A convenient route to functionalized 3-amino-N-methylfuro[3,2-b]pyridine-2-carboxamides

The synthesis of novel functionalized 3-amino-N-methylfuro[3,2-b]pyridine-2-carboxamides is described from cyanopyridine intermediates. Based on the difference in halogen reactivity, ethyl [(5-bromo-2-chloropyridin-3-yl)oxy]acetate was functionalized by a palladium-catalyzed reaction, before the cyclization to the desired furo[3,2-b]pyridines.     

Intramolecular 4+2 cycloaddition of thieno[2,3-e][1,2,4]triazines: routes towards condensed thieno[2,3-b]pyridines

Synthetic approaches towards new condensed thienopyridine ring systems including furo[2,3-b]thieno[3,2-e]pyridines, bisthieno[2,3-b:3′,2′-e]pyridines, 5H-chromeno[2,3-b]thieno[3,2-e]pyridines, 5H-benzo(f)chromeno[2,3-b]thieno[3,2-e]pyridines have been achieved by application of intramolecular 4+2 cycloaddition reactions of suitably designed thieno[2,3-e][1,2,4]triazines tethered with alkene or alkyne terminals.     

A novel multicomponent reaction to synthesize substituted furo[3,2-c]chromenes via a Pd-catalyzed cascade process

A novel one-pot three-component reaction for the synthesis of multisubstituted furo[3,2-c]chromenes using 3-(1-alkynyl)chromones, aryl iodides, and alcohols is developed via Pd-catalyzed cascade 1,4-addition and cyclization. This synthetic approach efficiently generates two C-O bonds and one C-C bond to construct diverse furo[3,2-c]chromenes structures.     

Synthesis of a novel tricyclic 1,6,7,8-tetrahydro-2H-cyclopenta[b]furo[3,2-d]pyridine derivative,the 5-aza analog of ramelteon

The 5-aza analog of ramelteon 3, a novel tricyclic 1,6,7,8-tetrahydro-2H-cyclopenta[b]furo[3,2-d]pyridine derivative, was synthesized by hetero-Diels–Alder reaction and chemoselective Dieckmann condensation.     

Furopyridines. III. A new synthesis of furo[3,2-b]pyridine

A convenient synthesis of furo[3,2-b]pyridine and its 2- and 3-methyl derivatives from ethyl 3-hydroxypiconate ( 1 ) is described. The hydroxy ester 1 was O-alkylated with ethyl bromoacetate or ethyl 2-bromopropionate to give the diester 2a or 2b . Cyclization of compound 2a afforded ethyl 3-hydroxyfuro[3,2-b]pyridine-2-carboxylate ( 3 ) which in turn was hydrolyzed and decarboxylated to give furo[3,2-b]pyridin-3-(2H)-one ( 4a ). Cyclization of 2b gave the 2-methyl derivative 4b . Reduction of 4a and 4b with sodium borohydride yielded the corresponding hydroxy derivative 5a and 5b respectively, which were dehydrated with phosphoric acid to give furo[3,2-b]pyridine ( 6a ) and its 2-methyl derivative ( 6b ). 2-Acetylpyridin-3-ol ( 8 ) was converted to the ethoxycarbonylmethyl ether ( 9 ) by O-alkylation with ethyl bromoacetate, which was cyclized to give 3-methylfuro[3,2-b]pyridine-2-carboxylic acid ( 10 ). Decarboxylation of 10 afforded 3-methylfuro[3,2-b]pyridine ( 11 ).     

Palladium-catalyzed reductive N-heterocyclization of alkenyl-substituted nitroarenes as a viable method for the preparation of bicyclic pyrrolo-fused heteroaromatic compounds

Palladium-catalyzed, carbon monoxide-mediated reductive N-heterocyclization of nitro-heteroaromatic compounds having an alkene adjacent to the nitro-group affords bicyclic pyrrolo-fused heteroaromatic molecules. This type of reaction was used to prepare the fused bicyclo[3.3.0] ring-system: thieno[3,2-b]pyrrole, thieno[2,3-b]pyrrole, furo[2,3-b]pyrrole, pyrrolo[3,2-d]thiazole, and pyrrolo[2,3-d]imidazole and the bicyclo[4.3.0] ring-systems: pyrrolo[3,2-b]pyridine, pyrrolo[2,3-b]pyridine, pyrrolo[3,2-c]pyridine, pyrrolo[2,3-c]pyridine, pyrrolo[3,2-c]pyridazine, and pyrrolo[3,2-d]pyrimidine in 32-94% yield.     

Copper-catalyzed radical/radical cross-coupling of ketoxime carboxylates with 4-hydroxycoumarins: A novel synthesis of furo[3,2-c]-coumarins

A novel and efficient strategy for the synthesis of furo[3,2-c]coumarins has been developed via copper-catalyzed radical/radical cross-coupling of ketoxime carboxylates with 4-hydroxycoumarins. This redox-neutral reaction allows smooth and selective synthesis of 2-substituted, 3-substituted, 2,3-disubstituted and 2,3-fused polycyclic furo[3,2-c]coumarins.     

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.     

Reactions of 1,5-π-cyclization of gem-difluoro-substituted azomethine ylides involving an aromatic ring

Reactions of N-(5-R-furan-2-ylmethylidene)anilines with difluorocarbene proceeds through intermediate azomethine ylides suffering 1,5-π-cyclization to yield 6,6-difluorocyclopropa[b]furo[2,3-c]pyrrole and/or 4,4,6,6-tetrafluorocyclopropa[b]furo[2,3-c]pyrrole. The heating of these compounds without solvent resulted in high yields of 2,5-disubstituted 7-fluoro-4,5-dihydrofuro[3,2-c]pyridin-4(5H)-ones.     

Indole esters as heterocyclic synthons. III. Preparation and reactions of furo[3,2-b]indoles

The preparation of furo[3,2-b]indoles via Dieckmann cyclization is described. The precursor diesters were obtained from 3-hydroxy-1H-indole-2-carboxylic acid esters and methyl or ethyl bromoacetate. Reactions of the furo[3,2-b]indole enolic esters prepared are discussed.     

Convenient synthesis of fused pyrano[3,2-h]- and furo[3,2-h]benzo[f]coumarins from naphthalene-2,3-diol

The treatment of 8-propargyloxy-benzo[f]coumarin with boron trifluoride diethyl etherate in N,N-dimethylformamide under reflux or MW irradiation resulted in pyrano[3,2-h]benzo[f]coumarin, while the furo[3,2-h]benzo[f]coumarin is received from the treatment with N-methylformamide under MW irradiation.     

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.     

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 novel heterocycles from 2-amino-3-cyanomethyl-sulfonyl-4,5-dimethylfuran

The synthesis and selected reactions of the versatile heterocycle 2-amino-3-cyanomethylsulfonyl-4,5-dimethylfuran is reported. In particular, cyclization reaction of the aminofuran yielded a number of novel furo[3,2-b]thiazine 1,1-dioxides. Additionally, a novel tetracyclic system, namely a pyrrolo[2′,3′:5,6]-[1,4]thiazino[3,2-b]quinoline 4,4-dioxide, is prepared via an intramolecular triple-cyclization in which the furan ring is opened and reclosed as a pyrrole.     

A convenient route to functionalized 3-amino-6-bromofuro[3,2-b]pyridine-2-carboxamides

An efficient synthesis of 3-amino-6-bromofuro[3,2-b]pyridine-2-carboxamides is described via the formation of 3-amino-6-bromofuro[3,2-b]pyridine-2-carbonitrile. Functionalization of the amino group at position 3 of the heterocycle will be discussed.     

2-Benzyliden-2H-thieto[3,2-b]quinoline: a new heterocycle and its rearrangement to 2-phenylthieno[3,2-b]quinoline

Synthesis of the strained 2H-thieto[3,2-b]quinoline ring system is reported for the first time. Treatment of (Z)-2-benzyliden-2H-thieto[3,2-b]quinoline derivatives of this heterocycle with base, at reflux in ethanol, causes a novel rearrangement to 2-phenylthieno[3,2-b]quinolines. Indeed, the one-pot reaction of 2-aminobenzaldehydes and (Z)-2-benzylidenethietan-3-one in refluxing basic ethanol leads directly to 2-phenylthieno[3,2-b]quinolines in good yields.     

Intramolecular cyclisation of functionalised heteroaryllithiums. Synthesis of novel indolizinone-based compounds

The intramolecular cyclisation of heteroaryllithiums derived from N-heteroarylmethylpyrrole-2-carboxamides takes place smoothly at low temperature when N-methoxy-N-methyl and morpholine amides are used as internal electrophiles. Halogen-lithium exchange using n-BuLi is the method of choice to achieve metalation on the quinoline and pyridine derivatives, while directed lithiation (LDA) works better for furan. In the case of thiophene both methodologies can be applied. These metalation-cyclisation sequences provide a useful entry to several types of indolizidine based compounds (pyrrolo[1,2-b]acridinones, pyrrolo[1,2-g]quinolones, thieno and furo[3,2-f]indolizinones).     

I2-catalyzed one-pot synthesis of benzofuro/thieno[2,3-b]pyrrole motifs

A novel I₂-catalyzed one-pot multicomponent protocol for the synthesis of a variety of elusive furo[2,3-b]pyrrole and thieno[2,3-b]pyrrole libraries has been established. To date, cyclization among alkanone, hydrazine and 2-bromobenzofuran or 2-bromobenzo[b]thiophene has not been explored in one-pot. Thus, the proposed single step protocol provides a versatile alternative to existing routes for accessing useful furo[2,3-b]pyrrole and thieno[2,3-b]pyrrole libraries.     

Synthesis and alkylation of indolo[3,2-b]carbazoles

Double Fischer cyclisation was used to prepare indolo[3,2-b]carbazole and its 2,8-di-OMe, OH, Br and F-derivatives. N-monosubstituted derivatives of indolo[3,2-b]carbazole (methyl, hydroxymethyl, dimethylaminoethyl) were obtained starting from 5,11-di-Boc-indolo[3,2-b]carbazole.     

Copper-catalyzed intramolecular C–N bond formation reaction of 3-amino-2-(2-bromophenyl)dihydroquinazolinones: synthesis of indazolo[3,2-b]quinazolinones

A copper-catalyzed intramolecular C–N bond formation reaction of 3-amino-2-(2-bromophenyl)dihydroquinazolinones has been developed for the synthesis of indazolo[3,2-b]quinazolinones in moderate to good yields. The structure of the newly synthesized indazolo[3,2-b]quinazolinones was unambiguously confirmed by X-ray single-crystal diffraction analysis. Moreover, a possible mechanism for the formation of indazolo[3,2-b]quinazolinones is discussed.