysis of the corresponding adduct.

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15

Kubík, Richard, Stanislav Böhm, Iveta Ruppertová, and Josef Kuthan. "Sterically Crowded Heterocycles. III. A General Approach to Imidazo[1,2-a]pyridines by Ferricyanide Oxidation of Quaternary Pyridinium Salts." Collection of Czechoslovak Chemical Communications 61, no. 1 (1996): 126–38. http://dx.doi.org/10.1135/cccc19960126.

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Substituted 1-(pyridin-2-yl)-2,4,6-triphenylpyridinium perchlorates 1b-1e were converted with potassium ferricyanide and potassium hydroxide to sterically crowded 2-phenyl-3-[(Z)-1,3-diphenyl-3-oxopropenyl]imidazo[1,2-a]pyridines 2b-2e accompanied by minor isomeric 2-benzoyl-3,5-diphenyl-1-(pyridin-2-yl)pyrroles 3c-3e. 4-Phenyl-2,6-di(4-substituted phenyl)-1-(pyridin-2-yl)pyridinium salts 4a, 4b gave exclusively corresponding imidazo[1,2-a]pyridines 5a, 5b while the ferricyanide oxidation of 1-(5-iodo- and 5-cyanopyridin-2-yl)-2,4,6-triphenylpyridinium perchlorates 6a, 6b led to mixtures of major imidazo[1,2-a]pyridines 7a-7c and minor pyrroles 8a-8c. Some mechanistic aspects of the oxidation procedure are discussed in connection with a resistance of 2,6-diphenyl-1,3,5-trimethylpyridinium perchlorate (9c) towards the oxidizing agents.

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16

Nikol’skiy, Vladislav V., Mikhail E. Minyaev, Maxim A. Bastrakov, and Alexey M. Starosotnikov. "Mild and efficient synthesis and base-promoted rearrangement of novel isoxazolo[4,5-b]pyridines." Beilstein Journal of Organic Chemistry 20 (May 14, 2024): 1069–75. http://dx.doi.org/10.3762/bjoc.20.94.

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An efficient method for the synthesis of isoxazolo[4,5-b]pyridines has been developed on the basis of readily available 2-chloro-3-nitropyridines via the intramolecular nucleophilic substitution of the nitro group as a key step. The previously unknown base-promoted Boulton–Katritzky rearrangement of isoxazolo[4,5-b]pyridine-3-carbaldehyde arylhydrazones into 3-hydroxy-2-(2-aryl[1,2,3]triazol-4-yl)pyridines was observed.

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17

Xin, Zhi Jun, Zhong Jia, Dian He, Jian Ping Liang, Lei Tao, Xue Hu Li, and Xi Hong Lu. "Study on N-(pyridin-4-Yl) Salicylamides as Antimycobacterial Agents." Advanced Materials Research 634-638 (January 2013): 1371–75. http://dx.doi.org/10.4028/www.scientific.net/amr.634-638.1371.

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A series of N-(pyridin-4-yl) salicylamides derivatives were prepared through acylation of the corresponding acetylsalicyloyl chlorides with substituted 4-amino-pyridines. These compounds were evaluated in vitro for antimycobacterial activities against Mycobacterium tuberculosis (TB) and Mycobacterium avium (A) by the minimum inhibitory concentrations (MIC) values. Eight of the compounds exhibited lower MIC against A than isoniazide (INH). Meanwhile, four of the compounds exhibited good anti-TB activity, when they were compared with INH. Antimycobacterial activities of N-(pyridin-4-yl) salicylamides were influenced by the balance between hydrophobicity and electron-withdrawing substituent effect on the phenyl and pyridine ring. These studies show that these compounds might serve as prospective wide-spectrum antimycobacterial substances.

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18

Wei, Hongbo, and Yun Li. "Quick Access to Pyridines through 6π-3-Azatriene Electrocyclization: Concise Total Synthesis of Suaveoline Alkaloids." Synlett 30, no. 14 (April 15, 2019): 1615–20. http://dx.doi.org/10.1055/s-0037-1611811.

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Pyridine is a prevalent structural heterocyclic motifs in natural products, pharmaceuticals, and advanced materials. Several different methodologies have been developed for the synthesis of these kinds of molecules. However, a sustainable and efficient procedure for the synthesis of pyridines is still highly desirable. In this Synpacts article, we highlight our recent approach to the construction of highly substituted pyridines though a tandem condensation/alkyne isomerization/6π-3-azatriene electrocyclization sequence. The present protocol was used to synthesize a series of polysubstituted pyridines (30 examples) in moderate to good yields. The process also permitted the development of a concise strategy for collective total syntheses of suaveoline, norsuaveoline, and macrophylline.

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19

Forgione, Pat, Fei Chen, Franklin Chacón-Huete, and Hassan El-Husseini. "Convenient and Inexpensive Route to Sulfonylated Pyridines via SNAr Reaction of Electron-Rich Pyridines by Iron Catalysis." Synthesis 50, no. 09 (February 20, 2018): 1914–20. http://dx.doi.org/10.1055/s-0036-1591541.

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Sulfonylated pyridines were synthesized in moderate to excellent yields, with a wide scope of substituted pyridines and sulfinate salts as starting materials, by an iron-catalyzed SNAr reaction. This new methodology exhibits advantages for the synthesis of these useful substrates, such as the use of a readily available, inexpensive catalyst, prevention of the disproportionation of the sulfinate salts, and, more importantly, providing access to electron-rich pyridine substrates.

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20

Werstiuk, Nick Henry, and Chen Ju. "Protium–deuterium exchange of substituted pyridines in neutral D2O at elevated temperatures." Canadian Journal of Chemistry 67, no. 1 (January 1, 1989): 5–10. http://dx.doi.org/10.1139/v89-002.

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H–D exchange of a series of pyridines 1–15, 10H-pyridino[3,2-b][1,4]benzothiazine (16), phenothiazine (17), and aniline has been carried out in neutral D2O at elevated temperatures. The substrates undergo selective exchange and are generally isolated in good yield. Cyanopyridines 4,5, and 6 hydrolyze readily in D2O at elevated temperatures, and the resultant carboxylic acids decarboxylate. This reaction provides a convenient one-step route to selectively labelled pyridines. Possible mechanisms of exchange are presented. Keywords: protium–deuterium exchange, substituted pyridines, temperature effect

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21

Razmienė, Beatričė, Eva Řezníčková, Vaida Dambrauskienė, Radek Ostruszka, Martin Kubala, Asta Žukauskaitė, Vladimír Kryštof, Algirdas Šačkus, and Eglė Arbačiauskienė. "Synthesis and Antiproliferative Activity of 2,4,6,7-Tetrasubstituted-2H-pyrazolo[4,3-c]pyridines." Molecules 26, no. 21 (November 8, 2021): 6747. http://dx.doi.org/10.3390/molecules26216747.

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A library of 2,4,6,7-tetrasubstituted-2H-pyrazolo[4,3-c]pyridines was prepared from easily accessible 1-phenyl-3-(2-phenylethynyl)-1H-pyrazole-4-carbaldehyde via an iodine-mediated electrophilic cyclization of intermediate 4-(azidomethyl)-1-phenyl-3-(phenylethynyl)-1H-pyrazoles to 7-iodo-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridines followed by Suzuki cross-couplings with various boronic acids and alkylation reactions. The compounds were evaluated for their antiproliferative activity against K562, MV4-11, and MCF-7 cancer cell lines. The most potent compounds displayed low micromolar GI50 values. 4-(2,6-Diphenyl-2H-pyrazolo[4,3-c]pyridin-7-yl)phenol proved to be the most active, induced poly(ADP-ribose) polymerase 1 (PARP-1) cleavage, activated the initiator enzyme of apoptotic cascade caspase 9, induced a fragmentation of microtubule-associated protein 1-light chain 3 (LC3), and reduced the expression levels of proliferating cell nuclear antigen (PCNA). The obtained results suggest a complex action of 4-(2,6-diphenyl-2H-pyrazolo[4,3-c]pyridin-7-yl)phenol that combines antiproliferative effects with the induction of cell death. Moreover, investigations of the fluorescence properties of the final compounds revealed 7-(4-methoxyphenyl)-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridine as the most potent pH indicator that enables both fluorescence intensity-based and ratiometric pH sensing.

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22

Heineking, N., H. Dreizler, and R. Schwarz. "Nitrogen and Deuterium Hyperfine Structure in the Rotational Spectra of Pyridine and [4-D] Pyridine." Zeitschrift für Naturforschung A 41, no. 10 (October 1, 1986): 1210–13. http://dx.doi.org/10.1515/zna-1986-1005.

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We reanalysed the 14N hyperfine structure in the rotational spectra of pyridine and [4-D]- pyridine with higher precision and determined the D quadrupole coupling. It is intended to provide a reference for comparison with substituted pyridines.

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23

Ramesha, Ajjahalli B., Nagarakere C. Sandhya, Chottanahalli S. Pavan Kumar, Mahanthawamy Hiremath, Kempegowda Mantelingu, and Kanchugarakoppal S. Rangappa. "A novel approach for the synthesis of imidazo and triazolopyridines from dithioesters." New Journal of Chemistry 40, no. 9 (2016): 7637–42. http://dx.doi.org/10.1039/c6nj01038e.

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24

Bakke, J. M. "Nitropyridines: Synthesis and reactions." Pure and Applied Chemistry 75, no. 10 (January 1, 2003): 1403–15. http://dx.doi.org/10.1351/pac200375101403.

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Reaction of pyridine and substituted pyridines with N2O5 in an organic solvent gives the N-nitropyridinium ion. When this is reacted with SO2/HSO3– in water, 3-nitropyridine is obtained (77 % yield). With substituted pyridines, the method gives good yields for 4-substituted and moderate yields for 3-substituted pyridines. The reaction mechanism is not an electrophilic aromatic substitution, but one in which the nitro group migrates from the 1-position to the 3-position by a [1,5 ] sigmatropic shift. From 4-aminopyridine, imi- dazo [4,5-c ] pyridines have been synthesized. From 3-nitropyridine, 5-nitropyridine-2-sulfonic acid is formed in a two-step reaction. From this, a series of 2-substituted-5-nitro-pyridines has been synthesized. 3-Nitropyridine and 4-substituted-3-nitropyridines have been substituted with ammonia and amines by the vicarious substitution method and by the oxidative substitution method in the position para to the nitro group. High regioselectivities and yields have been obtained in both cases to afford a series of 4-substituted-2-alkylamino-5-nitropyridines.

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25

Prek, Benjamin, Uroš Grošelj, Marta Kasunič, Silvo Zupančič, Jurij Svete, and Branko Stanovnik. "Reactions of Methyl Ketones and (Hetero)arylcarboxamides with N,N-Dimethylacetamide Dimethyl Acetal. A Simple Metal-Free Synthesis of 2,4,6-Trisubstituted Pyridines." Australian Journal of Chemistry 68, no. 2 (2015): 184. http://dx.doi.org/10.1071/ch14349.

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Two metal-free syntheses of 2,4,6-trisubstituted pyridines 10a–m and 16a–j are described. N,N,6-Trimethyl-4-(substituted)pyridin-2-amines 10 were prepared from aryl or heteroaryl methyl ketones which were transformed with N,N-dimethylacetamide dimethyl acetal (DMADMA) into enaminones 4a–m, followed by treatment with ammonium acetate to give (Z)-3-amino-1-(substituted)but-2-en-1-ones 5a–m. These were treated with DMADMA under microwave irradiation in a closed vessel at 130°C, to give via intermediates 7–9 the final products 10a–m. N2,N2,N4,N4-Tetramethyl-6-(substituted) pyridine-2,4-diamines 16a–j were prepared in a one-pot synthesis from the corresponding carboxamides 11a–j by treatment with an excess of DMADMA in a closed vessel under microwave irradiation to give via intermediates 12a–j to 15a–j the final products 16a–j. X-Ray single crystal diffractometry studies of the enaminones 5c, 5g, 5i, 5j, and 5m and 2,4,6-trisubstituted pyridines 16a, 16b, 16g, 16i, and 16j were consistent with the expected structures.

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Comparini, Lucrezia Margherita, and Mauro Pineschi. "Recent Progresses in the Catalytic Stereoselective Dearomatization of Pyridines." Molecules 28, no. 17 (August 22, 2023): 6186. http://dx.doi.org/10.3390/molecules28176186.

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1,2- and 1,4-dihydropyridines and N-substituted 2-pyridones are very important structural motifs due to their synthetic versatility and vast presence in a variety of alkaloids and bioactive molecules. In this article, we gather and summarize the catalytic and stereoselective synthesis of partially hydrogenated pyridines and pyridones via the dearomative reactions of pyridine derivatives up to mid-2023. The material is fundamentally organized according to the type of reactivity (electrophilic/nucleophilic) of the pyridine nucleus. The material is further sub-divided taking into account the nucleophilic species when dealing with electrophilic pyridines and considering the reactivity manifold of pyridine derivatives behaving as nucleophiles at the nitrogen site. The latter more recent approach allows for an unconventional entry to chiral N-substituted 2- and 4-pyridones in non-racemic form.

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27

Shen, Qun, Huoji Chen, Ling Qin, Hui-bin Wu, and Lidong Weng. "Aerobic Iron(III)-Catalyzed Direct Thiolation of Imidazo[1,2-a]pyridine with Thiols." SynOpen 04, no. 02 (April 2020): 17–22. http://dx.doi.org/10.1055/s-0040-1707517.

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A novel and efficient iron(III)-catalyzed regioselective C-3 sulfenylation of imidazo[1,2-a]pyridines with thiols under oxygen atmosphere has been developed. The reaction proceeds in moderate to good yields with a broad range of substrates, providing a novel, efficient and green route for accessing synthetically useful C3-sulfenated imidazo-[1,2-a]pyridines. Moreover, the fluoride-containing C3-sulfenated imidazo-[1,2-a]pyridine 3ai exhibited superior anticancer activity and good safety profiles.

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28

Yakovenko, G. G., and M. V. Vovk. "Convenient approaches to the synthesis of 6-amino- and 6-oxoimidazo[4,5-b]pyrazolo[3,4-e]pyridines." Journal of Organic and Pharmaceutical Chemistry 19, no. 1(73) (March 15, 2021): 10–15. http://dx.doi.org/10.24959/ophcj.21.224583.

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Aim. To develop convenient approaches to the synthesis of 6-amino- and 6-oxoimidazo[4,5-b]pyrazolo[3,4-e]pyridines as promising biologically active scaﬀolds.Results and discussion. It has been found that cyclocondensation of N-Boc-4-aminopyrazole-5-carbaldehydes with creatinine can be used as an eﬀective method for obtaining 6-aminoimidazo[4,5-b]pyrazolo[3,4-e]pyridines previously unknown. For the synthesis of their 6-oxoanalogs, the reaction of 5-aminopyrazolo[4,3-b]pyridine-6-carboxylic acids used in a modifed Curtius rearrangement with diphenylphosphorylazide was successful. This method was implemented through the stage of the intermediate aminoisocyanates formation.Experimental part. The reaction of N-Boc-4-aminopyrazole-5-carbaldehydes with creatinine in the presence of pyrrolidine as a catalyst in reﬂuxing acetic acid allowed to obtain 6-aminoimidazo[4,5-b]pirazolo[3,4-e]pyridines with the yields of 54 – 70 %. The structure of the compounds synthesized was proven by spectral measurements. In the 1H NMR spectra there were singlets of H-3 (7.63 – 7.88 ppm) and H-8 (7.87 – 8.26 ppm) protons, as well as broad singlets of the NH2 group in the range of 7.05 – 7.21 ppm. Heating of 5-aminopyrazolo[4,3-b]pyridine-6-carboxylic acids with triethylamine and diphenylphosphorylazide in dioxane for 6 hours gave 1-substituted imidazo[4,5-b]pyrazolo[3,4-е]pyridine-6(5Н)-ones with the yields of 67 – 80 %. The IR-spectra of the compounds synthesized were characterized by the absorption bands of the C=O (1705 – 1708 cm-1) and NH (3275 – 3281 cm-1) groups. 1H NMR-spectra were characterized by singlets of H-3 and H-8 protons in the intervals of 7.43 – 8.08 ppm and 7.92 – 8.32 ppm respectively, as well as by two broad singlets of NH-protons in the ranges of 10.90 – 11.12 ppm and 11.25 – 11.37 ppm.Conclusions. Eﬀective approaches to the synthesis of new promising heterocyclic systems of 6-amino- and6-oxoimidazo[4,5-b]pirazolo[3,4-e]pyridines have been developed. Cyclocondensations of N-Boc-4-aminopyrazole-5-carbaldehydes with creatinine and 5-aminopyrazolo[4,3-b]pyridine-6-carboxylic acids with diphenylphosphorylazide have been proven to be convenient ways to obtain these compounds with good yields.Key words: N-Boc-4-aminopyrazole-5-carbaldehyde; creatinine; 5-aminopyrazolo[4,3-b]pyridine-6-carboxylic acid; diphenylphosphorylazide; 6-amino(oxo)imidazo[4,5-b]pyrazolo[3,4-e]pyridines;cyclocondensation

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29

Yang, Kai, Cai-Bo Chen, Zhao-Wen Liu, Zhen-Lin Li, Yu Zeng, and Zhao-Yang Wang. "C3-Alkylation of Imidazo[1,2-a]pyridines via Three-Component Aza-Friedel–Crafts Reaction Catalyzed by Y(OTf)3." Molecules 29, no. 15 (July 24, 2024): 3463. http://dx.doi.org/10.3390/molecules29153463.

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As an important class of nitrogen-containing fused heterocyclic compounds, imidazo[1,2-a]pyridines often exhibit significant biological activities, such as analgesic, anticancer, antiosteoporosis, anxiolytic, etc. Using Y(OTf)3 as a Lewis acid catalyst, a simple and efficient method has been developed for the synthesis of C3-alkylated imidazo[1,2-a]pyridines through the three-component aza-Friedel–Crafts reaction of imidazo[1,2-a]pyridines, aldehydes, and amines in the normal air atmosphere without the protection of inert gas and special requirements for anhydrous and anaerobic conditions. A series of imidazo[1,2-a]pyridine derivatives were obtained with moderate to good yields, and their structures were confirmed by 1H NMR, 13C NMR, and HRMS. Furthermore, this conversion has the advantages of simple operation, excellent functional group tolerance, high atomic economy, broad substrate scope, and can achieve gram-level reactions. Notably, this methodology may be conveniently applied to the further design and rapid synthesis of potential biologically active imidazo[1,2-a]pyridines with multifunctional groups.

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30

Laxmi, Dandamudi Sri, Suryadevara V. Vardhini, Venkata R. Guttikonda, Mandava V. B. Rao, and Manojit Pal. "Synthesis of 2-substituted Furo[3,2-b]pyridines Under Pd/C-Cu Catalysis Assisted by Ultrasound: Their Evaluation as Potential Cytotoxic Agents." Anti-Cancer Agents in Medicinal Chemistry 20, no. 8 (July 24, 2020): 932–40. http://dx.doi.org/10.2174/1871520620666200311102304.

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Background: Compounds containing furo[3,2-b]pyridine framework have shown interesting pharmacological properties, including anticancer activities. Though these compounds are generally synthesized via the heteroannulation processes involving acetylenic derivatives, some of them are complex. Objective: The study aimed to explore a series of 2-substituted furo[3,2-b]pyridines for their cytotoxic properties against cancer cell lines in vitro. Methods: We developed a convenient synthesis of 2-substituted furo[3,2-b]pyridines via sequential (i) C-C coupling followed by (ii) C-O bond-forming reactions in a single pot. The reactions were performed under ultrasound irradiation in the presence of Pd/C as an inexpensive, stable and widely used catalyst. A range of 2- substituted furo[3,2-b]pyridines were synthesized via coupling of 3-chloro-2-hydroxy pyridine with terminal alkynes in the presence of 10% Pd/C-CuI-PPh3-Et3N in EtOH. The in vitro evaluation of all these compounds was carried out against MDA-MB-231 and MCF-7 cell lines and subsequently against SIRT1. Results: The furo[3,2-b]pyridine derivative 3b showed encouraging growth inhibition of both MDAMB-231 and MCF-7 cell lines and inhibition of SIRT1. The compound 3b also showed apoptosis-inducing potential when tested against MCF-7 cells. Conclusion: The Pd/C-Cu catalysis under ultrasound accomplished a one-pot and direct access to 2-substituted furo[3,2-b]pyridine derivatives, some of which showed anticancer properties.

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31

Śliwa, Wanda, and Małgorzata Deska. "Platinum(II) Complexes of Pyridines. A Review." Collection of Czechoslovak Chemical Communications 64, no. 3 (1999): 435–58. http://dx.doi.org/10.1135/cccc19990435.

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The chemistry of platinum(II) complexes of pyridine and related compounds is reviewed. Also the oxidative addition reaction to platinum(II) complexes of pyridines, as a method of conversion of Pt(II) into Pt(IV) species is described. A review with 90 references.

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32

Donaire-Arias, Ana, Ana Maria Montagut, Raimon Puig de la Bellacasa, Roger Estrada-Tejedor, Jordi Teixidó, and José I. Borrell. "1H-Pyrazolo[3,4-b]pyridines: Synthesis and Biomedical Applications." Molecules 27, no. 7 (March 30, 2022): 2237. http://dx.doi.org/10.3390/molecules27072237.

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Pyrazolo[3,4-b]pyridines are a group of heterocyclic compounds presenting two possible tautomeric forms: the 1H- and 2H-isomers. More than 300,000 1H-pyrazolo[3,4-b]pyridines have been described which are included in more than 5500 references (2400 patents) up to date. This review will cover the analysis of the diversity of the substituents present at positions N1, C3, C4, C5, and C6, the synthetic methods used for their synthesis, starting from both a preformed pyrazole or pyridine, and the biomedical applications of such compounds.

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33

Mu, Bing, Yusheng Wu, Jingya Li, Dapeng Zou, Junbiao Chang, and Yangjie Wu. "An unprecedented Pd-catalyzed decarboxylative coupling reaction of aromatic carboxylic acids in aqueous medium under air: synthesis of 3-aryl-imidazo[1,2-a]pyridines from aryl chlorides." Organic & Biomolecular Chemistry 14, no. 1 (2016): 246–50. http://dx.doi.org/10.1039/c5ob02112j.

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34

Cai, Xiao-hua, Hai-jun Yang, and Guo-lin Zhang. "Aromatization of 1,4-dihydropyridines with selenium dioxide." Canadian Journal of Chemistry 83, no. 3 (March 1, 2005): 273–75. http://dx.doi.org/10.1139/v05-058.

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1,4-Dihydropyridines were aromatized to corresponding pyridines using stoichiometric selenium dioxide at ambient temperature in a yield of 87%~98%.Key words: 1,4-dihydropyridines, aromatization, oxidation, pyridine derivatives, selenium dioxide.

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35

Ghotekar, Bhausaheb K., Muddassar A. Kazi, Madhukar N. Jachak, and Raghunath B. Toche. "Effect of substituents on absorption and fluorescence properties of pyrazolo[3,4-b]pyrrolo[2,3-d]pyridines." Canadian Journal of Chemistry 86, no. 11 (November 1, 2008): 1070–76. http://dx.doi.org/10.1139/v08-155.

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A convenient route was successfully developed for the synthesis of novel heterocycles such as pyrazolo[3,4-b]pyrrolo[2,3-d]pyridines (PPP) from pyrazolo[3,4-b]pyridines in good yield. The PPP derivatives synthesized were further studied for their photophysical properties, and it was observed that absorption and emission λmax changed, owing to the substituent effect at 4 positions. These compounds were obtained from highly reactive starting materials, 5-aminopyrazoles and α-acetyl γ-butyrolactone.Key words: α-acetyl γ-butyrolactone, pyrazolo[3,4-b]pyrrolo[2,3-d] pyridine, absorption, emission, fluorescence.

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36

Grinberga, S., A. Krauze, L. Krasnova, and G. Duburs. "Synthesis of 4-Benzo[1,3]Dioxol-5-Ylthieno-[2,3-b]Pyridines." Latvian Journal of Chemistry 51, no. 1-2 (January 1, 2012): 143–48. http://dx.doi.org/10.2478/v10161-012-0002-2.

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Synthesis of 4-Benzo[1,3]Dioxol-5-Ylthieno-[2,3-b]Pyridines 4,7-Dihydrothieno[2,3-b]pyridine 4 and thieno[2,3-b]pyridine 6 were obtained by Thorpe-Ziegler cyclization. Mn(OAc)3/acetic acid system had been used for oxidation of 1,4-dihydropyridine 3 to pyridine derivative 5. 6-Carbamoylmethylsulfanyl-1,4-dihydropyridine 3 was prepared by al-kylation of piperidinium 1,4-dihydropyridine-2-thiolate 1 with iodoacet-amide.

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37

Zhu, Jingyun, Ziyue Chen, Meng He, Daoxin Wang, Liangsen Li, Junchao Qi, Renyi Shi, and Aiwen Lei. "Metal-free electrochemical C3-sulfonylation of imidazo[1,2-a]pyridines." Organic Chemistry Frontiers 8, no. 14 (2021): 3815–19. http://dx.doi.org/10.1039/d1qo00348h.

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An electrochemical C3-sulfonylation of imidazo[1, 2-a]pyridines with sodium benzenesulfinate has been developed, providing an straightforward protocol towards biologically and synthetically useful 3-(arylsulfonyl)imidazo[1, 2-a]pyridine.

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38

Volkov, Pavel A., Anton A. Telezhkin, Kseniya O. Khrapova, Nina I. Ivanova, Alexander I. Albanov, Nina K. Gusarova, and Boris A. Trofimov. "Metal-free SHN cross-coupling of pyridines with phosphine chalcogenides: polarization/deprotonation/oxidation effects of electron-deficient acetylenes." New Journal of Chemistry 45, no. 14 (2021): 6206–19. http://dx.doi.org/10.1039/d1nj00245g.

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Terminal acylacetylenes act as trimodal auxiliaries in SHN cross-coupling of pyridines with phosphine chalcogenides. The reaction proceeds via phosphorylation of the pyridine 2 position followed by 2 → 4-migration of phosphoryl moieties.

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39

Ma, Dongge, Yan Yan, Hongwei Ji, Chuncheng Chen, and Jincai Zhao. "Photocatalytic activation of pyridine for addition reactions: an unconventional reaction feature between a photo-induced hole and electron on TiO2." Chemical Communications 51, no. 98 (2015): 17451–54. http://dx.doi.org/10.1039/c5cc07123b.

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TiO₂ photocatalysis has the ability to furnish a class of coordinated anti-Markovnikov addition reactions between vinylarenes and pyridines. Such pyridine addition reactions occur through a previously undescribed concerted pathway.

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40

Li, Bin, Nana Shen, Yujie Yang, Xinying Zhang, and Xuesen Fan. "Synthesis of naphtho[1′,2′:4,5]imidazo[1,2-a]pyridines via Rh(iii)-catalyzed C–H functionalization of 2-arylimidazo[1,2-a]pyridines with cyclic 2-diazo-1,3-diketones featuring with a ring opening and reannulation." Organic Chemistry Frontiers 7, no. 7 (2020): 919–25. http://dx.doi.org/10.1039/d0qo00073f.

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An unprecedented synthesis of functionalized naphtho[1′,2′:4,5]imidazo[1,2-a]pyridines via rhodium-catalyzed cascade reactions of 2-arylimidazo[1,2-a]pyridine-3-carbaldehydes with cyclic α-diazo-1,3-diketones is presented.

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41

Yang, Chunxia, Wei Zhao, Zhiguo Cheng, Baomin Luo, and Dongqin Bi. "Catalytic system for pyridine oxidation to N-oxides under mild conditions based on polyoxomolybdate." RSC Advances 5, no. 46 (2015): 36809–12. http://dx.doi.org/10.1039/c5ra05196g.

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A reusable and effective catalytic system has been developed for oxidation of pyridines catalyzed by Keplerate polyoxomolybdate ({Mo₁₃₂}) at room temperature. Pyridine compounds could be oxidized in high yields under mild conditions.

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42

Kona, Sridevi, Rama Suresh Ravi, Manab Chakravarty, and Venkata N. R. Chava. "Phosphine-Free Palladium-Catalyzed Direct C-3 Arylation of 2-Phenylimidazo[1,2-a]pyridine Using Silver(I) Carboxylate." Journal of Chemistry 2013 (2013): 1–7. http://dx.doi.org/10.1155/2013/305934.

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Phosphine-free palladium-catalyzed direct arylation of 2-phenyl-imidazo[1,2-a]pyridine has been developed with the concept of using silver(I) carboxylate. This protocol efficiently catalyzes the C-H arylation of 2-phenyl-imidazo[1,2-a]pyridine with aryl iodides to afford the corresponding 2-phenyl-3-aryl-imidazo[1,2-a]pyridines in moderate to-good yields.

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43

Arnestad, Berit, Jan M. Bakke, Ingrid Hegbom, Eli Ranes, Bente Nielsen, Ruby I. Nielsen, Carl Erik Olsen, et al. "Direct Nitration of Pyridine and Substituted Pyridines." Acta Chemica Scandinavica 50 (1996): 556–57. http://dx.doi.org/10.3891/acta.chem.scand.50-0556.

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44

Abdelrazek, Fathy M., Sobhi M. Gomha, Mohamed E. B. Shaaban, Kamal A. Rabee, Heba N. El-Shemy, Abanoub M. Abdallah, and Peter Metz. "One-Pot Three-Component Synthesis and Molecular Docking of Some Novel 2-Thiazolyl Pyridines as Potent Antimicrobial Agents." Mini-Reviews in Medicinal Chemistry 19, no. 6 (March 7, 2019): 527–38. http://dx.doi.org/10.2174/1389557518666181019124104.

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Background: Thiazoles and pyridines are versatile synthetic scaffolds possessing wide spectrum of biological effects including potential antimicrobial activity. Objective: In the efforts to develop suitable antimicrobia drugs, medicinal chemists have focused on thiazole derivatives. A novel series of 2-thiazolyl pyridines was prepared in a one-pot three-component reaction using 2-bromoacetyl pyridine as a starting precursor. Method: Structure of the synthesized compounds was elucidated by spectral data (FT-IR, 1H NMR, 13C NMR, and mass) and elemental analyses. The prepared compounds were screened for their in vitro antimicrobial activity. Results: The results revealed that compounds 4a,b,e-g and 12 showed promising activity. Molecular docking studies using MOE software were carried out for compounds 4a and 4b which exhibited potent activities indicated by the diameter zones (4a; 3.6, 4.0, 1.2 mm) (4b; 4.2, 3.5, 1.5 mm) and the binding affinities (4a; -5.7731, -5.3576, -4.6844 kcal mol-1) (4b; -5.9356, -2.8250, -5.3628 kcal mol-1) against Candida albicans, Bacillus subtilis and Escherichia coli, respectively. Conclusion: This paper describes a facile and efficient MCR for synthesis of 2-thiazolyl pyridines from reaction of 2-bromoacetyl pyridine with different reagents. There was an agreement between the values of binding affinities and interactions and the data obtained from the practical antimicrobial screening of the tested compounds.

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45

Krutošíková, Alžbeta, and Róbert Sleziak. "Synthesis of 2-Arylfuro[3,2-c]pyridines and Their Derivatives." Collection of Czechoslovak Chemical Communications 61, no. 11 (1996): 1627–36. http://dx.doi.org/10.1135/cccc19961627.

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A series of 2-arylfuro[3,2-c]pyridines was synthesized. 3-(5-Aryl-2-furyl)propenoic acids 1a-1h were converted to the acid azides 2a-2h, which in turn were cyclized to give 2-arylfuro[3,2-c]pyridine-4(5H)-ones 4a-4h by heating in Dowtherm. The pyridones 4a-4f were aromatized with phosphorus oxychloride to the 2-aryl-4-chlorofuro[3,2-c]pyridines 5a-5f, which were reduced with zinc and acetic acid to the title compounds 6a-6f. Reacted with phosphorus(V) sulfide, the pyridones 4a-4f yielded the corresponding thiones 7a-7f.

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46

Grisez, Tom, Nitha Panikkassery Ravi, Mathy Froeyen, Dominique Schols, Luc Van Meervelt, Steven De Jonghe, and Wim Dehaen. "Synthesis of a 3,7-Disubstituted Isothiazolo[4,3-b]pyridine as a Potential Inhibitor of Cyclin G-Associated Kinase." Molecules 29, no. 5 (February 22, 2024): 954. http://dx.doi.org/10.3390/molecules29050954.

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Disubstituted isothiazolo[4,3-b]pyridines are known inhibitors of cyclin G-associated kinase. Since 3-substituted-7-aryl-isothiazolo[4,3-b]pyridines remain elusive, a strategy was established to prepare this chemotype, starting from 2,4-dichloro-3-nitropyridine. Selective C-4 arylation using ligand-free Suzuki-Miyaura coupling and palladium-catalyzed aminocarbonylation functioned as key steps in the synthesis. The 3-N-morpholinyl-7-(3,4-dimethoxyphenyl)-isothiazolo[4,3-b]pyridine was completely devoid of GAK affinity, in contrast to its 3,5- and 3,6-disubstituted congeners. Molecular modeling was applied to rationalize its inactivity as a GAK ligand.

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47

Motevalli, Kourosh, Zahra Yaghoubi, and Roghieh Mirzazadeh. "Microwave-Assisted, One-Pot Three Component Synthesis of 2-PhenylH-imidazo[1,2-α]pyridine." E-Journal of Chemistry 9, no. 3 (2012): 1047–52. http://dx.doi.org/10.1155/2012/198615.

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A novel synthesis of 2-phenylH-imidazio[1,2-α] pyridines is described from a one-pot, three-component reaction between pyridine, guanidine (urea or thiourea) and α-bromoketones under microwave irradiation and solvent-free conditions in excellent yields.

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48

Li, Bin, Nana Shen, Xinying Zhang, and Xuesen Fan. "Synthesis of fused imidazo[1,2-a]pyridines derivatives through cascade C(sp2)–H functionalizations." Organic & Biomolecular Chemistry 17, no. 41 (2019): 9140–50. http://dx.doi.org/10.1039/c9ob01744e.

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An efficient and convenient synthesis of fused imidazo[1,2-a]pyridine derivatives from the cascade reactions of 2-arylimidazo[1,2-a]pyridines with a-diazo carbonyl compounds via Rh(iii)-catalyzed C(sp²)–H functionalization/annulation is presented.

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49

Shen, Yang-Lin, Jun-Ling Jin, Yun-Peng Xie, and Xing Lu. "tert-Butyl thiol and pyridine ligand co-protected 50-nuclei clusters: the effect of pyridines on Ag–SR bonds." Dalton Transactions 49, no. 36 (2020): 12574–80. http://dx.doi.org/10.1039/d0dt02003f.

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The presence of pyridine ligands induces expansion of Ag_N–SR bond lengths compared to that of Ag_O–SR without pyridines, which has been proved to profoundly influence the construction of thiolate–silver(i) compounds.

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50

Bhatt, Keval, Dhara Patel, Mrudangsinh Rathod, Ashish Patel, and Drashti Shah. "Efficient Synthesis and Characterization of 6-substituted-N-p-tolyl-imidazo[1,2- a]pyridine-8-carboxamide: A Promising Scaffold for Drug Development." Current Organic Chemistry 27, no. 22 (December 2023): 1978–84. http://dx.doi.org/10.2174/0113852728269243231206044929.

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Abstract: Imidazo[1,2-a]pyridine is a highly significant fused bicyclic heterocycle widely utilized in medicinal chemistry, and it holds a prominent position as a "drug prejudice" framework because of its extensive applications. Numerous approaches have been documented for the synthesis of imidazo[1,2-a]pyridines, with a particular focus on functionalizing these compounds. In this research, we have presented an effective multi-step synthesis method for producing imidazo[1,2-a]pyridines, achieving impressive yields ranging from 93% to 97%. The synthesized compounds were subjected to thorough characterization using various spectral analysis techniques, including FTIR, 1H NMR, 13C NMR, mass spectrometry, and elemental analysis. Overall, this synthetic strategy possesses desirable features for the synthesis of imidazo[1,2-a]pyridines and their derivatives, including high product purity, accessible starting materials, broad substrate scope, scalability, and transformability. These characteristics make it a promising approach for further development and potential application in the synthesis of valuable therapeutic compounds.

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