Synthesis of 6-(arylthio)- and 6-[(arylmethyl)thio] -1,2,4,5-tetrazin-3-amines and n-phenyl- and n-(phenylmethyl)-1,2,4,5-tetrazine-3,6-diamines as potential antimalarial agents

Alkylation of tetrahydro-1,2,4,5-tetrazine-3,6-dithione with iodomethane and 1,2-dichloro-4-(chloromethyl)benzene, respectively (Scheme 1, 4 ) followed by oxidation afforded 3,6-bis(methylthio)- and 3,6-bis[[(3,4-dichlorophenyl)methyl]thio]-1,2,4,5-tetrazines ( 6, 15 ). The reaction of 15 with amines provided the 6-[(arylmethyl)thio]-1,2,4,5-tetrazin-3-amines ( 16) while sequential displacement of both methylthio groups in 6 afforded the tetrazine-diamines 8 and 10 . Hydrolysis of N,N-dimethyl-6-(methylthio)-1,2,4,5-tetrazin-3-amine ( 11 ) with potassium hydroxide afforded the tetrazin-3-ol ( 12 ) which was chlorinated and then treated with 4-chlorobenzenethiol to provide 13 . The target 6-substituted-1,2,4,5-tetrazin-3-amines displayed negligible antimalarial activity.     

Synthesis of symmetrical di(pyrimidin-2-yl)-1,2,4-triazoles and di(pyrimidin-2-yl)-1,2,4,5-tetrazines

The reactions of pyrimidine-2-carbonitrile and 4,6-dimethylpyrimidine-2-carbonitrile with hydrazine hydrate were investigated. Intermediates in the route of successive transformations of pyrimidine-2-carbonitrile (pyrimidine-2-carbamidrazone and 1,2-bis[amino(pyrimidin-2-yl)methylidene]hydrazine) into trinuclear heterocyclic compounds, viz., symmetrical di(pyrimidin-2-yl)-1,4-dihydro-1,2,4,5-tetrazines and di(pyrimidin-2-yl)-4H-1,2,4-triazol-4-amines (potential polydentate ligands), were isolated. The oxidative dehydrogenation of di(pyrimidin-2-yl)-1,4-dihydro-1,2,4,5-tetrazines afforded the corresponding 3,6-di(pyrimidin-2-yl)-1,2,4,5-tetrazines.     

Synthesis of 1,2,4,5-tetrazines, symmetrically and unsymmetrically 3,6-disubstituted by N-nucleophiles

6-R-3-(3,5-Dimethylpyrazol-1-yl)-1,2,4,5-tetrazines with aliphatic, cycloaliphatic, and aromatic amines, and also with NH-heterocycles undergo a nucleophilic substitution of the dimethylpyrazole moiety yielding symmetrically and unsymmetrically substituted 1,2,4,5-tetrazines. In the 3,6-diimidazolyl-and 3,6-dibenzotriazolyl derivatives reactions of nucleophilic substitution of the heterocyclic moiety also occur. In some cases an ipsosubstitution of amino, hydrazino, and azido groups is observed.     

Cyclization of (1,2,4,5-tetrazin-3-yl)hydrazones to 3,7-dihydro-1,2,4-triazolo[4,3-b]-1,2,4,5-tetrazines

The intramolecular cyclization of (6-R-1,2,4,5-tetrazin-3-yl)hydrazones of ketones (R is 3,5-dimethylpyrazol-1-yl, 4-methylimidazol-1-yl, or 2-alkylidenehydrazino) giving rise to the previously unknown 3,7-dihydro-1,2,4-triazolo[4,3-b]-1,2,4,5-tetrazines, including spiro compounds, was studied. The reactivity and the yields of the reaction products depend on the structure of the alkylidene fragment and the nature of the substituent in the tetrazine ring.

     

Cycloaddition reactions of cyclic ketene-N,S-acetals with 1,2,4,5-tetrazines

Reaction of 3,6-diphenyl-, 3,6-bis(2-pyridyl)- and the unsubstituted 1,2,4,5-tetrazine with 4,5-dihydro-1-methyl-2-(methylthio)pyrrole ( 2 ) and 1-raethyl-2-(methylthio)-4.5,6,7-tetrahydroazepine ( 3 ) gives 4,7-di-R-2,3-dihydro-1-methylpyrrolo[2,3-d]pyridazine ( 4 , R = phenyl, 2-pyridyl, hydrogen) and 6,9-di-R-1-methyl-2,3,4,5-tetrahydropyridazino[4,5-6]azepine ( 5 ), R = phenyl, 2-pyridyl, hydrogen), respectively, in reasonable to good yields. The compounds 4 (R = phenyl, hydrogen) are converted into their corresponding 1-methylpyrrolo-[2,3-d]pyridazines 6 by reaction with potassium permanganate in butanone. Reaction of 3-phenyl-1,2,4,5-te-trazine with 2 and 3 leads to the exclusive formation of the 7-phenyl isomer 4d and 9-phenyl isomer 5d , respectively, indicating that the cycloaddition is regiospecific. The mechanism is discussed.     

Substituted pyridazines as ligands in homoleptic (fac and mer) and heteroleptic Ru(II) complexes

This article reports the preparation of a range of phenyl, pyridyl and pyrazinyl substituted pyridazines via the inverse electron demand [2 + 4] Diels-Alder reaction between 3,6-di(2-pyridyl)-1,2,4,5-tetrazines (bptz) and 3,6-di(2-pyrazinyl)-1,2,4,5-tetrazines (bpztz) and suitable dienophiles including acenaphthalene. The resulting polyaromatic compounds vary systematically in the number of aromatic substituents and the number and position of N-heteroatoms. For four of these compounds, the effect of the molecular changes on the solid-state structures were investigated using single crystal X-ray crystallography. The pyridazines were used as bidentate ligands in {M(II)(bipy)(2)} and tris(homoleptic) complexes (M = Fe, Ru). The optical and electrochemical properties of these complexes reflect the electron accepting character of the new ligands. The facial and meridional isomers of the tris complexes could be separated by column chromatography (on silica), thus allowing a spectral comparison of their absorption and emission properties. The solid-state structures of several of the metal complexes are discussed, including that of the facial isomer of the tris Ru(II) complex of 3,6-bis(2-pyridyl)-4,5-bis(4-pyridyl)pyridazine--a potential preformed geometric motif for the predirected construction of supramolecular assemblies.     

A new synthesis of 6-(alkyl)amino-3-aryl(alkyl)-1,2,4,5-tetrazines

A new method for the preparation of 6-(alkyl)amino-3-aryl(alkyl)-1,2,4,5-tetrazines is described. Dissolving 3-aryl(alkyl)-1,2,4,5-tetrazines in liquid ammonia or a primary aliphatic amine at ?35° to ?40°, followed by addition of potassium permanganate gives the title compounds in reasonable to excellent yields.     

Two-pot synthesis of N,N-disubstituted 4H-3,1-benzothiazin-2-amines from aryl(2-isothiocyanatophenyl)methanones and secondary amines

A convenient synthesis of N,N-disubstituted 4H-3,1-benzothiazin-2-amines from aryl(2-isothiocyanatophenyl)methanones using a two-pot procedure has been developed. Thus, treatment of these isothiocyanato ketones with secondary amines gave the corresponding keto thioureas, which were allowed to react with sodium borohydride or methylmagnesium bromide to afford 1,1-dialkyl-3-{2-[aryl(hydroxy)methyl]phenyl}thioureas or 1,1-dialkyl-3-[2-(1-aryl-1-hydroxyethyl)phenyl]thioureas, respectively, in one pot. Hydrobromic acid-mediated cyclization of these hydroxy thiourea precursors provided the desired 4H-3,1-benzothiazin-2-amines.     

Replacement of dimethylpyrazolyl group in 1,2,4,5-tetrazines by aliphatic alcohols and water

Reactions of 3,6-bis(4-R-3,5-dimethyl-1H-pyrazol-1-yl)-1,2,4,5-tetrazines and 3-amino-6-(3,5-dimethyl-1H-pyrazol-1-yl)-1,2,4,5-tetrazines with aliphatic alcohols and water in the presence of a base involved replacement of the dimethylpyrazolyl group and resulted in the formation of mono- and dialkoxy-1,2,4,5-tetrazines and 6-substituted 3-hydroxy-1,2,4,5-tetrazines. Dissociation constants of the latter were determined by potentiometric titration.     

Synthesis and Electrochemical Properties of 2-(4-R 1 -Phenyl)-6-(4-R 2 -phenyl)-4-phenyl-3,4-dihydro1,2,4,5-tetrazin-1(2 H )-yls

A new methodology for creating electroactive components for organic batteries, based on the construction of a molecular platform including stable 3,4-dihydro-1,2,4,5-tetrazin-1(2H)-yl radicals was described. A series of 2-(4-R1-phenyl)-6-(4-R2-phenyl)-4-phenyl-3,4-dihydro-1,2,4,5-tetrazin-1(2H)-yls with substituents of various nature was obtained. It was shown that the substituents R1 in the aromatic ring at position 2 of the tetrazinyl fragment influence the value of the oxidation potential in the radical, but do not influence the value of the reduction potentials, while the substituent R2 of the aromatic ring at position 6 influence the values of the reduction potentials and practically do not influence oxidation potential values. Based on the obtained electrochemical data, a correlation structure–potential value was revealed for the cathodic and anodic process, with the help of which triarylsubstituted 3,4-dihydro-1,2,4,5-tetrazin-1(2H)-yl radicals with high values of the electrochemical gap were obtained.     

On the composition of copper(II), cobalt(II), and nickel(II) complexes with some 3,6-disubstituted 1,2,4,5-tetrazines

Complex formation in the systems containing copper(II), cobalt(II) and nickel(II) ions (M) and 3-(3,5-dimethylpyrazol-1-yl)-6-R-1,2,4,5-tetrazines (R = 2-hydroxyethylamino, piperidino) (L) was studied by voltammetry and spectrophotometry. Cu(II), Co(II) and Ni(II) were found to form complex compounds with derivatives of 1,2,4,5-tetrazine with the ratio of the components M:L = 1:1. The complex stability constants were determined.     

Syntheses of substituted 2-(l-methyl-2-imidazolyl)quinolines

Reaction of methyllithium with 1-methy1-2-imidazolecarboxaldehyde afforded the corresponding alcohol 2. Oxidation of compound 2 with manganese dioxide gave 2-acety1-1-methylimidazole ( 3 ). Using compound 3 and substituted isatins 4 , the corresponding quinoline-4-carboxylic acids ( 5 ) were prepared. The reaction of acid imidazolides of 5 with appropriate amines yielded the amides 6 . Carbamic acid esters 10 were prepared by the Curtius rearrangement in good yield. Substituted quinolin-4-amines 13 were obtained by the acid hydrolysis of compound 10 (R₁ = t-Bu). Alkylation of amines 13 with diakylaminoalkyl chlorides gave compounds 14 .     

A novel method for the synthesis of 3,5-disubstituted-(NH)-1,2,4-triazoles from 3,6-diaryl-1,2,4,5-tetrazines

The reaction of 3,6-diaryl-1,2,4,5-tetrazines and 2-aryl substituted acetonitriles, under basic conditions, leads unexpectedly to 3,5-diaryl-(NH)-1,2,4-triazoles in moderate yields. A mechanism is proposed.     

Synthesis and reactions of 3-carbethoxy and 3-aroyl-3,4-dihydro-1h-2,3-benzoxazin-1-ones

A series of 3-substituted 3,4-dihydro-1H-2,3-benzoxazin-1-ones (IV) (Scheme I) was prepared by reaction of 2-bromomethylbenzoyl chlorides (II) with N-hydroxyethylcarbamate (III) or with benzohydroxamic acids. Acid hydrolysis of 3-carbethoxy (IVa) and 3-benzoyl derivatives (IVb) afforded a mixture of 2-(hydroxyaminomethyl)benzoic acid (V) and 2,3-dihydro-2-hydroxy-1H-1-isoindolinone (VII). Compound IVa reacted with ethanol, amines or hydrazine to yield the ethyl ester X, amides XIV (Scheme II) and the hydrazide XII of 2-(N-carbethoxy-N-hydroxy-aminomethyl)benzoic acid. Diazotization of the hydrazide XII afforded the unstable azide XIII which did not undergo the Curtius reaction but gave the benzoxazinone IVa by loss of hydrazoic acid.     

The synthesis of 5,10-dihydro- and 2,3,5,10-tetrahydrothiazolo-[3,2-b] [2,4]benzodiazepines, 1,2,3,4,7,12-hexahydrobenzothiazolo-[3,2-b] [2,4] benzodiazepine,and 9,14-dihydro-6H-[1]benzothiopyrano-[4′,3′:4,5]thiazolo[3,2-b] [2,4] benzodiazepine via 1,2,4,5-Tetrahydro-3H-2,4-benzodiazepine-3-thione

Catalytic reductive scission of phthalazine (II) utilizing a two-stage palladium-Raney nickel procedure afforded o-xylene-α,α′-diamine (III) in 97% yield. Treatment of III with carbon disulfide gave [o-(aminomethyl)benzyl]dithiocarbamic acid (IV), which upon thermal cyclization furnished 1,2,4,5-tetrahydro-3H-2,4-benzodiazepine-3-thione (V). Reaction of V with 1,2-dibromoethane, chloro-2-propanone, ethyl 2-chloroacetoacetate, ethyl chloroacetate, and ethyl 2-bromohexanoate gave 2,3,5,10-tetrahydrothiazolo[3,2-b][2,4]benzodiazepine (VII) and substituted 5,10-dihydrothiazolo[3,2-b][2,4]benzodiazepines (Villa and b, IX, and X), respectively. Condensation of V with 2-chlorocyclohexanone and 3-bromothiochroman-4-one afforded 1,2,3,4,7,12-hexahydrobenzothiazolo[3,2-b][2,4]benzodiazepine (XII) and 9,14-dihydro-6H-[1]benzothiopyrano[4′,3′:4,5]thiazolo[3,2-b][2,4]benzodiazepine(XIll). None of the compounds possessed appreciable biological activity.     

Synthesis and inverse electron demand Diels-Alder reactions of 3,6-bis(3,4-dimethoxybenzoyl)-1,2,4,5-tetrazine

The synthesis of 3,6-bis(3,4-dimethoxybenzoyl)-1,2,4,5-tetrazine (2) and the scope of its reactivity in inverse electron demand Diels-Alder reactions are disclosed representing the first systematic study of the [4 + 2] cycloaddition reactions of 3,6-diacyl-1,2,4,5-tetrazines.     

Synthesis and Spectral,Electrochemical, and Antioxidant Properties of 2-(5-Aryl-6-R-3-phenyl-5,6-dihydro-4H-1,2,4,5-tetrazin-1-yl)-1,3-benzothiazoles

Russian Journal of Organic Chemistry - New 2-(5-aryl-6-R-3-phenyl-5,6-dihydro-4H-1,2,4,5-tetrazin-1-yl)-1,3-benzothiazoles were synthesized from the corresponding formazans by alkylation and...     

Synthesis of [1,2,4]triazolo[4,3-b]-s-tetrazines with incorporated furazan ring

Furazancarboxylic hydrazides can serve as nucleophiles to substitute for one dimethylpyrazole fragment in bis(3,5-dimethylpyrazol-1-yl)-s-tetrazine, giving the corresponding N??-[6-(3,5-dimethylpyrazol-1-yl)-s-tetrazin-3-yl]-4-R-furazan-3-carbohydrazides in good yields. Dehydration of the indicated carbohydrazides in polyphosphoric acid for the first time gave rise to [1,2,4]triazolo[4,3-b]-s-tetrazines containing the furazan ring as a substituent at the triazole ring.     

Synthesis of 2,4‐disubstituted 6‐phenyl‐7H‐pyrrolo[3,2‐d]‐pyrimidin‐7‐one 5‐oxides

A relatively short and efficient method for the utilization of 4,6‐dichloro‐2‐methylthio‐5‐nitropyrimidine ( 1 ) in the synthesis of the poly substituted pyrrolo[3,2‐d]pyrimidin‐7‐one 5‐oxides ( 6a ‐g) is reported. Some new 4‐substituted 6‐chloro‐2‐methylthio‐5‐nitropyrimidines ( 2a‐e ) were prepared by reaction of 4,6‐dichloro‐2‐methylthio‐5‐nitropyrimidine ( 1 ) with amines. 4‐Substituted 2‐methylthio‐5‐nitro‐6‐phenylethynylpyrimidines ( 3a‐e ), obtained from 4‐substituted 6‐chloro‐2‐methylthio‐5‐nitropyrimidines ( 2a‐e ) via palladium‐catalyzed Sonagashira coupling reaction with 1‐phenylacetylene, underwent smooth cyclization reaction in boiling 2‐propanol in the presence of catalytic amount of pyridine to give 4‐substituted 2‐methylthio‐6‐phenyl‐7H‐pyrrolo[3,2‐d]pyrimidin‐7‐one 5‐oxides ( 4a‐e ). The methylthio group of the latter compounds can be easily and selectively oxidized by m‐chloroperbenzoic acid and replaced with different amines.     

Synthesis of thiopyrano[2,3-d] pyrimidines and thieno[2,3-d]pyrimidines

The reaction of 4-chloro-5-cyano-2-methylthiopyrimidine (I) with ethyl mercaptosuccinate (II) in refluxing ethanol containing sodium carbonate has afforded diethyl 3-amino-2-(methyl-thio)-7H-thiopyrano[2,3-d]pyrimidine-6,7-dicarboxylate (IV). Displacement of the methylthio group in IV with hydrazine gave the corresponding hydrazino derivative which underwent Schiff base formation with benzaldehyde or 2,6-dichlorobenzaldehyde. Treatment of IV in refluxing acetic anhydride afforded the corresponding diacetylated amino derivative. Partial saponification of IV with sodium hydroxide gave 5-amino-2-(methylthio)-7H-thiopyrano-[2,3-d]pyrimidine 6,7-dicarboxylic acid 6 ethyl ester (VIII). The reaction of 4-amino-6-chloro-5-cyano-2-phenylpyrirnidine (XI) with II resulted in the formation of ethyl 4-amino-6-(ethoxy-carbonyl)-5,6-dihydro-5-amino-2-phenylthieno[2,3-d]pyrimidine-6-acetate (XIII) which when subjected to hydrolysis gave ethyl 4,5-diamino-2-phenylthieno[2,3-d]pyrimidine-6-acetate isolated as the hydrochloride (XIV). Diazotization of IV with sodium nitrite in acetic acid unexpectedly afforded diethyl 5-(acetyloxy)-6,7-dihydro-6-hydroxy-2-(methylthio)-5H-thio-pyrano[2,3-d]pyrimidine-6,7-diearboxylate (XV). Several structural ambiguities were resolved by ir and pmr spectra.