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 ).     

Furopyridines. XX. Wittig-horner reaction of a phosphonate of reissert analogues of furo[3,2-c]-, -[2,3-c]- and -[3,2-b]pyridines

Furo[3,2-c]-( 1a ), -[2,3-c]- ( 1b ) and -[3,2-b]pyridine ( 1c ) were reacted with isopropyl chloroformate and trimethyl phosphite to give dimethyl 5-isopropoxycarbonyl-4,5-dihydrofuro[3,2-c]pyridine-4-phosphonate ( 2a ), dimethyl 6-isopropoxycarbonyl-6,7-dihydrofuro[2,3-c]pyridine-7-phosphonate ( 2b ) and dimethyl 4-isopropoxycarbonyl-4,7-dihydrofuro[3,2-b]pyridine-7-phosphonate ( 2c ) as unstable syrups. Reaction of 2b and 2c with n-butyllithium and then with benzaldehyde, p-methoxybenzaldehyde, p-cyanobenzalde-hyde or propionaldehyde afforded the normal Wittig reaction products 5b-H, 5b-OMe, 5b-CN, 5b-Et, 5c-H, 5c-H, 5c-OMe and 5c-CN , except for 2b with propionaldehyde. While, the same reactions of compound 2a and the reaction of 2b with propionaldehyde afforded the unexpected products, 5-isopropoxycar-bonylfuro[3,2-c]pyridinio-4-aryl-(or ethyl)methoxides 3a-H, 3a-OMe, 3a-CN and 3a-Et , 4-(1′-aryl(or ethyl)-1′-hydroxymethyl)furo[3,2-c]pyridines 4a-H, 4a-OMe, 4a-CN and 4a-Et accompanying formation of the normal products. Treatment of the normal Wittig reaction products with lithium diisopropylamide and then with acetone gave the derivatives alkylated at the 2-or the benzylic positions.     

Furopyridines. XIII. Reaction of 2-methylfuro[2,3-b]-, -[3,2-b]-, -[2,3-c]- and -[3,2-c]pyridines with lithium diisopropylamide

Lithiation of 2-methylfuro[2,3-b]- 1a , -[2,3-c]- 1c and -[3,2-c]pyridine 1d with lithium diisopropylamide at ?75° and subsequent treatment with deuterium chloride in deuterium oxide afforded 2-monodeuteriomethyl compounds 2a, 2c and 2d , while 2-methylfuro[3,2-b]pyridine 1b gave a mixture of 1b, 2b , 2-methyl-3-deuteriofuro[3,2-b]pyridine 2′b and 2-(1-proynyl)pyridin-3-ol 5 . The same reaction of 1a at ?40° gave 3-(1,2-propadienyl)pyridin-2-ol 3 and 3-(2-propynyl)pyridin-2-ol 4 . Reaction of the lithio intermediates from 1a, 1c and 1d with benzaldehyde, propionaldehyde and acetone afforded the corresponding alcohol derivatives 6a, 6c, 6d, 7a, 7c, 7d, 8a, 8c and 8d in excellent yield; while the reaction of lithio intermediate from 1b gave the expected alcohols 6b and 8b in lower yields accompanied by formation of 3-alkylated compounds 9, 11, 12 and compound 5 . While reaction of the intermediates from 1a, 1b and 1d with N,N-dimethylacetamide yielded the 2-acetonyl compounds 13a, 13b and 13d in good yield, the same reaction of 1c did not give any acetylated product but recovery of the starting compound almost quantitatively.     

Furopyridines. VI. Preparation and reactions of 2- and 3-substituted furo[2,3-b]pyridines

This paper describes the synthesis and chemical properties of some 2- and 3-substituted furo[2,3-b]pyridines. Reaction of ethyl 2-chloronicotinate 1 with sodium ethoxycarbonylmethoxide or 1-ethoxycarbonyl-1-ethoxide gave β-keto ester 2 or ketone 5 , respectively. Ketonic hydrolysis of 2 afforded ketone 3, from which furo[2,3-b]pyridine 4 was obtained by the method of Sliwa. While, 2-methyl derivative 7 was prepared from 5 by reduction, O-acetylation and the subsequent pyrolysis. Reaction of ketone 3 with methyllithium gave tertiary alcohol 8 which was O-acetylated and pyrolyzed to give 3-methyl derivative 9 . Formylation of 4 , via lithio intermediate, with DMF yielded 2-formyl derivative 10 , from which 7 , was obtained by Wolff-Kishner reduction. Dehydration of the oxime 11 of 10 gave 2-cyano derivative 12 , which was hydrolyzed to give 2-carboxylic acid 13 . Reaction of 3-bromo compound 14 with copper(I) cyanide gave 3-cyano derivative 15 . Alkaline hydrolysis of 15 afforded compound 16 and 17 , while acidic hydrolysis gave carboxamide 18 . Reduction of 15 with DIBAL-H afforded 3-formyl derivative 19 . Wolff-Kishner reduction of 19 gave no reduction product 9 but hydrazone 20 . Reduction of tosylhydrazone 21 with sodium borohydride in methanol afforded 3-methoxymethylfuro[2,3-b]pyridine 22 .     

Chemistry of benzo[b]furan. V.. Synthesis of substituted thia-analogs and oxa-analogs of dihydrorutecarpine and evodiamine

Cycloaddition of 3,4-dihydrobenzo[b]thieno[2,3-c]pyridine ( 6 ) with the sulfinamide anhydride 9 (R = H) afforded the thia-analog of dihydrorutecarpine ( 2a ). Condensation of the imine 6 with the sulfinamide anhydride 9 (R = CH₃) gave the thia-analog of evodiamine ( 2b ). Starting from 1-methyl-3,4-dihydrobenzo[b]thieno[2,3-c]pyridine ( 12 ) and 1-methyl-3,4-dihydrobenzo[b]furo[2,3-c]pyridine ( 14 ), a series of 3-methyl derivatives of thia-analogs of dihydrorutecarpine and evodiamine ( 2c-2i ) and oxa-analogs of dihydrorutecarpine and evodiamine ( 1a-1g ) were similarly prepared.     

Furopyridines. XXI. Synthesis of cyano derivatives of furo-[2,3-b]-, -[2,3-c]- and -[3,2-c]pyridine and their conversion to derivatives having another carbon-substituent

Cyanation of furo[2,3-b]-, -[2,3-c]- and -[3,2-c]pyridine N-oxides 1a, 1b and 1c by the Reissert-Henze method, reaction with benzoyl chloride and trimethylsilyl cyanide in dichloromethane and the reaction with trimethylsilyl cyanide and triethylamine in acetonitrile afforded 6-cyanofuro[2,3-b]- 2a , 7-cyanofuro[2,3-c]- 2b and 4-cyanofuro[3,2-c]pyridine 2c in moderate to excellent yield. The cyano group in 2a, 2b and 2c was converted to carboxamides 3a, 3b and 3c , ethyl imidates 5a, 5b and 5c and ethyl carboxylates 6a, 6b and 6c . Reaction of the N-oxides with trimethylsily bromide in acetonitrile gave the deoxygenated furopyridine 7a and 7d , bifuropyridyl 8b and 8c , and the N-oxide 9 of 8c .     

Furannes et pyrroles disubstitués en 2,3. XVI synthèse de furo[3,2-c]pyranones-4 et nouvelle voie d'accès aux furo[3,2-c]pyridines

Treatment of 4-hydroxy-6-methylpyran-2-one with chloracetalhyde in basic aqueous medium gave 6-methylfuro[3,2-c]pyran-4-one. This compound reacted with ammonium hydroxide and some primary amines to form the corresponding N-substituted furo[3,2-c]pyrid-4-ones which may also be obtained from 4-hydroxy-α-pyridones. Furo[3,2-c]pyran-4-one was acylated at the 2 position and 4-chloro-6-methylfuro[3,2-c]pyridine easily gave 4-substituted derivatives by displacement of the halogen atom.     

Electrophilic substitution of furo[3,2-c] pyridine

Furo[3,2-c] pyridine (I) was nitrated to give 2-nitrofuro[3,2-c]pyridine (II). Bromination and chlorination of I gave, respectively, 2,3-dibromo-2,3-dihydrofuro[3,2-c]pyridine (III) and 2,3-dichloro-2,3-dihydrofuro[3,2-c]pyridine (IV). Oxidation of I with hydrogen peroxide afforded furo[3,2-c]pyridine 5-oxide (V) which was converted to I by phosphorus trichloride and to 4-chlorofuro[3,2-c]pyridine (VI) by phosphorus oxychloride.     

Studies on furan derivatives. X. Preparation of 2-Methylfuro[2,3-c]quinoline Derivatives

4-Chloro-2-methylfuro[2,3-c]quinoline (IV) was synthesized from ethyl 3-(2-nitrophenyl)-5-methyl-2-furoate and IV was allowed to react with some nucleophiles to afford the corresponding 4-substituted 2-methylfuro-[2,3-c]quinoline derivatives, respectively. On treatment of IV with potassium azide in dimethylsulfoxide, 2-methylfuro[2,3-c]tetrazolo[1,5-a]quinoline was formed path azido-tetrazolo isomerization. 2-Methylfuro-[2,3-c]quinoline was prepared by the reduction of IV.     

Furopyridines. XVII . Cyanation,chlorination and nitration of furo[3,2-b]pyridine N-oxide

The N-oxide 2 of furo[3,2-b]pyridine ( 1 ) was cyanated by the Reissert-Henze reaction with potassium cyanide and benzoyl chloride to give 5-cyano derivative 3 , which was converted to the carboxamide 4 , carboxylic acid 5 , ethyl ester 6 and ethyl imidate 8 . Chlorination of 2 with phosphorus oxychloride yielded 2-9a , 3- 9b , 5- 9c and 7-chloro derivative 9d . Reaction of 9d with sodium methoxide, pyrrolidine, N,N-dimethylformamide and ethyl cyanoacetate afforded 7-methoxy- 10 , 7-(1-pyrrolidyl)- 11 and 7-dimethylaminofuro[3,2-b]pyridine ( 14 ) and 7-(1-cyano-1-ethoxy-carbonyl)methylene-4,7-dihydrofuro[3,2-b]pyridine ( 12 ). Nitration of 2 with a mixture of fuming nitric acid and sulfuric acid gave 2-nitrofuro[3,2-b]pyridine N-oxide ( 15 ).     

Furopyridines. VII. Preparation and hydrolysis of 2-cyano and 3-cyano derivatives of furo[3,2-b]-, furo[2,3-c]- and furo[3,2-c]pyridine

This paper describes the preparation and hydrolysis of 2-cyano and 3-cyano derivatives of furo[3,2-b]-, furo[2,3-c]- and furo[3,2-c]pyridine. Treatment of furopyridines 1a , 1b and 1c with n-butyllithium in hexane-tetrahydrofuran at -70° and subsequent addition of N,N-dimethylformamide yielded 2-formyl derivatives 2a , 2b and 2c. Dehydration of the oximes 4a , 4b and 4c of 2a , 2b and 2c gave 2-cyano compounds 5a , 5b and 5c , which were hydrolyzed to give 2-carboxylic acids, 6a, 6b and 6c , respectively. Reaction of 3-bromo compounds 7a , 7b and 7c with copper(I) cyanide in N,N-dimethylformamide afforded 3-cyano derivatives 8a , 8b and 8c. Alkaline hydrolysis of 8a , 8b and 8c gave compounds formed by fission of the 1-2 bond of furopyridines 9a , 9b and 9c , while acidic hydrolysis gave the corresponding carboxamides, 10a , 10b and 10c.     

Azines polycycliques. (IV). Synthèse de dérivés sulfurés en —3 de l'imidazo[1,5-a]pyridine

2,3-Dihydroimidazo[1,5-a]pyridine-3-thione ( 2 ) was prepared from 2-aminomethylpyridine, and S-alkylated or S-aralkylated. Several reactions of the S-methyl derivative of 2 are reported.     

Synthesis of furo[2,3-b]pyridine

Two routes were employed to synthesize unsubstituted furo[2,3-b]pyridine (IV). The first method started with ethyl 5-aminofuro[2,3-b] pyridine-2-carboxylate (1) and involved successive deamination, hydrolysis, and decarboxylation. The second method began with 5-nitrofuro[2,3-b ]-pyridine-2-carboxylic acid (V) and consisted of successive decarboxylation, reduction, and deamination reactions.     

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.     

Furopyridines. XVIII. Photocycloaddition of furo[2,3-c]pyridin-7(6H)-one with acrylonitrile

The photocycloaddition of furo[2,3-c]pyridin-7(6H)-one ( 1 ) and its N-mefhyl derivative ( 1-Me ) to acrylonitrile has been studied. The structures of the photoadducts isolated by colum chromatography were determined by the nuclear magnetic resonance spectroscopy and single crystal X-ray analysis. The cyclo-addition of 1 afforded an adduct 2 at the carbonyl oxygen and 8-cyano-8,9-dihydrofuro[d]azocin-7(6H)-one ( 3 ), and the addition of 1-Me the N-methyl derivative 3-Me of 3 , (9S*)-9-cyano-6-methyl-3a,7a-dihydro-3a,7a-ethanofuro[2,3-c]pyridin-7(6H)-one ( 4 ), (2S*, 2aR*, 7bR*)- ( 5 ) and (1R*, 2aS*, 7bS*)-2-cyano-3-methyl-4-oxo-1,2,2a,3,4,7b-hexahydrocyclobuta[e]furo[2,3-c]pyridine ( 6 ).     

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.     

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.     

Reaction of 2-alkylthio-6-amino-pyrimidin-4(3H)-ones with ethyl bromopyruvate. Synthesis of furo-[2,3-<Emphasis Type="Italic">d</Emphasis>]-pyrimidine and furo[3,2-<Emphasis Type="Italic">e</Emphasis>]imidazo-[1,2-<Emphasis Type="Italic">c</Emphasis>]pyrimidine carboxylates

Reaction of 2-alkylthio-6-aminopyrimidin-4(3H)-ones with ethyl bromopyruvate to give ethyl 2-alkyl-thio-4-aminofuro[2,3-d]pyrimidine-5-carboxylates has been shown to proceed under neutral or acidic conditions. The obtained furo[2,3-d]pyrimidines underwent further cyclocondensation reaction with ethyl bromopyruvate to afford diethyl 5-alkylthiofuro[3,2-e]imidazo[1,2-c]pyrimidine-2,9-dicarboxy-lates. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 440–443, March, 2009.     

Furopyridines. XXVIII. Reactions of 3-bromo derivatives of furo[2,3-b]-, -[3,2-b]-, -[2,3-c]- and -[3,2-c]pyridine and their N-oxides

Bromination of 3-bromofuro[2,3-b]- 1a , -[3,2-b]- 1b and - [3,2-c]pyridine 1d afforded the 2,3-dibromo derivatives 2a, 2b and 2d , while the -[2,3-c]- compound 1c did not give the dibromo derivative. Nitration of 1a-d gave the 2-nitro-3-bromo compounds 3a-d . The N-oxides 4a-d of 1a-d were submitted to the cyanation with trimethylsilyl cyanide to yield the corresponding α-cyanopyridine compound 6a-d . Chlorination of 4a and 4d with phosphorus oxychloride gave mainly the chloropyridine derivatives 7a, 7′a and 7d , while 4b and 4c gave mainly the chlorofuran derivatives 7′b and 7′c accompanying formation of the chloropyridine derivatives 7b, 7′b and 7c . Acetoxylation of 4a and 4b with acetic anhydride yielded the acetoxypyridine compounds 8a, 8′a and 8b , while 4c and 4d gave the acetoxypyridine 8′c, 8′d and 8′d , pyridone 8c and 8d , acetoxyfuran 8′c and dibromo compound 9c and 9′c.     

Facile synthesis and characterization of novel pyrido[3′,2′:4,5]thieno[3,2-d]pyrimidin-4(3H)-one and pyrido[2′,3′:3,4]pyrazolo[1,5-a]pyrimidine incorporating 1,3-diarylpyrazole moiety

4-(3-(4-Hydroxyphenyl)-1-phenyl-1H-pyrazol-4-yl)-6-phenyl-2-thioxo-1,2-di hydro-pyridine-3-carbonitrile (1) reacted with ethyl chloroacetate (2) in ethanolic sodium acetate solution to yield the corresponding ethyl (3-cyanopyridin-2-ylsulphanyl)acetate derivative 3. Intramolecular cyclization of compound 3 was achieved by its heating in DMF containing potassium carbonate to afford the corresponding ethyl 3-aminothieno[2,3-b]pyridine-2-carboxylate derivative 4 which reacted with hydrazine hydrate in refluxing pyridine to yield the starting material 3-aminothieno[2,3-b]pyridine-2-carbohydrazide derivative 7. Compound 7 reacted with different reagents such as triethylorthoformate, formic acid, acetic acid and acetic anhydride to afford the target molecules pyrido[3′,2′:4,5]thieno[3,2-d]pyrimidin-4(3H)-one derivatives 8–10, 12 and 13 in good to excellent yields. On the other hand, pyridine-2(1H)-thione derivative 1 reacted with hydrazine hydrate in refluxing pyridine to give the other starting material 3-amino-1H-pyrazolo[3,4-b]pyridine derivative 20 which reacted with acetylacetone under reflux to afford the target molecule pyrido[2′,3′:3,4]pyrazolo[1,5-a]-pyrimidine derivative 21 in a good yield. The structures of target molecules were elucidated using elemental analyses and spectral data.