A facile and novel synthesis of 1,6-naphthyridin-2(1H)-ones

A new and convenient procedure for the synthesis of 1,6-naphthyridin-2(1H)-ones and their derivatives is described. In the first scheme 5-acetyl-6-[2-(dimethylamino)ethenyl]-1,2-dihydro-2-oxo-3-pyridinecarbonitrile ( 4 ) obtained by the reaction of N,N-dimethylformamide dimethyl acetal with 5-acetyl-1,2-dihydro-6-methyl-2-oxo-3-pyridinecarbonitrile ( 3 ) was cyclized to 1,2-dihydro-5-methyl-2-oxo-1,6-naphthyridine-3-carbonitrile ( 5 ) by the action of ammonium acetate. Thermal decarboxylation of acid 7 obtained from the hydrolysis of nitrile 5 led to a mixture of 5-methyl-1,6-naphthyridin-2(1H)-one ( 8 ) and its dimer 9 . Hydrazide 11 obtained from nitrile 5 in two steps was converted to 3-amino-5-methyl-1,6-naphthyridin-2(1H)-one ( 12 ) by the Curtius rearrangement. The amino group of 12 was readily replaced by treatment with aqueous sodium hydroxide to yield 3-hydroxy-5-methyl-1,6-naphthyridin-2(1H)-one ( 13 ). In the second scheme, Michael reaction of enamines of type 20 with methyl propiolate, followed by ring closure gave 5-acyl(aroyl)-6-methyl-2(1H)-pyridinones ( 21 ) which in turn were treated with Bredereck's reagent to produce 5-acyl(aroyl)-6-[2-(dimethylamino)ethenyl]-2(1H)-pyridinones ( 22 ). Treatment of 22 with ammonium acetate led to the formation of 1,6-naphthyridin-2(1H)-ones 23 .     

Synthesis and heterocyclization of 2-{[2-(4-bromophenyl)-2-oxoethyl]sulfanyl}pyrimidin-4(3<Emphasis Type="Italic">h</Emphasis>)-ones

Alkylation of sodium 4(5)-alkyl-6-oxo-1,6-dihydropyrimidine-2-thiolates with 2-bromo-1-(4-bromophenyl)ethan-1-one afforded 2-{[2-(4-bromophenyl)-2-oxoethyl]sulfanyl}pyrimidin-4(3H)-ones. Analogous reaction with sodium 4-trifluoromethyl-6-oxo-1,6-dihydropyrimidine-2-thiolate gave a mixture of 2-{[2-(4-bromophenyl)-2-oxoethyl]sulfanyl}-4-(trifluoromethyl)pyrimidin-4(3H)-one and its intramolecular cyclization product, 3-(4-bromophenyl)-3-hydroxy-7-trifluoromethyl-2,3-dihydro[1,3]thiazolo[3,2-a]-pyrimidin-5-one.     

Strategic studies in the syntheses of novel 6,7-substituted quinolones and 7- or 6-substituted 1,6- and 1,7-naphthyridones

This paper describes the different strategies devised and applied to overcome the selectivity issues in the syntheses of 6,7-disubstituted-1H-quinolin-4-one, 7-substituted-1H-1,6-naphthyridin-4-one and 6-substituted-1H-1,7-naphthyridin-4-one derivatives. They allowed us to improve the overall yields and the scaling-up feasibility. Several examples illustrate these strategies with their advantages and drawbacks.     

A facile and novel synthesis of 5-phenylimidazo[4,5-c][1,8]naphthyridin-4(5H)-ones

A convenient and regioselective synthesis of a new heterocycle, 5-phenyl-1H or 3H-imidazo[4,5-c][1,8]-naphthyridin-4(5H)-one 1-a or 1-b , is described. Methyl 2-anilinonicotinate 15 was transformed into the valuable intermediate, N-phenyl-3-azaisatoic anhydride 4 using trichloromethyl chloroformate (TCF). Treatment of 4 with the anion of ethyl nitroacetate gave 4-hydroxy-3-nitro-1-phenyl-1,8-naphthyridin-4(5H)-one 3 . Compound 3 was chlorinated, aminated, reduced, and cyclized to afford 5-phenylimidazo[4,5-c][1,8]naphthyridin-4(5H)-one 1 . Regioselective substitution at the 1 or 3-position in the imidazole moiety of 1 was achieved by minor changes of the above scheme.     

Über die Synthese von 5-(o-Chlorphenyl)-7-trifluormethyl-1Hthieno[3,2—e]-1,4-diazepin-2(3H)-on

The synthesis of 5-(o-chlorophenyl)-7-trifluoromethyl-1H-thieno[3.2?e]-1.4-diazepin-2(3H)-one (10) starting from ethyl 3-amino-5-trifluoromethyl-2-thiophenecarboxylate (1) is described.     

Synthesis of naphthyridinone derivatives as potential antimalarials

In this paper we present the synthesis of 8-(4′-amino-1′methyl-butylamino)-5-(β,β,β-trifluoroethoxy)-1,6-naphthyridine ( 4 ), 8-(4′-amino-1′methylbutylamino)-6-methyl-1,6-naphthyricline-5-one ( 5 ), two 1-alkyl-3-(4′-amino-1′-methylbutylamino)-7-methyl-1,8-naphthyridin-4-ones ( 20a ) and 20b ), 3-(1′-amino-4′-methylbutyl-amino)-l-ethyl-7-methyl-l,8-naphthyridin-4-one (20c), and 4-(4′-diethylamino-1′-methylbutylamino)-7-methyl-1,7-naphthyridin-8-one ( 28 ). The compounds were evaluated for antimalarial activity in the Plasmodium berghei screen and found to be inactive.     

Grignard Reagent Utilization Enables a Practical and Scalable Construction of 3-Substituted 5-Chloro-1,6-naphthyridin-4-one Derivatives

A robust, practical, and scalable approach for the construction of 3-substituted 5-chloro-1,6-naphthyridin-4-one derivatives 13 via the addition of Grignard reagents to 4-amino-2-chloronicotinonitrile (15) was developed. Starting with various Grignard reagents, a wide range of 3-substituted 5-chloro-1,6-naphthyridin-4-one derivatives 13 were conveniently synthesized in moderate-to-good yields through addition–acidolysis–cyclocondensation. In addition, the robustness and applicability of this synthetic route was proven on a 100 g scale, which would enable convenient sample preparation in the preclinical development of 1,6-naphthyridin-4-one-based MET-targeting antitumor drug candidates.     

1,2,4-Triazines, 9. The synthesis of novel 4-amino-1,6-dihydro-1,2,4-triazinones

3-Alkylthio-4-amino-1,6-dihydro-1,2,4-triazin-5(4H)-ones were synthesized by the reduction of 3-thio-4-amino-1,2,4-triazine-3,5(2.H,4H)-diones and successive S-alkylation. The regiospecific alkylation on the N-1 position or the exo amino group leads to a variety of 1,6-dihydro-1,2,4-triazin-5(4H)-one derivatives. An alternative synthesis of 3-thio-4-amino-1,6-dihydro-1,2,4-triazine-3,5(2H,4H)-diones was accomplished through the cyclization of 1-thiocarbohydrazidoacetamide derivatives.     

New heterocyclic derivatives of trifluoroalanine

A new method of the synthesis of heterocyclic derivatives of trifluoroalanine based on the cyclocondensation of methyl trifluoropyruvate tert-butoxycarbonylimine with C,N- and N,N-binucleophiles, like Nsubstituted ureas, 1-benzyl-6-aminouracil, benzamidine, and 3-aminocrotononitrile, followed by hydrolysis of the resulting Boc-derivatives to 5-amino-5-trifluoromethylimidazolidine-2,4-diones, 5-amino-5-trifluoromethyl-1-benzyl-5,7-dihydropyrrolo[2,3-d]-pyrimidine-2,4,6-3H-trione, 4-amino-2-methyl-5-oxo-4-(trifluoromethyl)-4,5-dihydro-1H-pyrrole-3-carbonitrile, or 5-amino-5-trifluoromethyl-2-phenyl-3,5-dihydroimidazol-4-one, respectively, was developed.     

Isoquinolin-1(2H)-ones and 1,6-naphthyridin-5(6H)-ones by an N-acylation-SNAr sequence

A new synthesis of 2,3-dialkyl-4-carbomethoxyisoquinolin-1(2H)-ones and 6,7-dialkyl-8-carbomethoxy-1,6-naphthyridin-5(6H)-ones is reported. The process involves treatment of a β-enaminoester with 2-fluoro-5-nitrobenzoyl chloride, 2-fluorobenzoyl chloride or 2-chloronicotinoyl chloride followed by heating in the presence of base. The conversion, which proceeds by an N-acylation-S_NAr reaction sequence, affords 50–86% yields when R¹ is n-alkyl but ≤30% yields when R¹ is α-branched.     

1,2,4-Triazines. 8. Reduction of 4-methyl-1,2,4-triazin-5(4H)-ones with sodium borohydride. Regioselective preparation of dihydro-1,2,4-triazin-5(4H)-ones

Reduction of 3-methylthio-1,2,4-triazin-5(4H)-one ( 1a ) with sodium borohydride afforded 3-methylthio-1,6-dihydrotriazin-5(4H)-one ( 2b ) selectively. 3-Methylthio-6-t-butyl-1,2,4-triazin-5(4H)-one ( 1d ) reacted with sodium borohydride to give mainly 6-t-butyl-2,3-dihydro-1,2,4-triazin-5(4H)-one ( 3d ). The reaction of various 4-methyl-1,2,4-triazin-5(4H)-ones with sodium borohydride and the influence of bulkiness and electronic effect of the substituents at the 3- and 6-positions upon the product ratio, are also discussed.     

Reaction of 1,3,4,6-tetraketones with <Emphasis Type="Italic">p</Emphasis>-toluidine and benzaldehyde

Reactions of 1,6-diphenylhexane-1,3,4,6-tetraone, octane-2,4,5,7-tetra-one, and decane-3,5,6,8-tetraone with a mixture of p-toluidine and benzaldehyde afforded, respectively, 2-[4-benzoyl-3-hydroxy-1-(4-methylphenyl)-5-phenyl-1H-pyrrol-2-yl]-1-phenylethanone, (1E)-1-[4-acetyl-3-hydroxy-1-(4-methylphenyl)-5-phenyl-1,5-dihydro-2H-pyrrol-2-ylidene]propan-2-one, and 2-hydroxy-1-(4-methylphenyl)-2-(2-oxobutyl)-4-propanoyl-5-phenyl-1,2-dihydro-3H-pyrrol-3-one.     

Synthesis of the dibenzo[f,h]phthalazine and dibenzo[f,h]cinnoline skeleton via a ‘Suzuki-Pd-catalyzed intramolecular arylation’ and a ‘Suzuki-Pschorr’ approach

Palladium-catalyzed intramolecular arylation of 2-benzyl-5-(2-bromophenyl)-4-phenylpyridazin-3(2H)-one yielded hitherto unknown 2-benzyldibenzo[f,h]phthalazin-1(2H)-one. The synthesis of this new tetracyclic pyridazinone from 2-benzyl-5-(2-aminophenyl)-4-phenylpyridazin-3(2H)-one via a Pschorr type reaction was also investigated. Similarly, the construction of 2-methyldibenzo[f,h]cinnolin-3(2H)-one from 2-methyl-5-(2-bromophenyl)-6-phenylpyridazin-3(2H)-one and 2-methyl-5-(2-aminophenyl)-6-phenylpyridazin-3(2H)-one is also reported. Removal of the N-benzyl protective group of 2-benzyl-dibenzo[f,h]phthalazin-1(2H)-one with AlCl₃ yielded unsubstituted dibenzo[f,h]phthalazin-1(2H)-one.     

Synthesis of 2-aryl-2-trifluoromethyl-1,3-thiazolidin-4-ones and 2-aryl-2-trifluoromethyltetrahydro-4<Emphasis Type="Italic">H</Emphasis>-1,3-thiazin-4-ones and their oxidation with hydrogen peroxide

Reactions of aryl trifluoromethyl ketone imines with 2-sulfanylacetic and 3-sulfanylpropanoic acids afforded 2-aryl-2-trifluoromethyl-1,3-thiazolidin-4-ones and 2-aryl-2-trifluoromethyltetrahydro-4H-1,3-thiazin-4-ones, respectively. Their subsequent oxidation with hydrogen peroxide gave the corresponding 2-aryl-2-trifluoromethyl-1,3-thiazolidin-4-one 1-oxides and 2-aryl-2-trifluoromethyltetrahydro-4H-1,3-thiazin-4-one 1-oxides and 1,1-dioxides.     

3-Oxo-4,4,4-trifluorobutyronitriles as building blocks of trifluoromethyl substituted heterocycles 2. Heterocyclization to 3-aryl-4-trifluoromethyl-2H-1-benzopyran-2-ones under hoesch reaction conditions

Resorcinol and 5-methylresorcinol, respectively, react with 3-oxo-2-aryl-4,4,4-trifluorobutyronitrile using zinc chloride as a catalyst in dibutyl ether under the Hoesch reaction conditions to give a low yield of 3-aryl-7-hydoxy-4-trifluoromethyl- or 3-aryl-5-hydroxy-7-methyl-4-trifluoromethyl-2H-l-benzopyran-2-ones. However, the related reaction with m-methoxyphenol was found to produce poor yields of 3-aryl-7-methoxy-4-trifluoromethyl-2H-1-benzopyran-2-one and its 3,4-dihydro-4-hydroxy derivative.     

Cyclizations of monocyclic 5-nitropyridin-2(1<Emphasis Type="Italic">H</Emphasis>)-ones

Reactions of 5-nitropyridin-2(1H)-one and its N-methyl derivative with hydrazine hydrate led to the formation of (1H-pyrazol-3-yl) acetohydrazide. Under analogous conditions, 1,3-dimethyl-5-nitropyridin2(1H)-one gave rise to 2-(1H-pyrazol-3-yl)propionohydrazide, while 6-methyl-5-nitropyridin-2(1H)-one was converted into (5-methyl-1H-pyrazol-3-yl)acetohydrazide. Hydrazinolysis of 4-methyl-5-nitropyridin-2(1H)-one resulted in the formation of 3-methyl-4-nitro-1H-pyrazole. The mechanism of recyclization of nitropyridine derivatives by the action of hydrazine hydrate was studied using 5-nitropyridin-2(1H)-one and 1-methyl-5-nitropyridin-2(1H)-one as examples.     

From Levulinic Acid to Biheterocycles: Synthesis of 1-[(5-Hydroxy-5-trifluoromethyl-3-substituted-4,5-dihydro-1H-pyrazol-1-yl)-3-(5-trifluoromethyl-1H-pyrazol-3-yl)propan-1-ones

We develop an efficient method to synthesize novel propionyl-spaced bisheterocyclic compounds. It entails cyclocondensation of 3-(5-trifluoromethyl-1H-pyrazol-3-yl)propanoyl hydrazide obtained from levulinic acid, with 1,1,1-trifluoro-4-methoxy-3-alken-2-ones proceeding regiospecifically to 1-[(5-trifluoromethyl-5-hydroxy-3-substituted-4,5-dihydro-1H-pyrazol-1-yl)-3-(5-trifluoromethyl-1H-pyrazol-3-yl)propan-1-one derivatives.     

1,6- and 1,7-naphthyridines. II. Synthesis from acyclic precursors

A number of 8-hydroxy-6-methyl-1,6-naphthyridin-5(6H)-one-7-carboxylic acid alkyl esters 3 and the isomeric 5-hydroxy-7-methyl-1,7-naphthyridin-8(7H)-one-6-carboxylic acid alkyl esters 4 were synthesized from acyclic precursors obtained starting from quinolinic anhydride 5. Thus, methanolysis of 5 afforded the hemiester 6 which treated with oxalyl chloride and sarcosine ethyl ester gave 3-(N-ethoxycarbonylmethyl-N-methylcarbamoyl)pyridine-2-carboxylic acid methyl ester 8. Compound 8 was cyclized to naphthyridines 3a-e with sodium alkoxides. The isomeric naphthyridines 4a-c were obtained by cyclization of the open intermediary 2-(N-ethoxycarbonylmethyl-N-methylcarbamoyl)pyridine-3-carboxylic acid methyl ester 9 obtained by a route that involves treatment of 5 with sarcosine ethyl ester and esterification with diazomethane. Spectroscopic properties (¹H nmr, uv, ir) of compounds 3 and 4 are discussed and confirmed the proposed structures.     

Direct introduction of heterocyclic residues into 1,2,4-triazin-5(2H)ones

3-Aryl-1,2,4-triazin-5(2H)-ones 1a-c react with indoles 2a-c in trifluoroacetic acid/chloroform or in boiling butanol or acetic acid to give 3-aryl-6-(indolyl-3)-1,6-dihydro-1,2,4-triazin-5(2H)-ones 3a-g . Oxidation of the dihydro-1,2,4-triazin-5(2H)-ones 3a-e afforded 6-(indolyl-3)-1,2,4-triazin-5(2H)-ones 4a-e , products of nucleophilic substitution of hydrogen in 1a-c . Refluxing 1b with N-methylpyrrote 5b in butanol for an extended time resulted in the formation of 3-(4-chlorophenyl)-6-(1-meuiylpyrrolyl-2)-1,2,4-triazin-5(2H)-one 4h. The reaction of 1a-c with indoles 2a-c , pyrroles 5a,b , 1,3-dimethyl-2-phenylpyrazol-4-one (8) and aminothiazoles 9a,b in acetic anhydride affords the 1-acetyl-3-aryl-6-hetaryl-1,6-dihydro-1,2,4-triazin-5(2H)-ones 6a-s . Reaction of 1a-c with N-methyl-pyrrole 5b in acetic anhydride gives beside the 1:1 addition products 6h-k also the 2:1 addition products 7a-c .     

A convenient one-pot synthesis of 2-(trifluoromethyl)-3,4,7,8-tetrahydro-2H-chromen-5(6H)-one derivatives and their further transformations

The trifluoromethyl containing heterocycles, 2-hydroxy-4-aryl-3-(thien-2-oyl)-2-(trifluoromethyl)-3,4,7,8-tetrahydro-2H-chromen-5(6H)-one derivatives 4, were synthesized via a one-pot three-component reaction of aldehyde 1 with 1,3-cyclohexanedione 2 and 4,4,4-trifluoro-1-(thien-2-yl)butane-1,3-dione 3 in the presence of a catalytic amount of Et₃N. The effect of bases and solvents on the reaction efficiency and yield was briefly investigated. Treatment of 4 with an excess amount of NH₄OAc in ethanol afforded 2-trifluoromethyl-1H-quinolin-5-one derivatives 5. Refluxing of 4 with TsOH in CHCl₃ gave the corresponding dehydrated products 8.