2-R-5-Ar(Het)-5,6-dihydro-7H-[1,2,4]triazolo[5,1-b][1,3]thiazin-7-ones

A novel method for synthesis of 2-R-5-Ar(Het)-5,6-dihydro-7H-[1,2,4]triazolo[5,1-b][1,3]thiazin-7-ones by condensation of 3-R-4,5-dihydro-1H-1,2,4-triazole-5-thiones with 3-aryl(heteryl)-2-propenoyl chlorides is proposed.     

Aminolysis of 2-Aryl-5-R-5,6-dihydro-7H-[1,2,4]triazolo[5,1-<Emphasis Type="Italic">b</Emphasis>]1,3]thiazin-7-ones

We have established that the products of aminolysis of 2-aryl-5-R-5,6-dihydro-7H-[1,2,4]triazolo-[5,1-b][1,3]thiazin-7-ones in boiling ethanol are 3-R-3-(5-aryl-4H-1,2,4-triazol-3-ylsulfanyl)-propanamides, and at 180°C–210°C (depending on the structure of the substituent R): 3-phenyl-4,5-dihydro-1H-1,2,4-triazoline-5-thione and 3-arylacrylamides or 3-(3-aryl-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-1-yl)propanamides. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1587–1592, October, 2005.     

Unexpected Direction of Iodocyclization of 3-Allylthio-5-phenyl-4H-1,2,4-triazole

The reaction of 3-allylthio-5-phenyl-4H-1,2,4-triazole with iodine to give a mixture of 5,6-dihydro-5-iodomethyl-3-phenyl[1,3]thiazolo[2,3-c][1,2,4]triazole, 6,7-dihydro-6-iodo-3-phenyl-5H-[1,2,4]triazolo[3,4-b][1,3]thiazine, 5,6-dihydro-6-iodomethyl-2-phenyl[1,3]thiazolo[3,2-b][1,2,4]triazole, and 6,7-dihydro-6-iodo-2-phenyl-5H-[1,2,4]triazolo[5,1-b][1,3]thiazine has been studied. The structure of the products obtained was established using ¹H NMR spectroscopy of their dehydriodination products.     

Synthesis and Transformations of 2-R-5-Aryl-5,6-dihydro-7H-[1,2,4]-triazolo[5,1-b][1,3]thiazin-7-ones

A new procedure for preparation of 2-R-5-aryl-5,6-dihydro-7H-[1,2,4]triazolo[5,1-b][1,3]thiazin-7-ones by condensation of 5-R-1,2,4-triazole-3-thiones with 3-arylacryloyl chlorides was developed. The thiazine ring of the [1,2,4]triazolo[5,1-b][1,3]thiazin-7-ones is easily cleaved by treating with ammonia and hydrazine affording amides and hydrazides of 3-aryl-3-(1H-1,2,4-triazol-5-ylsulfanyl)propanoic acids. The latter react with isothiocyanates furnishing carbamoyl thiohydrazides of 3-aryl-3-(1H-1,2,4-triazol-5-ylsulfanyl)propanoic acids that in alkaline media undergo cyclization into 4-aryl-5-[2-(4H-1,2,4-triazol-5-ylsulfanyl)-2-phenylethyl]-2,4-dihydro-3H-1,2,4-triazole-5-thiones.     

Regioselective Synthesis of 2-Substituted [1,2,4]Triazolo[5,1-b][1,3]thiazin-7-ones by Heteropolyacids

2-Substituted [1,2,4]triazolo[5,1-b][1,3]thiazin-7-ones 3 were synthesized via regioselective cyclization of 4H-[1,2,4]triazol-3-ylsulfanyl-acrylic acids 2 in the presence of catalytic amounts of heteropolyacids at room temperature in very good yields and rates.     

Synthesis of 4-Amino-6-R-4,5-dihydro-3-phenacylthio-1,2,4-triazin-5-ones and 8H-3-R-7-Aryl-1,2,4-triazino[3,4-b][1,3,4]thiadiazin-4-ones

A study was carried out on the reaction of 4-amino-6-R-2,3,4,5-tetrahydro-3-thioxo-1,2,4-triazin-5-ones with halo ketones in alkaline media to yield 4-amino-6-R-4,5-dihydro-3-phenacylthio-1,2,4-triazin-5-ones, which then convert to 8H-3-R-7-aryl-1,2,4-triazino[3,4-b][1,3,4]thiadiazin-4-ones.     

Synthesis of 2-Aryl-2,3-dihydro-4H-[1,3]thiazino[3,2-a]benzimidazol-4-ones and 7-Aryl-2,3,6,7-tetrahydro-5H-imidazo[2,1-b]-1,3-thiazin-5-ones

The reaction of 2-mercaptobenzimidazole, 5-ethoxy-2-mercaptobenzimidazole, and 2-mercaptoimidazoline with cinnamoyl chloride, its derivatives, and heteroanalogs was studied. Convenient methods were found for the synthesis of 2-aryl-2,3-dihydro-4H-[1,3]thiazino[3,2-a]benzimidazol-4-ones and 7-aryl-2,3,6,7-tetrahydro-5H-imidazo[2,1-b]-1,3-thiazin-5-ones.     

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.     

Pyrolytic desulfurization ring contraction of condensed thiadiazines as a general route towards pyrazoloazines and pyrazoloazoles with a bridgehead (ring junction) nitrogen atom

Pyrolytic conversion of [1,2,4]triazino[3,4-b][1,3,4]thiadiazin-4-ones, [1,3,4]thiadiazino[2,3-b]quinazolin-10-ones and [1,2,4]triazolo[3,4-b][1,3,4]thiadiazines into their corresponding pyrazolo[5,1-c][1,2,4]triazin-4-ones, pyrazolo[4,3-b]quinazolin-9-ones and pyrazolo[5,1-b][1,2,4]triazoles via desulfurization ring contraction is described. The starting condensed 1,3,4-thiadiazines were prepared from the corresponding readily available 4-amino-3-thioxo-1,2,4-triazin-5(4H)-ones, 3-amino-2,3-dihydro-2-thioxoquinazolin-4(1H)-one and 4-amino-3(2H)-thioxo-1,2,4-triazoles upon reaction with the appropriate α-haloketones in two steps, or directly in one step in ethylpyridinium tetrafluoroborate (ionic liquid, IL).     

Interaction of 7-Chloro-9-methylthio-3-phenylpyrimido[5,4-f][1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine with Some Nucleophiles

The reactions of 7-chloro-9-methylthio-3-phenylpyrimido[5,4-f][1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (1) with some nucleophiles have been studied. Substitution of the chlorine atom with hydrogen occurs with ammonia in DMSO to give 9-methylthio-3-phenylpyrimido[5,4-f][1,2,4]triazolo[3,4-b][1,3,4]thiadiazepin-7(8H)-one. With a methanolic solution of ammonia the 7-methoxy derivative is formed. Reaction of compound 1 with an excess of sodium methoxide in methanol gave 6,7-dimethoxy-9-methylthio-3-phenyl-5,6-dihydropyrimido[5,4-f][1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine. The corresponding 7-substituted derivatives were obtained when compound 1 was heated with morpholine or 2-(dimethylamino)ethylamine. The azomethine bond of the thiadiazepine ring is reduced by sodium borohydride to give the corresponding 5,6-dihydro derivatives.     

Synthesis and chemical transformations of partially hydrogenated [1,2,4]triazolo[5,1-b]quinazolines

The reaction of 5-methyl-7-phenyl-4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidine with α,β-unsaturated carbonyl compounds in MeOH in the presence of MeONa affords partially hydrogenated aryl-substituted [1,2,4]triazolo[5,1-b]quinazolines. Hydrolysis, oxidation, reduction, and alkylation of 5,6,8-triphenyl-5,6,7,10-tetrahydro[1,2,4]triazolo[5,1-b]quinazoline were studied. The structure of one oxidation product, viz., 7-hydroxy-5,6,8-triphenyl-6,7-dihydro[1,2,4]triazolo[5,1-b]quinazoline, was established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 335—340, February, 2006.     

Synthesis of Substituted 5,6-Dihydro-4H-[1,2,4]triazolo[4,3-a][1,5]benzodiazepines

A one-pot synthetic approach to the novel 5,6-dihydro-4H-[1,2,4]triazolo[4,3-a][1,5]benzodiazepines by thermal cyclization of 4-acylhydrazino-2,3-dihydro-1H-1,5-benzodiazepines is described.     

Study of the Products of Iodocyclization of 4-Allyl-5-phenyl-1,2,4-triazole-3-thione

The interaction of 4-allyl-5-phenyl-1,2,4-triazole-3-thione with iodine proceeds with the formation of a mixture of 6-iodomethyl-3-phenyl-5,6-dihydrothiazolo[2,3-c]-1,2,4-triazole and 6-iodo-3-phenyl-6,7-dihydro-5H-1,2,4-triazolo[3,4-b]-1,3-thiazine. The structures of the cyclization products obtained were established on the basis of the ¹H NMR spectra of their dehydroiodinated derivatives. 6-Methyl-3-phenylthiazolo[2,3-c]-1,2,4-triazole, 3-phenyl-5H-1,2,4-triazolo[3,4-b]-1,3-thiazine, and 3-phenyl-7H-1,2,4-triazolo[3,4-b]-1,3-thiazine are formed on eliminating HI from the cyclization products.     

Cascade cyclization reactions of 3,4,5-triamino-1,2,4-triazole with aromatic aldehydes and cycloalkanones

A three-component condensation of 3,4,5-triamino-1,2,4-triazole (1) with aromatic aldehydes 2a–f and dimedone (3) or cyclohexanone (8) afforded partially hydrogenated 9-aryl-[1,2,4]triazolo[5,1-b]quinazolin-8-ones. The structure of 2-amino-6,6-dimethyl-3-(4-nitrobenzylidene)amino-9-(4-nitrophenyl)-5,6,7,9-tetrahydro[1,2,4]triazolo[5,1-b]quinazolin-8-one (4e) was confirmed by X-ray diffraction data. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1178–1182, July, 2006.     

6-Arylamino-3-methyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines: Novel N-Arylamidine Structures

We propose a method for obtaining derivatives of 7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine by alkylation of 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol by substituted -chloroacetanilides, followed by cyclization of the intermediate by phosphorus oxychloride.     

Some chemical properties of 2,3-dihydro-4H-[1,3]thiazino[3,2-a]benzimidazol-4-one and 2-aryl-2,3-dihydro-4H-[1,3]thiazino[3,2-a]benzimidazol-4-ones

We have studied the reaction of 2,3-dihydro-4H-[1,3]thiazino[3,2-a]benzimidazol-4-one and 2-aryl-2,3-dihydro-4H-[1,3]thiazino[3,2-a]benzimidazol-4-ones with amines, alkylating reagents, and hydrogen peroxide. We have shown that the presence of an aryl substituent at the 2 position of [1,3-thiazino[3,2-a]benzimidazol-4-ones has a substantial effect on the direction of the reactions. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 445–452, March, 2006.     

Sulfuric Acid: A Mild Catalyst for the Regioselective Synthesis of 2-Substituted [1,2,4]Triazolo[5,1- b ][1,3]thiazin-7-ones

 A facile and regioselective synthesis of 2-substituted [1,2,4]triazolo[5,1-b][1,3]thiazin-7-ones by action of sulfuric acid on (4H-[1,2,4]triazol-3-ylsulfanyl)-acrylic acids is described.     

Synthesis and opening of the thiadiazine ring in 6,7-dihydro-5H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines

A reaction of 3-benzylthiotriazole-4-amines with aromatic aldehydes leads to the formation of 6,7-dihydro-5H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines. A dihydrothiadiazine ring opening along the N-N bond occurs by the action of strong bases. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1249–1252, June, 2008.     

2-R-7-methyl[1,2,4]triazolo[2,3-a]pyrimidines: synthesis and structures

Reactions of 5-R-3-amino-1,2,4-triazoles with ethoxymethylideneacetylacetone and ethyl ethoxymethylideneacetoacetate proceeded regioselectively, giving 2-R-7-methyl[1,2,4]triazolo[2,3-a]-pyrimidines in good yields. The compounds obtained were characterized by elemental analysis, ¹H NMR spectroscopy, and X-ray diffraction analysis (for ethyl 2-ethylthio-7-methyl[1,2,4]triazolo[2,3-a]pyrimidine-6-carboxylate). The frontier orbitals, the molecular electrostatic potential, and the geometries of the reagent molecules were calculated by the DFT method (B3LYP/6-31G**). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1244–1248, June, 2008.     

Sulfuric Acid: A Mild Catalyst for the Regioselective Synthesis of 2-Substituted [1,2,4]Triazolo[5,1-b][1,3]thiazin-7-ones

Summary.  A facile and regioselective synthesis of 2-substituted [1,2,4]triazolo[5,1-b][1,3]thiazin-7-ones by action of sulfuric acid on (4H-[1,2,4]triazol-3-ylsulfanyl)-acrylic acids is described. Received January 23, 2001. Accepted (revised) May 7, 2001