Mass spectra of some 1,2,4-thiadiazoles

Substituted 1,2,4-thiadiazoles were found to undergo fragmentation by loss of RCN from the molecular ion with both 3- and 5-substituents being involved to some extent. This was followed by loss of sulfur to yield a nitrilium ion. With 5-hydrazino substituents, hydrogen transfer was observed from the substituent to a ring nitrogen atom.     

Selenium heterocycles. XLIII. Syntheses of 3,5-Diaryl-1,2,4-thiadiazoles and 3,5-Diaryl-1,2,4-selenadiazoles

Starting from readily available α-arylsulfonyl-α-bromoacetophenones 2 a series of 3,5-diaryl-1,2,4-thiadiazoles and 3,5-diaryl-1,2,4-selenadiazoles were prepared in moderate yield. Reaction of compounds 2 with thiourea or selenourea gave 2-amino-5-arylsulfonyl-4-phenylthiazole or selenazole in good yield.     

3,6—二芳基—1,2,4—三唑并[3,4,b]—1,3,4—噻二唑化合物的合成

３－芳基－４－氨基－５－巯基－１，２，４－三唑与芳酸在三氯氧磷的作用下合成了１０个标题化合物，通过元素分析、红外光谱、核磁共振氢谱和质谱确证了它们的结构．对反应条件作了简略的讨论．部分化合物具有较强的生物活性．     

Original ring contraction of triazine derivatives to 1,2,4-thiadiazoles

The oxidation of triazines 1 is described here. While treatment with m-CPBA or DMDO led to formation of a mixture of compounds, [TBA-OX] oxidation led exclusively to thiadiazoles 2 by ring contraction reaction.     

Amidrazones. 6 . Synthesis of 1,2,4-thiadiazoles by thermolysis of N3-thiocarbamoylamidrazone ylides

Reaction of N³-unsubstituted amidrazone ylides ( 1a and 1b ) with alkyl or aryl isothiocyanates gives N³-thiocarbamoylamidrazone ylides ( 2 ). Thermolysis of 2 gives 3-alkyl(or aryl)-5-alkyl(or aryl)amino-1,2,4-thiadiazoles ( 3a-i ).     

N-15 NMR analysis of 1,2,3-thiadiazoles

The ¹⁵N nmr spectra of a series of 1,2,3-thiadiazoles reveal the strong influence of substituents at C-5 on the N-2 resonance. Upon methylation, the two thiadiazole nitrogen resonances are shielded, but the most dramatic shift is observed for the methylated nitrogen, Δδ > 140 ppm. The ¹⁵N chemical shifts of some mesoionic thiadiazoles were also determined and explained by the dual effect of 5-substitution and salt formation. By disconnecting these effects, the ¹⁵N chemical shifts of 10 and 11 were found to be unusual and to reflect a thiapentalene character.     

Regioselectivity of Alkylation of 3-Substituted 5-Amino-1,2,4-thiadiazoles

We have synthesized 3-substituted 4-alkyl-5-imino-4,5-dihydro-1,2,4-thiadiazoles by reaction of 3-alkyl(benzyl)thio-5-amino-1,2,4-thiadiazoles with methyl iodide or ethylene chlorohydrin. In the reaction with epichlorohydrin, addition of an oxirane molecule occurs with formation of tetrahydropyrimido[2,1-b]-1,2,4-thiadiazoles.     

1,2,4-三唑并[3,4-b]-1,3,4-噻二唑的合成

近年来稠杂环化合物的合成及其生物活性的研究日益成为杂环化学研究的热门课题。3,6-二取代-1,2,4-三唑并噻二唑衍生物是具有广谱生物活性的稠杂环化合物,如抗菌、消炎、杀微生物、调节植物生长、除草等,因而引起各国化学家的广泛兴趣。此类化合物的生物活性,     

Synthesis of novel functionalized 1,2,4-thiadiazoles from 3,4-diaminofurazane and isothiocyanates

The addition of isothiocyanates to borylated 3,4-diaminofurazane is accompanied by a rearrangement to form compounds of the 1,2,4-thiadiazole series. The derivatives of 3-(5-amino-1,2,4-thiadiazole)carboxamidoxime were prepared and it was suggested to use these reagents in heterocyclic syntheses with 1,2,4-oxadiazole or a second 1,2,4-thiadiazole ring closure.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 174–176, January, 1992.     

Syntheses of substituted-oxazolo-1,3,4-thiadiazoles, 1,3,4-oxadiazoles,and 1,2,4-triazoles

Starting from readily available methyl 5-methyloxazole-4-carboxylate ( 1 ) and 4-methyl-5-oxazolylcar-boxylic acid hydrazide ( 11 ) the title compounds were prepared. The reaction of compound 1 with hydrazine hydrate afforded the corresponding hydrazide 2 . The reaction of compound 2 with formic acid yielded 1-formyl-2-(5-methyloxazole-4-carboxyl)hydrazine ( 3 ). Refluxing of the latter with phosphorus pentasulfide in xylene gave compound 5 in 62% yield. The reaction of compound 3 with phosphorus pentoxide afforded compound 4 . Starting from hydrazide 11 , compounds 13 and 14 were prepared similarly. Reaction of compound 2 with substituted isothiocyanate yielded compound 9 which was cyclized in basic medium to 4-alkyl-5-(5-methyl-4-oxazolyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione ( 10 ). The isomer 19 was prepared similarly. Methylation and subsequent oxidation of compound 19 gave compound 21 . Reaction of the acid 7 with thiosemicarbazide in the presence of phosphorus oxychloride gave 2-amino-5-(5-methyl-4-oxazolyl)1,3,4-thiadiazole ( 8 ). 2-Amino-5-(4-methyl-5-oxazolyl)-1,3,4-thiadiazole ( 17 ) was prepared from acyl chloride 15 by the usual method.     

An unexpected synthesis of 3,5-diaryl-1,2,4-thiadiazoles from thiobenzamides and methyl bromocyanoacetate

Aryl thioamides undergo very rapid condensation in the presence of methyl bromocyanoacetate to provide quantitative yields of 3,5-diaryl-1,2,4-thiadiazoles with an easy work-up and a high degree of product purity. The method can be scaled up with no loss in efficiency.     

Photochemistry of 1,2,4-oxadiazoles. A DFT study on photoinduced competitive rearrangements of 3-amino- and 3-n-methylamino-5-perfluoroalkyl-1,2,4-oxadiazoles

The photoinduced competitive rearrangements of 5-perfluoroalkyl-3-amino(N-alkylamino)-1,2,4-oxadiazoles have been investigated by DFT calculations and UV-vis spectroscopy. The observed product selectivity depends on the number of hydrogen atoms present in the amino moiety and involves two or three possible routes: (i) ring contraction-ring expansion (RCRE), (ii) internal-cyclization isomerization (ICI), or (iii) C3-N2 migration-nucleophilic attack-cyclization (MNAC). UV absorption and fluorescence spectra of the reactants, and vertical excitation energy values, calculated by time dependent DFT, support the involvement of a neutral singlet excited state in the photoexcitation process. The values of the standard free energy of the most stable prototropic tautomers of reactant, products, proposed reaction intermediates, and deprotonated anionic transition states allowed us to rationalize the competition among the three rearrangements, in agreement with chemical trapping experiments, in terms of: (i) the evolution of the excited state toward three stable ground-state intermediates, (ii) tautomeric and deprotonation equilibria occurring in methanol solution for each intermediate, and (iii) relative stabilization of intermediates and transition states in the thermally driven section of the reaction.     

IBX/TEAB-mediated oxidative dimerization of thioamides: synthesis of 3,5-disubstituted 1,2,4-thiadiazoles

Thioamides undergo oxidative dimerization on treatment with hypervalent iodine(V)-containing reagents, particularly o-iodoxybenzoic acid (IBX), in the presence of tetraethylammonium bromide (TEAB) to generate 3,5-disubstituted 1,2,4-thiadiazoles in excellent yield.     

Reactions of tetrasulfur tetranitride with bromomethyl ketones. One pot synthesis of 3,5-diaroyl- and 3,5-diacyl-1,2,4-thiadiazoles

Reactions of tetrasulfur tetranitride (S⁴N⁴) with aryl and alkyl bromomethyl ketones 1 in chlorobenzene at reflux temperature gave 3,5-diaroyl- and 3,5-diacyl-1,2,4-thiadiazoles 2 in 17-60% yields. No 1,2,5-thiadiazoles were detected. By heating of the two reactants at 115° without the solvent were also obtained 2 in 5-13% yields. Hydrolysis of 2 with sodium hydroxide in a mixture of ethanol, ethyl acetate, and water (v:v, 4:2:1) at 75° to 85° afforded the heretofore inaccessible 3-aroyl- and 3-acyl-1,2,4-thiadiazoles 3 in 17-79% yields.     

An efficient one-pot synthesis of 3-substituted-5-amino-1,2,4-thiadiazoles from isothiocyanates and amidines

An efficient one-pot synthesis of 3-substituted-5-amino-1,2,4-thiadiazoles from isothiocyanates and amidines is described.     

Preparation of novel 1,2,4-thiadiazoles by cyclization with 4-methylbenzenesulfonyl cyanide (tosyl cyanide)

The preparation of 1,2,4-thiadiazoles with a di-tert-butylphenol substituent at the thiadiazole 3-position is described. A thermally generated nitrile sulfide was reacted with tosyl cyanide in a 1,3-dipolar cyclization reaction to provide a thiadiazole intermediate containing a labile 5-tosyl substituent.