Ein neuer zugang zu indeno[1,2-b]pyridinen

A new synthesis of 5H-indeno[1,2-6]pyridines [IV] starting from 4-cyanobutyrophenones [I] or their cyclization products, the 6-phenyl-3,4-dihydropyridin-2-ones [II], is reported. The condensation of I or II in polyphosphoric acid with aromatic or heteroaromatic aldehydes [III] yields 1,2,3,4-tetrahydro-5H-indeno[1,2-b]pyridin-2-ones [IV]. 2,3,4,4a,5,9b-Hexahydro-1H-indeno[1,2-b]pyridines [X, XI] which were previously difficult to obtain can now be easily synthesized from compounds IV.     

Synthesis of isoquinolines and heterocycle-fused pyridines via three-component cascade reaction of aryl ketones, hydroxylamine, and alkynes

An efficient one-pot synthesis of isoquinolines and heterocycle-fused pyridines by three-component reaction of aryl ketones, hydroxylamine, and alkynes is developed. The reaction involves condensation of aryl ketones and hydroxylamine, rhodium(III)-catalyzed C-H bond activation of the in situ generated aryl ketone oximes, and cyclization with internal alkynes. This protocol enables rapid assembly of multisubstituted isoquinolines as well as γ-carbolines, furo[2,3-c]pyridines, thieno[2,3-c]pyridines, and benzofuro[2,3-c]pyridines from readily available substrates.     

Reactions of nucleophilic substitution of 4-aryl-5-carbomethoxy-6-methyl-2-chloro-3-cyanopyridines

Methods of synthesis of 5-carbomethoxy-substituted pyrazolo[3,4-b]pyridines and 3H-imidazo[4,5-b]pyridines by their reaction with hydrazine hydrate or as a result of Hofmann rearrangement of the corresponding 2-aminopyridines were developed based on 4-aryl-3-carbamoyl(or cyano)-5-carbomethoxy-6-methyl-2-chloropyridines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No.12, pp. 1646–1650, December 1992.     

Synthesis of 3-amino derivatives of benzo[b]furo[2,3-c]pyridines

The reaction of 1,7-dimethyl-3(2H)-benzo[b]furo[2,3-c]pyridone with phosphoric acid amides gave 1,7-dimethyl-3-dimethylamino (morpholino)benzo[b]furo[2,3-c]pyridines. A method for the synthesis of 3-amino derivatives of 4-nitrobenzo[b]furo[2,3-c]pyridines, which consists in heating 1,7-dimethyl-4-nitro-3(2H)-benzo[b]furo[2,3-c]pyridone with hexamethyldisilazane and secondary or primary amines in pyridine, was developed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1552–1555, November, 1991.     

Ein biologischer Vergleich zwischen Benzol und Pyridin in kondensierten Ringsystemen

The synthesis of imidazo[4,5-b]pyridines and of [1,2,4]-triazolo[1,5-a]pyridines is described, and their biological activity in relation to the standard antiviral substance, 2-(α-hydroxybenzyl)benzimidazol, is discussed.     

Triazolopyridines. Part 26: The preparation of novel [1,2,3]triazolo[1,5-a]pyridine sulfoxides

The regioselective synthesis of new triazolopyridine halides and sulfoxides with the substituent in all different ring positions of [1,2,3]triazolo[1,5-a]pyridines is presented. The triazolo ring opening reaction of some representative sulfoxides to obtain disubstituted pyridines is also studied.     

One-pot synthesis of imidazo[1,2-a]pyridines from benzyl halides or benzyl tosylates, 2-aminopyridines and isocyanides

A one-pot synthesis of imidazo[1,2-a]pyridines is described. Benzyl halides or benzyl tosylates are oxidized to aldehydes under mild Kornblum conditions which then undergo a three-component reaction with various 2-aminopyridines and isocyanides to afford the imidazo[1,2-a]pyridines in excellent yields.     

Triazolopyridines. Part 24: New polynitrogenated potential helicating ligands

The synthesis of novel 7-{[1,2,3]triazolo[1,5-a]pyridin-3-yl}-[1,2,3]triazolo[1,5-a]pyridines 7, 2-pyridyl-[1,2,3]triazolo[1,5-a]pyrid-7-ylmethanols 11, 3-(6-substituted-2-pyridyl)-[1,2,3]triazolo[1,5-a]pyridines 12, and 7,7′-disubstituted-3,3′-[1,2,3]triazolo[1,5-a]pyridine 20, interesting polynitrogenated ligands as potential helicating compounds or luminescent sensors, from [1,2,3]triazolo[1,5-a]pyridines is described.     

Cu(I)-catalyzed synthesis of imidazo[1,2-a]pyridines from aminopyridines and nitroolefins using air as the oxidant

A copper-catalyzed method for the synthesis of imidazo[1,2-a]pyridines with aminopyridines and nitroolefins using air as oxidation agent in a one-pot procedure has been developed. In this process, the reaction appears to be very general and suitable for construction of a variety of imidazo[1,2-a]pyridines.     

Imidazo [4,5-c] - and [4,5-6] pyridines

The synthesis of novel imidazo[4,5-c]pyridines 11-13 and imidazo[4,5-b]pyridines 18-20 is described using 2 as the starting material. The synthesis is generally applicable for the introduction of a wide variety of substituents.     

Aza and deaza analogs of purine nucleosides (review)

Methods for the preparation of aza and deaza analogs of purine nucleosides, viz., nucleosides of imidazo[4,5-d]-v-triazines, imidazo[4,5-b]pyridines, and imidazo[4,5-c]pyridines, and their properties are described. References to the synthesis of nucleosides of imidazo[4,5-d]pyridazines, imidazo[4,5-c]pyridazines, and imidazo[4,5-b]pyrazines are also given.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 147–161, February, 1981.     

A novel preparation of thiazolo[5,4-c]pyridines and the synthesis of some imidazo[4,5-c]pyridines and oxazolo[4,5-c]pyridines

Diethoxymethyl acetate was used to cyclize o-disubstituted aminopyridines to oxazolo[4,5-c]pyridines and imidazo[4,5-c]pyridines. All the possible imidazole-methylated imidazo[4,5-c]pyridines were prepared. A novel synthesis of 2-substituted thiazolo[5,4-c]pyridines and 4-amino-3-pyridinethiol was discovered.     

Synthesis of Imidazo[1,2‐a]pyridines: C‐H Functionalization in the Direction of C‐S Bond Formation

Imidazo[1,2‐a]pyridines play an important role in medicinal chemistry. In spite of very drastic developments on syntheses and functionalization in this area, the use of inexpensive catalysts and mild reaction conditions constitutes an important role in pharmaceutical applications. This account describes our recent efforts on the development of new methods for the synthesis of imidazo[1,2‐a]pyridines using readily available starting substrates and catalysts under very mild reaction conditions. In the direction of enhancement of biological activity, we also described the synthesis of functionalized imidazo [1,2‐a]pyridine derivatives.     

Terminal Alkynes as One-Carbon Donors in [5+1] Heteroannulation: Synthesis of Pyridines via Ynimine Intermediates and Application in the Total Synthesis of Anibamine B

Transition-metal-catalyzed [4+2] heteroannulation of α,β-unsaturated oximes and their derivatives with alkynes has been developed into a powerful strategy for the synthesis of pyridines. It nevertheless lacks regioselectivity when unsymmetrically substituted alkynes are used. We report herein the unprecedented synthesis of polysubstituted pyridines by a formal [5+1] heteroannulation of two readily accessible building blocks. A copper-catalyzed aza-Sonogashira cross-coupling between β,γ-unsaturated oxime esters and terminal alkynes affords ynimines, which, without isolation, undergo an acid-catalyzed domino reaction involving ketenimine formation, 6π-electrocyclization and aromatization to afford pyridines. Terminal alkynes served as a one-carbon donor to the pyridine core in this transformation. Di- through pentasubstituted pyridines are accessible with complete regioselectivity and excellent functional-group compatibility. The first total synthesis of anibamine B, an indolizinium alkaloid with potent antiplasmodial activity, was accomplished featuring this reaction as a key step.     

Synthesis of polysubstituted 4,5,6,7-tetrahydrofuro[2,3-c]pyridines by a novel multicomponent reaction

[reaction: see text] A novel three-component synthesis of tetrahydrofuro[2,3-c]pyridines from readily accessible starting materials is described. Simply heating a toluene solution of an aminopentynoate, an aldehyde, and an alpha-isocyanoacetamide in the presence of ammonium chloride provided the 4,5,6,7-tetrahydrofuro[2,3-c]pyridines in good to excellent yield. The fused ring system is produced in this one-pot process by the concomitant formation of five chemical bonds.     

Multicomponent synthesis of imidazo[1,2-a]pyridines using catalytic zinc chloride

The novel use of zinc chloride to catalyze the one-pot, three component synthesis of imidazo[1,2-a]pyridines from a range of substrates using either conventional heating or microwave irradiation is described. This methodology affords a number of imidazo[1,2-a]pyridines in reasonable yields and short reaction times without any significant optimization of the reaction conditions.     

Synthesis of 3-aryl-6H-isoxazolo[3,4-d]pyrazolo[3,4-b]pyridines and 3-aryl-6H-isoxazolo[5,4-d]pyrazolo[3,4-b]pyridines

The synthesis and characterization of a number of 3-aryl-6H-isoxazolo[3,4-d]pyrazolo[3,4-b]pyridines and 3-aryl-6H-isoxazolo[5,4-d]pyrazolo[3,4–6]pyridines from common precursors, 5-benzoyl-4-chloro-1H-pyrazolo-[3,4-b]pyridines, has been described. The structures were determined by unambiguous chemical synthesis and by isolation and ¹³C nmr analysis of some key, isolated, intermediates. The ability of these compounds to displace [3H]flunitrazepam from CNS binding sites was also observed.     

Anomeric Stereoauxiliary Cleavage of the C−N Bond of d-Glucosamine for the Preparation of Imidazo[1,5-a]pyridines

The targeted cleavage of the C−N bonds of alkyl primary amines in sustainable compounds of biomass according to a metal-free pathway and the conjunction of nitrogen in the synthesis of imidazo[1,5-a]pyridines are still highly challenging. Despite tremendous progress in the synthesis of imidazo[1,5-a]pyridines over the past decade, many of them can still not be efficiently prepared. Herein, we report an anomeric stereoauxiliary approach for the synthesis of a wide range of imidazo[1,5-a]pyridines after cleaving the C−N bond of d -glucosamine (α-2° amine) from biobased resources. This new approach expands the scope of readily accessible imidazo[1,5-a]pyridines relative to existing state-of-the-art methods. A key strategic advantage of this approach is that the α-anomer of d -glucosamine enables C−N bond cleavage via a seven-membered ring transition state. By using this novel method, a series of imidazo[1,5-a]pyridine derivatives (>80 examples) was synthesized from pyridine ketones (including para-dipyridine ketone) and aldehydes (including para-dialdehyde). Imidazo[1,5-a]pyridine derivatives containing diverse important deuterated C(sp²)−H and C(sp³)−H bonds were also efficiently achieved.     

Ruthenium-catalyzed cycloisomerization-6pi-cyclization: a novel route to pyridines

[reaction: see text] Herein we report a method for the synthesis of substituted pyridines. The unsaturated ketones and aldehydes derived from the cycloisomerization of primary and secondary propargyl diynols in the presence of [CpRu(CH3CN)3]PF6 (1) are converted to 1-azatrienes which in turn undergo a subsequent electrocyclization-dehydration to provide pyridines with excellent regiocontrol.     

Synthesis of novel condensed pyridines and pyrido[2,3-<Emphasis Type="Italic">d</Emphasis>]pyrimidines

Methods have been developed for the synthesis of novel derivatives of pyrano[3,4-c]pyridines, 2,7-naphthyridines, and condensed pyrido[2,3-d]pyrimidines by condensation of thiopyranthiones.