Condensed O-, N-heterocycles by the transformation of azidoacrylates

Summary A number of furo[3,2-c]pyridines (4a–4d) and benzo[b]derivative (4e), as well as pyrrolo[2,3-4,5]furo[3,2-c]pyridine (8) were prepared by reaction of the corresponding iminophosphoranes, available from ethyl azidoheteroacrylates and triphenylphosphine, with phenyl isocyanate. The appropriate azidoheteroacrylates were used for the preparation of some substituted furo[3,2-b:4,5-b]dipyrroles (6). The reactions of the prepared compounds are described.

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Kondensierte O-, N-Heterocyclen durch Umwandlung von Azidoacrylaten

Zusammenfassung Eine Anzahl von Furo[3,2-c]pyridinen (4a –4d), ein Benzo[b]derivat (4e) und Pyrrolo[2,3:4,5]furo[3,2-c]pyridin (8) wurden durch die Reaktion von Phenylisocyanaten mit den entsprechenden Iminophosphoranen dargestellt, die aus Ethyl-azidoheteroacrylaten und Triphenylphosphin leicht zugänglich sind. Die entsprechenden Azidoacrylate wurden zur Synthese einiger Furo[3,2-b:4,5-b]dipyrrole (6) verwendet. Die Reaktionen einiger dieser Verbindungen werden beschrieben.

     

A concise synthesis of all four possible benzo[4,5]furopyridines via palladium-mediated reactions

[reaction: see text] By taking advantage of the alpha- and gamma-activation of chloropyridines as well as palladium-mediated reactions, all four possible benzo[4,5]furopyridine tricyclic heterocycles, benzo[4,5]furo[2,3-b]pyridine, benzo[4,5]furo[2,3-c]pyridine, benzo[4,5]furo[3,2-c]pyridine, and benzo[4,5]furo[3,2-b]pyridine, are efficiently synthesized from 2-chloro-3-iodopyridine, 3-chloro-4-stannylpyridine, 4-chloro-3-iodopyridine, and 2-chloro-3-hydroxypyridine, respectively.     

Electrophilic cyclization of o-acetoxy- and o-benzyloxyalkynylpyridines: an easy entry into 2,3-disubstituted furopyridines

[reaction: see text] 2,3-Disubstituted furo[3,2-b]pyridines, 2,3-disubstituted furo[2,3-b]pyridines, and 2,3-disubstituted furo[2,3-c]pyridines are readily prepared under mild conditions via the palladium-catalyzed cross-coupling of 1-alkynes with o-iodoacetoxy- or o-iodobenzyloxypyridines, followed by electrophilic cyclization by I(2) or by PdCl(2) under a balloon of carbon monoxide.     

Furo[3,2‐b]pyridine: A Privileged Scaffold for Highly Selective Kinase Inhibitors and Effective Modulators of the Hedgehog Pathway

Reported is the identification of the furo[3,2‐b]pyridine core as a novel scaffold for potent and highly selective inhibitors of cdc‐like kinases (CLKs) and efficient modulators of the Hedgehog signaling pathway. Initially, a diverse target compound set was prepared by synthetic sequences based on chemoselective metal‐mediated couplings, including assembly of the furo[3,2‐b]pyridine scaffold by copper‐mediated oxidative cyclization. Optimization of the subseries containing 3,5‐disubstituted furo[3,2‐b]pyridines afforded potent, cell‐active, and highly selective inhibitors of CLKs. Profiling of the kinase‐inactive subset of 3,5,7‐trisubstituted furo[3,2‐b]pyridines revealed sub‐micromolar modulators of the Hedgehog pathway.     

First synthesis and further derivatization of furo[3,2-c]pyrazol-6-ones

For the very first time furo[3,2-c]pyrazoles have been prepared starting from pyrazole building blocks instead from furanes. During this synthesis effort two previously unknown heterocyclic scaffolds have been discovered, the furo[3,2-c]pyrazol-6-ones and the 2-cyano-3-aminofuran-4-ones.     

Synthesis of New Furo[2,3-b]pyridine and Furo[3,2-d]pyrimidine Derivatives

Russian Journal of Organic Chemistry - New furo[2,3-b]pyridine and pyrido[3′,2′:4,5]furo[3,2-d]pyrimidine derivatives were synthesized from ethyl...     

Furo[3,2-b]pyridine: a convenient unit for the synthesis of polyheterocycles

An efficient and rapid synthesis of furo[3,2-b]pyridine 1 is described using a one-pot Sonogashira coupling/heteroannulation sequence. Regioselective lithiation of this synthon was performed leading to various 2-substituted furo[3,2-b]pyridines. Some of them were used as substrates for short functional synthesis of polyheterocycles.     

Modified Coumarins. 6. Synthesis of Substituted 5,6-Benzopsoralens

Substituted 5H-benzo[c]furo[3,2-g]chromen-5-ones, modified analogs of psoralen that contain a benzene ring annelated at the 5,6-position of a furo[3,2-g]chromen-7-one system, were synthesized from 3-hydroxy- 6H-benzo[c]chromen-6-ones.     

Furopyridines. XIV. Synthesis of 2-aminoalkyl derivatives of furo[2,3-b]-, furo[3,2-b], furo[2,3-c]- and furo[3,2-c]pyridine

The preparation of 2-aminomethyl- 3a-d , 2-acetamidomethyl- 4a-d , 2-N,N-dimethylaminomethyl- 5a-d , 2-(1-hydroxy-2-nitroethyl)- 6a-d , 2-(1-hydroxyl-2-aminoethyl)- 7a-d and 2-(1-hydroxy-2-N,N-dimethylaminoethyl)- 8b-d derivatives of furo[2,3-b]-, furo[3,2-b]-, furo[2,3-c]- and furo[3,2-c]pyridine is described.     

Synthesis of furo[3,2-c]- and pyrano[3,2-c]quinolines by lanthanide triflate catalyzed imino-Diels-Alder reaction

Imino Diels-Alder reaction of imines with 2,3-dihydrofuran or 3,4-dihydro-2H-pyran proceeded smoothly in the presence of a catalytic amount (0.5 mol %) of ytterbium triflate to afford furo[3,2-c]- and pyrano[3,2-c] quinolines conveniently in high yield.     

Synthesis of substituted furo[3,2-e][1,2,4]triazolo[4,3-c]pyrimidines and furo[3,2-e]tetrazolo[1,5-c]pyrimidines

A series of substituted furo[3,2-e][1,2,4]triazolo[4,3-c]pyrimidines and furo[3,2-e]tetrazolo[1,5-c]pyrimidines were obtained from reactions of substituted 2-dimemylamino-4-hydrazmofuro[2,3-d]pyrimidines with orthoesters or sodium nitrite in acetic acid, respectively.     

Heteroyohimbane a noyau furannique. Nouvelle voie d'acces aux derives de la furo[3,2-c]pyrone et de la furo[3,2-c]pyridine

3,4-Dicarbomethoxyfuran bearing an acetonyl or a phenacy group in the 2 position w3as prepared by pyrolysis of the dihydrocyclo adduct from methyl acetylendicarboxylate and 2-acetonyl- or 2-phenacylfuran. Condensation of 2-acetonyl-3,4-dicarbomethoxyfuran with tryptamine gave a new heteroyohimbane with a furan ring, indolo[2,3-a]furo[3,2-c]quinolizine, a potential precursor of yohimbane. Ketodiacids from saponification allow one to obtain derivatives of the following heterocyclic ring systems, namely 4H-furo[3,2-c]pyran-4-one and furo[3,2-c]pyridine.     

Preparation of Furo[3,2‐c]coumarins from 3‐Cinnamoyl‐4‐hydroxy‐2H‐chromen‐2‐ones and Acyl Chlorides: A Bu3P‐Mediated C‐Acylation/Cyclization Sequence

A Bu₃P‐mediated cyclization reaction of 3‐cinnamoyl‐4‐hydroxy‐2H‐chromen‐2‐ones though electrophilic addition of acyl chlorides towards the synthesis of highly functionalized furo[3,2‐c]coumarins bearing a phosphorus ylide moiety is described. These unprecedented cyclization reaction proceeds under mild reaction conditions within short reaction times (1 min to 1 h), and can be further applied in the synthesis of alkenyl‐substituted furo[3,2‐c]coumarins by the treatment with carbonyl electrophiles under basic conditions.     

Synthesis of furo[3,2-c]coumarins via I2/TBHP-mediated reaction of 4-hydroxycoumarins with terminal alkynes

An efficient I₂/TBHP-mediated process for the formation of furo[3,2-c]coumarins from readily available materials has been developed. This process for the formation of furo[3,2-c]coumarins is quite environmental friendly and atom-economical.     

Two efficient cascade reactions to synthesize substituted furocoumarins

We have developed two efficient one-pot reactions to generate furo[3,2-c]coumarins and chlorofuro[3,2-c]coumarins through addition/cyclization/oxidation and chlorination. One cascade addition/cyclization/oxidation sequence of 1 with H(2)O in the presence of 20% CuCl as Lewis acid under an air atmosphere generated the 2-substituted-4 H-furo[3,2-c]chromen-4-one 2. Another sequence in the presence of 10% CuBr and excess CuCl(2) as the oxidant afforded the 3-chloro-2-substituted-4 H-furo[3,2- c]chromen-4-one 3.     

Polycyclic N‐Heterocyclic Compounds,Part 69: Synthesis of 5‐amino‐1,2‐dihydro[1]benzofuro[3,2‐d]furo[2,3‐b]pyridines and their transformations to related compounds

Reaction of 3‐(3‐cyanopropoxy)[1]benzofuran‐2‐carbonitriles with potassium tert‐butoxide gave 5‐amino‐1,2‐dihydro[1]benzofuro[3,2‐d]furo[2,3‐b]pyridines and 5‐amino‐2,3‐dihydro[1]benzofuro[3,2‐b]oxepin‐4‐carbonitriles as new ring systems. Reactions of the 5‐chloro derivative, obtained from 5‐amino‐1,2‐dihydro[1]benzofuro[3,2‐d]furo[2,3‐b]pyridine, produced a dihydrofuran ring‐opened compound and 5‐substituted compounds. J. Heterocyclic Chem.,(2011).     

Furopyridines. XI. 13C NMR Spectra of 2- or 3-Substituted Furo[2,3-b]-, Furo[3,2-b]-, Furo[2,3-c]- and Furo[3,2-c]pyridine

The ¹³C nmr spectra of 2- or 3-monosubstituted furo[2,3-b]- 1a-1j , furo[3,2-b]- 2a-2j , furo[2,3-c]- 3a-3j and furo[3,2-c]pyridine derivatives 4a-4j are reported. Effects by change in annelation and substituent effects on ¹³C chemical shifts and carbon-proton coupling constants are discussed. The spectra of benzo[b]furan derivatives 5a-5j having the corresponding substituent are also reported for comparison.     

Indazolequinones in the Nenitzescu Reaction. Synthesis of Pyrrolo[2,3-e]- and Furo[2,3-e]indazoles

A heterocyclic quinone was used in the Nenitzescu reaction for the first time. New tricyclic compounds - pyrrolo[3,2-e]- and furo[3,2-e]indazoles - were synthesized by the condensation of 1,3-diphenyl-4,7-dioxoindazole with various enamines.     

Synthesis of derivatives of pyrido[3′,2′:4,5]furo[3,2-c]isoquinoline heterocyclic system

An approach to the synthesis of derivatives of new heterocyclic system, pyrido[3′,2′:4,5]-furo[3,2-c]isoquinoline, was suggested. A condensation reaction of substituted 3-cyanopyridin-2(1H)-ones with methyl 2-(chloromethyl)benzoate and subsequent treatment of the condensation product with potassium tert-butoxide leads to substituted pyrido[3′,2′:4,5]furo[3,2-c]-isoquinolin-5(6H)-ones. Similarly, a condensation reaction of substituted 3-cyanopyridin-2(1H)-ones with 2-(chloromethyl)benzonitrile and subsequent treatment of the condensation product with potassium tert-butoxide gives substituted 5-aminopyrido[3′,2′:4,5]furo[3,2-c]-isoquinolines.     

Nouvelle méthode d'accès aux benzo[h]furo[3,2-c]quinoléines,analogues isostériques des benzo[c]phénanthridines

A convenient synthesis of the benzo[h]furo[3,2-c]quinoline ring is reported. Hydrogenation of dienic adducts 5 gives comppounds 6. Successive pyrolysis and alcaline hydrolysis of 6 provide diacids 9 which in the presence of anhydrous ammonium acetate and acetic acid undergoes intramolecular cyclisation to give benzo[h]furo[3,2-c]quinolone derivatives 12. The modulation of the 7-carboxy group and introduction of amino groups in the 6 position are then realized.