Synthesis of 1,2,4-triazoles and 1,2,4-oxadiazoles

Monothiodiacylamines reacted regiosepecifically with hydrazines and hydroxylamine to give substituted 1,2,4-triazoles and 1,2,4-oxadiazoles in excellent yields.     

1,2,4-Triazines X: Dimerizations of 1,2,4-triazmes

5,5′-Bi-1,2,4-triazinyl compounds are obtained by the treatment of 5-unsubstiluted 1,2,4-triazines with either sodium methoxide or with aqueous potassium cyanide. 5,5′-Bi-1,2,4-triazinyl is also obtained by the reaction of 1,2,4-triazine with potassium cyanide. It is proposed that the sodium methoxide catalyzed dimerizations occur via a carbanionic intermediate; the aqueous potassium cyanide catalyzed reactions via a cyanide addition product and the potassium in liquid ammonia reaction via a free radical dimerization process.     

Isopolymorphie bei 1,2,4-Chlor- und 1,2,4-Bromdinitrobenzol

Ohne ZusammenfassungMit 1 AbbildungDiese Arbeit wurde im Feber 1944 bei der Zeitschrift Physikal. Chemie eingerichtet und konnte dort aus kriegsbedingten Gründen nicht erscheinen.     

1,2,4-Azadiphosphole

tert-Butylaminophosphaalkyne 4 is shown to dimerize in alkaline medium to 1-tert-butyl-3-tert-butylamino-1,2,4-azadiphosphole 1 —the first representative of 1,2,4-azadiphospholes. The structure of 1 has been determined by IR and ³¹P NMR spectroscopy and by X-ray crystallography. Compound 1 crystallizes in the triclinic space group P¯1 with a = 10.356(7), b = 11.817(5), c = 11.830(3) Å, α = 88.51(3), β = 78.61(4), γ = 77.05(4)°, V = 1383(1) ų, Z = 4 (two independent molecules).     

1,2,4-Oxadiazoles. X. Aryl-1,2,4-oxadiazolecarbaldehydes

The synthesis of 5-aryl-1,2,4-oxadiazole-3-carbaldehydes and 3-aryl-1,2,4-oxadiazole-5-carbaldehydes was attempted through several routes and achieved starting from both the corresponding chloromcthyl and the dichloromethyl derivatives. These aldehydes are stabilized in the hydrated form and this peculiar behavior is discussed on the basis of the relevant spectroscopic data.     

Synthesis of amino-1,2,4-triazoles by reductive ANRORC rearrangements of 1,2,4-oxadiazoles

The reaction of various 1,2,4-oxadiazoles with an excess of hydrazine in DMF has been investigated. 3-Amino-1,2,4-triazoles are produced through a reductive ANRORC pathway consisting of the addition of hydrazine to the 1,2,4-oxadiazole followed by ring-opening, ring-closure, and final reduction of the 3-hydroxylamino-1,2,4-triazole intermediate. The general applicability of 1,2,4-oxadiazoles ANRORC reactivity is demonstrated also in the absence of C(5)-linked electron-withdrawing groups.     

SYNTHESES AND REACTIVITY OF SOME 1,2,4-THIADIAZOLOAZINES AND 1,2,4-THIADIAZOLOAZOLES

Abstract

Recently, we have prepared a number of N-ethoxycarbonyl-N′-(2-azinyl)thioureas, which could be cyclized by oxidation into derivatives of 1,2,4-thiadiazolo/2,3-a/azines.     

The preparation of 1,2,4-Triazines and 1,2,4-Triazolines from substituted carboxamide hydrazones

Substituted carboxamide hydrazones have been condensed with 2,3-butanedione and with glyoxal to form 1,2,4-triazines; with benzaldehyde and pyridine-2-carboxaldehyde to yield 1,2,4-triazolines.     

Synthesis of 1,2,4-trioxepanes and 1,2,4-trioxocanes via photooxygenation of homoallylic alcohols

Homoallylic alcohols 4a-d, easily accessible in two steps from cyclopropyl methyl ketone, underwent a highly regioselective reaction with singlet oxygen to yield gamma-hydroxyhydroperoxides 5a-d in 57-72% yield. Acid-catalyzed reaction of 5a-d with acetone, cyclopentanone, and cyclohexanone furnished 1,2,4-trioxepanes 8a-d, 9a-d, and 10a-d in good yields. Homoallylic alcohol 12 also underwent a highly regioselective photooxygenation to yield gamma-hydroxyhydroperoxide 13 in 67% yield, which on reaction with acetone, cyclopentanone, and cyclohexanone, furnished 1,2,4-trioxocanes 16-18 in 41-55% yield.     

Mass spectra of 1,2,4-triazoles—II: Alkyl 1,2,4-triazoles

The mass spectra of monomethyl 1,2,4-triazoles contain fragment ions produced by specific cleavage of the heterocyclic ring. A major fragmentation from many molecular ions involves the elimination of HCN, but loss of N₂ is either very small or completely absent. No N or H scrambling occurs within the triazole ring system, as evidenced by labelling studies. The loss of a hydrogen atom from the molecular ions of 3-alkyl-1,2,4-triazoles (alkyl ? C₂H₅) originates from hydrogens attached to the β carbon and nitrogen atoms.     

Synthesis of triterpenoid-based 1,2,4-trioxolanes and 1,2,4-dioxazolidines by ozonolysis of allobetulin derivatives

Oxidation of allobetulin derivatives with ozone results in good isolated yields of 1,2,4-trioxolanes and stable 1,2,4-dioxazolidines. Individual 3R,5R and 3S,5S diastereoisomers of allobetulin secondary ozonides were isolated and their structures confirmed by X-ray crystallographic analysis. Remarkable diastereoselectivity with formation of only the (3S,5S)-configured peroxides was observed during the oxidation of 1,5-di-O-methoxyoximinoallobetulin to dioxazolidines.     

Construction of Coplanar Bicyclic Backbones for 1,2,4-Triazole-1,2,4-Oxadiazole-Derived Energetic Materials

Combining different nitrogen-rich heterocycles into a molecule can fine-tune its energetic performance and physical properties as well as its safety for use in energetic materials. Here, 1,2,4-oxadiazole was incorporated into 1,2,4-triazole to construct new energetic backbones. 3-(5-Amino-1H-1,2,4-triazol-3-yl)-1,2,4-oxadiazol-5-amine ( 5 ) was designed and synthesized. Nitramino-functionalized N-(5-(5-amino-1,2,4-oxadiazol-3-yl)-3H-1,2,4-triazol-3-yl)nitramide ( 6 ) and N-(5-(5-(nitramino)-1,2,4-oxadiazol-3-yl)-3H-1,2,4-triazol-3-yl)nitramide ( 7 ) were also obtained, and two series of corresponding nitrogen-rich salts were prepared, leading to the creation of new energetic compounds. All derivatives were fully characterized, and five of them were further confirmed by X-ray diffraction. The theoretical calculations, energetic performance, safety, and the main decomposition gaseous products of 1,2,4-triazole-1,2,4-oxadiazole-derived energetic materials were studied. Compound 7 and its dihydroxylammonium salt ( 7 c ) exhibited prominent detonation performance comparable to that of RDX while possessing satisfying thermal stabilities and mechanical sensitivities.     

Synthesis of fluorinated 1,2,4-oxadiazin-6-ones through ANRORC rearrangement of 1,2,4-oxadiazoles

The reaction of 3-ethoxycarbonyl-5-perfluoroalkyl-1,2,4-oxadiazoles with hydroxylamines has been investigated, evidencing the possibility of competitive reaction paths. Nucleophilic addition of hydroxylamine to the electrophilic C(5) of the 1,2,4-oxadiazole ring, followed by ring-opening and ring-closure with enlargement, leads to high yield and in very mild experimental conditions to the formation of 5-hydroxyamino-3-perfluoroalkyl-6H-1,2,4-oxadiazin-6-ones, one of these presenting water gelation ability. In turn, reactions with N-methylhydroxylamine lead the exclusive formation of 4-perfluoroacylamino-2-methyl-2H-1,2,5-oxadiazol-3-ones through the well known Boulton-Katritzky rearrangement.     

3,5-Disubstituted-1,2,4-oxadiazoles and 4,5-dihydro-3,5-disubstituted-1,2,4-oxadiazoles

A series of 3,5-disubstituted-1,2,4-oxadiazoles ( 2 ) were prepared from a mono- or dichlorophenyl-substituted amidoxime and (i) an acid chloride, (ii) an isatoic anhydride, or (iii) a β-keto ester. Although cyclizations of the same amidoximes with acetaldehyde gave 4,5-dihydro-5-methyl-substituted derivatives ( 5 ), that annulation procedure either failed or gave low yields with other aldehydes. A novel alternative method, the diborane reduction of 2 , has been found to be a generally applicable procedure for preparing 5 . The reduction is regioselective, i.e., only the 4,5-(C=N) linkage is reduced even when a large excess of diborane is present.     

Design,Synthesis and Anticancer Activity of 1,2,4-Thiadiazole Derivatives Bearing 1,2,4-Oxadiazole

Russian Journal of General Chemistry - A series of novel 1,2,4-thiadiazole derivatives bearing 1,2,4-oxadiazole is synthesized. Structures of the synthesized compounds are confirmed by 1H and 13C...     

Synthesis of 1,2,4-triazole dendrimers

A convergent synthetic strategy towards novel 1,2,4-triazole dendrimers, in which 3,5-dichloro-4-(4-methoxyphenyl)-4H-1,2,4-triazole was used as the heterocyclic building block, was successfully explored. Nucleophilic aromatic substitution at this novel AB₂-monomer was used as the key step in the propagation of the heterocyclic dendrons and these dendrons were attached to both a 1,3,5-triazine and a methylene core. The peripheral 1,2,4-triazole could be varied not only by nucleophilic aromatic substitution but also by Suzuki cross-coupling. The presented dendrimers are promising candidates to be used in applications where the large number of heteroatoms can be exploited or a better resistance to the applied conditions is required.