Synthesis of 1H-pyrazolo[3,4-e]-s-triazolo[3,4-c]-as-triazines, 8H-pyrazolo[3,4-e]tetrazolo[5,1-c]-as-triazine and 1,7-dihydro-8H-pyrazolo[3,4-e]-as-triazine derivatives

3-Hydrazino-7-methyl-5-phenyl-5H-pyrazolo[3,4-c]-as-triazine 1 underwent ring closure and/or condensation reaction with formic acid, acetic acid, acetic anhydride and benzoyl chloride to afford 1H-pyrazolo-[3,4-d]-s-triazolo[3,4-c]-as-triazines 2, 5 and 7a and/or N-acyl derivatives 3, 4 and 6 . N-Acyl derivatives 3 and 6 underwent cyclisation reaction on treatment with phosphoryl chloride to give 5 and 7a . 3-Methyl-1-phenyl-8-aryl-1H-pyrazolo[3,4-e]-s-triazolo[34,-c]-as-triazines 7 were also prepared by the reaction of the hydrazono derivatives 8 wit thionyl chloride. On treatment of 1 with nitrous acid gave the 8H-pyrazolo[3,4-e]tetrazolo-[5,1-c]-as-triazine 9 . Compound 1 underwent ring closure with carbon disulphide or ethyl chloroformate to 1,7-dihydro-8H-pyrazolo[3,4-e]-s-triazolo[3,4-c]-as-triazine derivatives 10 and 12 . Reaction of 1 with ethyl acetoacetate or acetylacetone gave 3-pyrazolo derivatives 13 and 14 .     

4-Azapteridines. I. Covalent addition products of the pyrazino[2,3-e]-as-triazine ring system

Ring closure of 5, 6-diamino-3-methylthio-as-triazine with 40% aqueous glyoxal provided the 6, 7-dihydrate of the pyrazino[2, 3-e]-as-triazine (4-azapteridine) ring system. The C7 hydroxy group of this dihydrate underwent exchange in methanol or ethanol affording the 7-alkoxy, 6-hydroxy derivatives.     

Synthesis and spectral data of pyrido[2,3-e]-as-triazines

The pyrido[2,3-e]-as-triazine and its 3-phenyl derivatives were prepared via cyclisation with polyphosphoric acid of suitable 3-substituted 2-aminopyridines obtained by reduction of the corresponding 2-nitropyridines. The 3-substituted 2-nitropyridines were obtained by action of hydrazine or benzoylhydrazide with the appropriate 3-halo-2-nitropyridines; only 3-fluoro-2-nitropyridine leads to the 3-substituted 2-nitropyridines. This experimental results are in agreements with the CNDO and MNDO calculations.     

Synthesis and Properties of Derivatives of the new Heterocyclic System Benz[4,5]imidazo[1,2-c]pyrido[3',2';4,5]thieno[2,3-e]pyrimidine

Derivatives of a new heterocyclic system - benz[4,5]imidazo[1,2-c]pyrido[3',2';4,5]thieno[2,3-e]pyrimidine have been obtained by successive reactions in three stages - alkylation of 3-cyanopyridine-2(1H)-thiones with 2-chloromethylbenzylimidazole to give 2-benzimidazolylmethylthio-3-cyanopyridines, closing the thiophene ring in the latter to form 3-amino-2-(benzimidazolyl-2)thieno[2,3-b]pyridines, and cyclization of the pyrimidine ring by acylation with carboxylic acid anhydrides or chlorides.     

Synthesis of pyrido[3,2-e]pyrrolo[2,1-c][1,2,4]triazines from pyrido[3,2-e][1,2,4]triazine derivatives

In carrying on our interest in heteropolycyclic structures with biological activities, we projected the preparation of compounds containing the pyrido[3,2-e][1,2,4]triazine or pyrido[2,3-b][1,4]triazepine systems. The established synthetic approach for the preparation of latter system led to the triazine derivatives 5a-f while a new bicyclic triazepine structure 6 is accomplished with difficulty. In expanding the pyridotriazine structure, we obtained derivatives of a new tricyclic structure, 5-substituted-6a-ethyloxycarbonyl-5,6,6a,7-tetrahydropyrido[2,3-e]pyrrolo[2,1-c][1,2,4]triazin-9(8H)-ones 8 in which the triazine ring is fused with a pyrrole nucleus. Compounds 5a-f and 8a,b will be tested as potential CNS depressant, antiinflammatory, analgesic and antibacterial agents.     

Azinotriazines. II Cyclizations leading to pyrido[3,4-e] - and [4,3-e]-as-triazines. Ring interconversion of a pyrido-as-triazine 1-oxide to a pyridotriazole

Treatment of 4-chloro-3-nitropyridine (I) with hydrazine hydrate followed by catalytic reduction gave 3-amino-4-hydrazinopyridine (III). Acid-catalyzed cyclizations of III and subsequent dehydrogenation gave pyrido[3,4-e]-as-triazines (V). Treatment of I with guanidine followed by base-catalyzed cyclization gave 3-aminopyrido[4,3-e]-as-triazine 1-oxide (VII). The 1-oxide function was removed by reduction and subsequent dehydrogenation gave the 3-amino derivative (IX). On treatment with hot alkali VII rearranged to a triazolo[4,5-c]pyridine (X). The ultraviolet and nmr spectra of derivatives of the title ring systems are reported.     

The synthesis and properties of pyridazino[4,3-e] -as-triazines and pyridazino[4,5-e] -as-triazines,two novel condensed pyridazine ring systems

The compounds prepared in the novel pyridazino[4,3-e]-as-triazine ring system are: 8-chloro-4-methyl-3,4-dihydropyridazino[4,3-e]-as-triazine ( 21 ), 8-chloro-2,4-dimethyl-3,4-dihydropyridazino[4,3-e]-as-triazine ( 23 ), 8-chloro-2-ethyl-4-methyl-3,4-dihydropyridazino[4,3-e]-as- triazine ( 24 ), 4-methyl-3,4-dihydropyridazino[4,3-e]-as-triazine-8-thione ( 25 ), 4-methyl-3,4-dihydropyridazino[4,3-e]-as-triazine ( 26 ), 2,4-dimethyl-3,4-dihydropyridazino[4,3-e]-as-triazine ( 27 ), and 2-ethyl-4-methyl-3,4-dihydropyridazino[4,3-e]-as-triazine ( 28 ). In the novel pyridazino[4,5-e]-as-triazine ring system the following compounds were prepared: 1,2-dihydropyridazino[4,5-e]-as-triazine ( 31 ), 3-methyl-1,2-dihydropyridazino[4,5-e]-as-triazine ( 32 ), 3-ethyl-1,2-dihydropyridazino[4,5-e]-as-triazine ( 33 ), and 1-methyl-1,2-dihydropyridazino[4,5-e]-as-triazine ( 35 ). The preparation of a number of previously unreported intermediates and compounds for structure proof are also described.     

New [g]-fused [1,2,4]triazolo[1,5-c]pyrimidines: Synthesis of pyrido[3,2-e] and [4,3-e][1,2,4]triazolo[1,5-c]pyrimidine,pyrimido[5,4-e][1,2,4]triazolo[1,5-c]pyrimidine and [1,2,4]triazolo[1,5-c]pteridine derivatives

A number of 2-aryl-substituted pyrido[3,2-e] and [4,3-e][1,2,4]triazolo[1,5-c]pyrimidines and [1,2,4]triazolo[1,5-c]pteridines 11,12a,b,e , their corresponding 5-carbonyl derivatives 7,8a,b,e and some pyrimido[5,4-e][1,2,4]triazolo[1,5-c]pyrimidin-5-ones 7,8c,d have been synthesized, according to different pathways. The new tricyclic heterocycles were prepared with the aim of studying their possible benzodiazepine receptors affinity.     

Azinotriazines. I. Synthesis and spectral data of pyrido[3,2-e] -as-triazines

A series of pyrido[3,2-e]-as-triazines (VI) was prepared via acid-catalyzed cyclization of suitable 2-substituted 3-aminopyridines obtained by reduction of the corresponding 3-nitro-pyridines. Cyclization of 3-amino-2-hydrazinopyridines (III) with triethyl orthoformate and hydrochloric acid, or cyclodehydration of 2-(2-acetylhydrazino)-3-aminopyridines (IV) with alcoholic hydrogen chloride gave 1,2-dihydropyrido[3,2-e]-as-triazine hydrochloride (V). Mild dehydrogenation with alkaline potassium ferricyanide yielded heteroaromatic pyrido[3,2-e]-as-triazines (VI), for which ultraviolet and nmr spectral data are reported.     

The synthesis of [1]benzothieno[2,3-c]quinolines, [1]benzothieno[2,3-c][1,2,4]triazolo[4,3-a]quinoline,and [1]benzothieno[2,3-c]tetrazolo[1,5-a]quinoline

Photocyclization of 3-chloro-N-phenylbenzo[b]thiophene-2-carboxamide 10 afforded [1]benzothieno[2,3-c]-quinolin-6(5H)-one 11 which was chlorinated to 6-chloro[1]benzothieno[2,3-c]quinoline 12 followed by dechlorination to give [1]benzothieno[2,3-c]quinoline 5 . A series of 6-substituted alkoxy and thioalkoxy[1]benzothieno[2,3-c]quinoline derivatives were prepared along with the N-methyl quaternary salt 13 of 5 . 6-Chloro[1]-benzothieno[2,3-c]quinoline 12 was converted into 6-hydrazino[1]benzothieno[2,3-c]quinoline 23 which upon treatment with formic acid yielded [1]benzothieno[2,3-c][1,2,4]triazolo[4,3-a]quinoline 6 . Treatment of 23 with nitrous acid resulted in [1]benzothieno[2,3-c]tetrazolo[1,5-a]quinoline 7 . Compounds 6 and 7 are novel heterocyclic ring systems.     

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.     

4-Azapteridines. 2. spectral,chromatographic, and X-Ray crystallographic studies concerning the mode of covalent addition to the pyrazino[2,3-e]-as-triazine ring system

The first examples of the unknown pyrazino[2,3-e]-as-triazine ring system, that is, the 6,7-dihydroxy-5,6,7,8-tetrahydropyrazino[2,3-e]-as-triazines, have been prepared by ring closure of selected 5,6-diamino-as-triazines with 40% aqueous glyoxal. These 4-azapteridines experience a novel exchange process with alcohols at the C(7)-position. When dissolved in alcohol and stirred at room temperature, the 7-alkoxy, 6-hydroxy analogues are formed and isolated. In fact, during ring closure, if alcohols are used as the solvent, only the latter compounds are obtained. Initially, cyclization of the ortho-diamino-as-triazines with glyoxal proceeds in a stereoselective manner giving rise to both the cis and trans adducts. A single-crystal X-ray diffraction study has determined the predominant and most stable adduct to be the trans (R,R or S,S) isomer. Spectroscopy (nmr) has verified the intermediacy of the cis adduct, but because of the aforementioned exchange process only the trans isomer is isolated. The site of exchange on these σ-adducts has been rigorously established as C(7). A plausible reaction mechanism by which this exchange process occurs is presented.     

5H-Thiazolo [3,2-b]- and 2H-Thiazolo [2,3-c]-as-triazines

Derivatives of the 5H-thiazolo[3,2-b]- and 2H-thiazolo[2,3-c]-as-triazine systems were synthesized via condensation of tetrahydro-I-methyl-as-triazine-3(2H)-thione with ethylene dibromide and ethyl bromoacetate, respectively. An hypothesis is given for the formation of the [3,2-b] system in one of these reactions and the [2,3-c] system in the other. Structure proof was accomplished by an unequivocal synthesis of one of the [2,3-c] derivatives.     

Synthesis of thieno[2,3-e]-1,2,4-triazines

3-Methylmercapto-5-oxo-6-vinyl- and 2-methyl-3-mercapto-5-oxo-6-vinyl-2,5-dihydro-1,2,4-triazines were readily converted into the corresponding thieno[2,3-e]-1,2,4-triazine in one step by the action of phosphorus pentasulfide in pyridine. 4-Methyl-3-mercapto-5-oxo-4,5-dihydro-1,2,4-triazine is only converted into the 5-thioxo analog and no thiophene ring product was obtained under the same conditions. Thieno[2,3-e]-1,2,4-triazines were also more efficiently obtained by the action of phosphorus petnasulfide in pyridine on the appropriate 6-acylmethyl-3-mercapto-5-oxo-2,5-dihydro-1,2,4-triazine.     

Annulation reactions of 3-aminoisoquinolin-l(2H)-one. Synthesis of pyrimido[1,2-b]isoquinolines,pyrido-[2,3-c]isoquinolines and pyrrolo[2,3-c]isoquinolines

Reactions of the title compound with the malonic acid derivatives diethyl ethoxymethylenemalonate (EMME), ethyl ethoxymethylenecyanoacetate (EMCA) and ethoxymethylenemalononitrile (EMMN) are reported. Condensations occur at the amino group or C-4, depending on conditions and the former intermediate was successfully cyclized to the pyrimido[1,2-b]isoquinoline system. Reactions with 2,4-pentanedione and p-bromophenacyl bromide gave only the angular systems, pyrido[2,3-c]isoquinoline and pyrrolo[2,3-c]isoquin-oline, respectively.     

A new synthesis of pyrimido[5,4-e]-as-triazine 4-oxides and their ring transformation to pyrrolo[3,2-d]pyrimidines

A new synthesis of certain pyrimido[5,4-e]-as-triazine 4-oxides and their ring transformation to pyrrolo-[3,2-d]pyrimidines by the 1,3-dipolar cycloaddition reaction is described. Thus, reaction of 6-hydrazino-1,3-dimethyluracil ( 1 ) with triethyl orthoformate gave 6-ethoxymethylenehydrazino-1,3-dimethyluracil ( 2 ). Treatment of 2 with arylamines gave 6-arylaminomethylenehydrazino-1,3-dimethyluracils ( 3a-e ). Nitrosative cyclization of 3a-e with sodium nitrite afforded 3-arylaminofervenulin 4-oxides ( 6a-e ). Reaction of 6a-e with acetylenic esters yielded 7-alkoxycarbonyl-6-arylamino-1,3-dimethylpyrrolo[3,2-d]pyrimidine-2,4(1H,3H-diones ( 15a-e and 16 ).     

Synthesis of novel imidazo[1,2-a][3,1]benzothiazines 4, imidazo[1,2-a]-[1,2,4]benzotriazines 5, and 4H-imidazo[2,3-c]pyrido[2,3-e][1,4]oxazines 6

Starting from the readily available 2-aminobenzhydrols ( 7 ), 3-amino-1,2,4-benzotriazine ( 11 ) and 2-amino-3-pyridinol ( 12 ), novel derivatives of 5-phenyl-5H-imidazo[1,2-a][3,1]benzothiazine-2-carboxylic acid, ethyl ester ( 4 ), imidazo[2,1-c][1,2,4]benzotriazine-2-carboxylic acid, ethyl ester ( 5 ) and 4H-imidazo[2,3-c]pyrido-[2,3-e][1,4]oxazine ( 6 ) were prepared.     

The synthesis of a pyrido[2,3-c]pyridazine: A cinnoline related to 6-fluoronalidixic acid

An analog of the pyrido[2,3-c]pyridazine ring system, 1-ethyl-6-fluoro-1,4-dihydro-7-methyl-4-oxopyrido-[2,3-c]pyridazine-3-carboxylic acid ( 13 ), related to both Cinoxacin ( 1 ) and nalidixic acid ( 2 ), has been synthesized. The reductive ring closure of 2-chloro-α-diazo-6-methyl-5-nitro-β-oxo-3-pyridinepropanoic acid, ethyl ester ( 7 ), proved to be the key reaction providing entry into the ring system.     

Reactions with heterocyclic diazonium salts: New routes for the synthesis of pyrazolo[1,5-c]-1,2,4-triazoles and pyrazolo[1,5-c]-as-triazines

3-Phenylpyrazole-5-(liazonium chloride ( 1 ) couples with α-chloro derivatives of acetylacetone, ethyl acetoacetate and aceto-o-anisidine to yield the corresponding pyrazole-5-yl hydrazonyl chloride derivatives 2a-c . Compounds 2a,b were cyclised to yield either the pyrazolo[1,5-c]-1,2,4-triazole derivatives 3a,b or the pyrazolo[1,5-c]-as-triazines 4a,b depending on the applied reaction conditions. Compound 2c cyclised only into 3c under different cyclization conditions. The pyrazolo[1,5-c]-as-triazine derivatives 4c-e could be prepared via condensation of 2a with potassium cyanide. Compound 2d reacted with aromatic thioles and with sodium benzene-sulphonate to yield the pyrazolo[1,5-c]-as-triazine derivatives 6a-d . Compound 1 reacted with activated double bond systems to yield pyrazolo[1,5-c]-as-triazines 8a,b and 9 .     

Diethyl ethoxymethylenemalonate in triheterocycles: A new synthesis of pyrido[3,2-e]pyrimido[1,2-c]pyrimidines

Diethyl ethoxymethylenemalonate was used for the novel synthesis of the triheterocyclic 3-carbethoxy-9,ll-disubstituted-4-oxo-4H-pyrido[3,2-e]pyrimido[1,2-c]pyrimidines from 4-aminopyrido[2,3-d]pyrim-idines via thermal cyclization of the intermediate ethyl 2-carbethoxy-3-[5,7-disubstituted-4-amino-pyrido[2,3-d]pyrimidin-4-yl]acrylates. The alkaline hydrolysis of 3-carbethoxy-4-oxo-4H-pyrido[3,2-e]-pyrimido[1,2-c]pyrimidines was performed to give corresponding acid derivatives.