Regioselective cross-coupling reactions and nucleophilic aromatic substitutions on a 5,7-dichloropyrido[4,3-d]pyrimidine scaffold

The synthesis of a 5,7-dichloropyrido[4,3-d]pyrimidine scaffold is described. The chlorine at position 5 can selectively be displaced by different palladium-catalyzed cross-coupling reactions and nucleophilic aromatic substitutions. In the subsequent step, the chlorine at position 7 can be further derivatized. The described synthetic sequence allows for the construction of a diverse pyrido[4,3-d]pyrimidine library with structural variations at positions 5 and 7.     

Mass spectrometric investigation of some [1]benzopyrano[3,4-c]pyrazole and [1]benzopyrano[4,3-d]isoxazole derivatives

The fragmentation behaviour of some [1]benzopyrano[3,4-c]pyrazole and [1]benzopyrano[4,3-d]isoxazole derivatives under electron impact is described.     

The reaction of tetrahydrochromeno[3,4-c]pyridines with activated alkynes. The first synthesis of tetrahydrochromeno[4,3-d]azocines

The first synthesis of tetrahydrochromeno[4,3-d]azocines via an alkyne-induced expansion reaction is described.     

A new strategy for the synthesis of pyrazolo[4,3-e][1,2,4]triazolo[4,3-c]pyrimidines and pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidines

A series of pyrazolo[4,3-e][1,2,4]triazolo[4,3-c]pyrimidines were prepared via oxidative cyclization of aldehyde N-(1,3-diphenylpyrazolo[3,4-d]pyrimidin-4-yl)hydrazones. Dimroth rearrangement of such a series yielded pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidines.     

Catalyst-free 1,3-dipolar cycloaddition of 3-nitrochromen with sodium azide: a facile method for the synthesis of 4-aryl-1,4-dihydrochromeno[4,3-d][1,2,3]triazole derivatives

1,3-Dipolar cycloaddition of 3-nitrochromen with sodium azide under catalyst-free conditions afforded 4-aryl-1,4-dihydrochromeno[4,3-d][1,2,3]triazole derivatives at 80 °C in DMSO is described. The generality of this reaction was demonstrated by synthesizing an array of 4-aryl-1,4-dihydrochromeno[4,3-d][1,2,3]triazole derivatives. Clean reaction conditions, easy isolation, and good yields of the triazoles are the salient features of the methodology.     

Fused pyrimidine systems: XIII. Synthesis and some transformations of 1,3-thiazolo(thiazino)-fused pyrido[3,4-d]pyrimidines

2-[Allyl(propargyl)sulfanyl]pyrido[3,4-d]pyrimidin-4-ones at heating in polyphosphoric acid undergo an intramolecular cyclization with the formation of pyrido[4,3-e]thiazolo-[3,2-a]pyrimidin-5-ones of angular structure. Under similar conditions the cyclization of 2-(cinnamylsulfanyl)pyrido[3,4-d]-pyrimidin-4-one results in a linear pyrido[3′,4′:4,5]pyrimido-[2,1-b][1,3]thiazin-6-one. The iodocyclization of the same substrates affords the corresponding 9-(iodomethyl)(iodomethylidene)pyrido[4,3-e][1,3]thiazolo-[3,2-a]pyrimidin-5-ones and 3-iodopyrido[3′,4′:4,5]pyrimido[2,1-b][1,3]thiazin-6-one of angular structure. 9-(Iodomethyl)-8,9-dihydro-5H-pyrido[4,3-e][1,3]thiazolo[3,2-a]pyrimidin-5-one treated with sodium azide gave 9-(azidomethyl) derivative whose cyclization with substituted alkynes in the presence of copper compounds provided pyrido [4,3-e][1,3]thiazolo[3,2-a]pyrimidinylmethyltriazoles.     

Synthesis of some N-heteroaromatic analogues of cannabinoids

The synthesis of some [1]benzopyrano[3,4-b]pyrazine, -[3,4-d]imidazole, -[4,3-c]imidazole, -[4,3-c]pyrazole and -[3,4-d]isoxazole analogues of cannabinoids is reported.     

Tandem reactions of 6-phenylethynylpyrimidine-5-carbaldehydes with alcohols: regioselective synthesis of 5-alkoxy-(7Z)-7-benzylidene-5,7-dihydrofuro[3,4-d]pyrimidines and 5-alkoxy-7-phenyl-5H-pyrano[4,3-d]pyrimidines

An efficient and versatile tandem processes of acetalisation and cycloisomerization reactions have been developed for the reactions of 6-phenylethynylpyrimidine-5-carbaldehydes. The influence of the catalyst and role of the substituent in the position 4 of the pyrimidine ring have been studied. Regioselective synthesis of 5,7-dihydrofuro[3,4-d]pyrimidine and pyrano[4,3-d]pyrimidine cores is described.     

Synthesis of pyrazolo[4,3-e][1,2,4]triazolo[4,3-c]pyrimidines

Starting from 1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-ones, a synthesis pathway to the tricyclic pyrazolo[4,3-e][1,2,4]triazolo[4,3-c]pyrimidines is described. Reaction of 1,5-dihydro-4H-pyrazolo[3,4-d] pyrimidin-4-ones with phosphoryl chloride afforded the corresponding 4-chloro-1H-pyrazolo[3,4-d]pyrimidines. Treatment of these compounds with hydrazine hydrate at reflux temperature gave the hydrazino derivatives, which were subsequently cyclized to the titled compounds on heating with orthoesters in ethanol.     

Chemistry of 1,2,3-thiadiazole. IV. Synthesis of [1]benzoxepino-[3,4-d][1,2,3]thiadiazole, [1]benzothiepino-[3,4-d][1,2,3]thiadiazole, [1]benzoxepino[4,3-d][1,2,3]thiadiazole, [1]benzoxepino[4,3-d]oxazole and [1]benzoxepino[4,3-d]oxazole. Four novel heterocycles

Starting from the readily available 4-bromomethy-5-carbethoxy 1,2,3-thiadiazole (V), 5-bromomethy-4-carbethoxy-1,2,3-thiadiazole (IX) and ethyl 2-aryl-5-bromomethyloxazole-4-carboxylate (XIV), 4,10-dihydro-10-oxo[1]benzoxepino[3,4-d][1,2,3]thiadiazole (Ia), 4,10-dihydro-10-oxo[1]benzothiepino[3,4-d][1,2,3]thiadiazole (Ib), 4,10-dihydro-4-oxo[1]benzothiepino[4,3-d] [1,2,3]thiazole (II), 2-aryl-4,10-dihydro-4-oxo[1]benzoxepino[4,3-d]oxazoles (XIXa-XIXc) and 2-aryl-4,10-dihydro-4-oxo[1]benzothiepino[4,3-d]oxazoles (XIXd-XIXf) were prepared.     

Pyrazoles as building blocks in heterocyclic synthesis: Synthesis of pyrazolo [3,4-d]pyrimidine, pyrazolo[3,4-e][1,4]diazepine, pyrazolo [3,4-d][1,2,3]triazine and pyrolo [4,3-e][1,2,4]triazolo[1,5-c]pyrimidine derivatives

Several new pyrazolo[3,4-d]pyrimidine, pyrazolo[3,4-e][1,4]diazepine, pyrazolo[3,4-d][1,2,3]triazine and pyrolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine derivatives were prepared by the reaction of the corresponding 5-amino-pyrazole-4-carbonitrile derivative with different organic reagents under different reaction conditions. Using IR, ¹H NMR, and mass spectra we have characterized all new compounds.     

The synthesis and transformations of 9H-imidazo[1,2-b]pyrazolo[4,3-d]-pyridazine and 9H-pyrazolo[4,3-d]-s-triazolo[4,3-b]pyridazine derivatives

The nucleophilic and electrophilic substitutions of 6-substituted 9,9-dimethyl-9H-imidazo[1,2-b]pyrazolo- [4,3-d]pyridazines 2 , nucleophilic substitutions of 6-substituted 9,9-dimethyl-9H-pyrazolo[4,3-d]-s-triazolo- [4,3-b]pyridazines 7 and some other transformations to give compounds 3 and 8 , respectively, were studied. It was shown that both heterocyclic systems are stable under the conditions employed in these transformations.     

Derivatives of the new ring system pyrazolo[4,3-d]-v-triazine and the synthesis of 5,7-disubstituted 3-methylpyrazolo[4,3-d] pyrimidines and 5,7-disubstituted 3-methylpyrazolo[4,3-d]pyrimidine 6-uxides which are structurally related to the nucleoside antibiotics formycin and formycin B

The synthesis of 7-methylpyrazolo[4,3-d]-v-triazin-4-one ( 6 ), a derivative of the new ring system, pyrazolo[4,3-d]-v-triazine, has been accomplished by a diazotization reaction. Ring closure of the appropriate pyrazole derivative and oxidation of the preformed bicyclic heterocycle with m-chloroperoxybenzoic acid has furnished 7-substituted 3-methylpyrazolo[4,3-d]pyrimidine 6-oxides. Ring closures to yield various 5,7-disubstituted 3-methylpyrazolo[4,3-d]pyrimidines are also discussed.     

Synthesis of pyrazolo[4,3-<Emphasis Type="Italic">e</Emphasis>][1,2,4]triazolo[4,3-<Emphasis Type="Italic">c</Emphasis>]pyrimidines

Starting from 1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-ones, a synthesis pathway to the tricyclic pyrazolo[4,3-e][1,2,4]triazolo[4,3-c]pyrimidines is described. Reaction of 1,5-dihydro-4H-pyrazolo[3,4-d] pyrimidin-4-ones with phosphoryl chloride afforded the corresponding 4-chloro-1H-pyrazolo[3,4-d]pyrimidines. Treatment of these compounds with hydrazine hydrate at reflux temperature gave the hydrazino derivatives, which were subsequently cyclized to the titled compounds on heating with orthoesters in ethanol. Correspondence: Abolghasem Davoodnia, Department of Chemistry, School of Sciences, Islamic Azad University, Mashhad Branch, Mashhad 91735-413, Iran.     

Iodocyclization of 6-allylamino-4,5-dihydropyrazolo[3,4-d]pyrimidines

6-Allylamino-1-R-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidines treated with iodine in the presence of potassium carbonate are converted into 6-allylamino-1-R-1H-pyrazolo[3,4-d]pyrimidines that at further reaction with iodine undergo the cyclization into 6-iodomethyl-1-R-1,6,7,8-tetrahydroimidazo [1,2-a]pyrazolo[3,4-d]-pyrimidin-5-ium iodide of a linear structure. In the absence of potassium carbonate alongside the mentioned linear products 8-iodo-methyl-1-R-1,4,5,6,7,8-hexahydroimidazo[1,2-a]pyrazolo[4,3-e] pyrimidin-9-ium iodides of an angular structure have been obtained.     

Microwave-assisted multicomponent reaction of aryl amidines: regiospecific synthesis of new polysubstituted thiopyrano-, and pyrano[4,3-d]pyrimidines

A series of new functionalized thiopyrano-, pyrano[4,3-d]pyrimidine derivatives with benzyl group residing in 8-position of fused pyrimidine nucleus were synthesized through multicomponent reactions of aromatic aldehydes, tetrahydrothiopyran-4-one(tetrahydropyran-4-one), and aryl amidines using t-BuOK as a base under microwave heating. The procedure is facile, avoiding time-consuming and costly syntheses, tedious work-up, and purifications of precursors as well as protection/deprotection of functional groups. This method is very efficient due to short reaction times and easy work up and provides a four-component strategy for the construction of the thiopyrano-, and pyrano[4,3-d] pyrimidine skeletons.     

Über 4-Ureidooctahydropyrano[4,3-d]pyrimidinone

Zusammenfassung 5,6-Dihydro-2H-pyran-3-aldehyde reagieren mit Harnstoff zu 4-ureidooctahydropyrano[4,3-d]pyrimidin-2-ones. Einwirkung von Säure führt das 4-Ureidooctahydropyrano[4,3-d]pyrimidin-2-on in das 4-(2-Hydroxyäthyl)-hexahydropyrimido[4,5-d]pyrimidin-2,7-dion über.

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Heterocycles, XVIII: 4-Ureido-octahydropyrano[4,3-d]-pyrimidinones

5,6-Dihydro-2H-pyran-3-aldehydes react with urea to give 4-ureidooctahydropyrano[4,3-d]pyrimidin-2-ones. 4-Ureidooctahydropyrano[4,3-d]pyrimidin-2-one is cleaved by HCl to 4-(2-hydroxyethyl)-hexahydropyrimido[4,5-d]pyrimidin-2,7-dione.

     

Synthesis of tricyclic and tetracyclic thieno[3,2-f]-1,4-thiazepines

Treatment of 5-methylthio-2,3-dihydrothieno[3,2-f]-1,4-thiazepine ( 9 ) with acylhydrazines gave 5,6-dihydrothieno[3,2-f]-1,2,4-triazolo[4,3-d][1,4]thiazepines 10, 11 , and that of 9 with ethyl anthranilate gave 5,6-dihydrothieno[3′,2′:6,7][1,4]thiazepino[5,4-b]quinazolin-8-one ( 14 ). Reaction of 9 with hydrazine hydrate or 4-chlorophenylhydrazine afforded 5-hydrazino compounds 12, 15 , which were subsequently cyclized to ethyl 5,6-dihydrothieno[3,2-f]-1,2,4-triazolo[4,3-d][1,4]thiazepine-3-carboxylate ( 13 ), 2-(4-chlorophenyl)-5,6-dihydrothieno[3,2-f]-1,2,4-triazolo[4,3-d][1,4]thiazepin-3(2H)-one ( 16 ) and 2-(4-chlorophenyl)-6,7-dihydro-2H-thieno[3,2-f][1,2,4]triazino[4,3-d][1,4]thiazepine-3,4-dione ( 17 ). New thieno-anellated heterocycles were prepared with the aim of studying their affinity for the benzodiazepine receptors.     

Stereoselective synthesis of dihydrothiadiazinoazines and dihydrothiadiazinoazoles and their pyrolytic desulfurization ring contraction

Intramolecular base catalyzed C-C bond formation led to exclusive stereoselective syntheses of trans-6,7-dihydro-5H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines, trans-7,8-dihydro-6H-[1,2,4]triazino[3,4-b][1,3,4]thiadiazin-4-ones, and trans-3,4-dihydro-2H-[1,3,4]thiadiazino[2,3-b]quinazolin-10-one. trans-6,7-Dihydro-5H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines isomerize slowly in CDCl₃ and more rapidly in DMSO-d₆ into the corresponding cis-stereoisomers. The other trans-6,7-dihydro-[1,3,4]thiadiazines isomerize also in DMSO-d₆ into the corresponding cis-stereoisomers. Pyrolytic conversion of these heterocyclic condensed dihydrothiadiazines into their corresponding pyrazolo[5,1-b][1,2,4]triazoles, pyrazolo[5,1-c][1,2,4]triazin-4-ones and pyrazolo[4,3-b]quinazolin-9-ones via desulfurization ring contraction is described.     

Unexpected valence bond isomerization of [1,2,4]triazolo[3,4-c][1,2,4]benzotriazines under flash vacuum pyrolytic (fvp) conditions

Flash vacuum pyrolysis (fvp) of some substituted [1,2,4]triazolo[3,4-c][1,2,4]benzotriazine derivatives (1a-d) has been studied between 450 and 600 °C. The only transformation observed up to 525 °C was the unexpected valence bond isomerization of the angularly fused starting compounds to the isomeric linearly fused [1,2,4]triazolo[4,3-b][1,2,4]benzotriazine derivatives (9a-d), whereas at higher temperatures fragmentation products such as aromatic nitriles were also formed. Kinetic measurements revealed negative entropies of activation in the isomerization process, which suggest a concerted ring closure reaction to an intermediate antiaromatic diazirine. Reversibiblity of the title isomerization reaction was also proved by FVP experiments.