[1,2,3]Triazolo[1,5-a]pyridines. A theoretical (DFT) study of the ring-chain isomerization

The ring opening isomerization of [1,2,3]triazolo[1,5-a]pyridines to the corresponding 2-pyridyl derivatives has been studied by means of DFT calculations at the B3LYP/6-31+G(d,p) computational level. The effect of the substitution as well as those of protonation, deprotonation, and lithiation on different positions has been studied. The electronic characteristics of the optimized structures have been analyzed by means of the Atoms In Molecules (AIM), Electron Localization Function (ELF), Molecular Electrostatic Potential (MEP), and Natural Bond Orbital (NBO) methodologies.     

Synthesis and crystal structure of piperidinium 2-aryl[1,2,4]triazolo[1,5-a]pyridinides and their neutralization to 2-aryl[1,2,4]triazolo[1,5-a]pyridines

A one step synthesis of novel piperidinium 2-aryl[1,2,4]triazolo[1,5-a]pyridinides 6 from 2′-benzoyl-2-cyanoacetohydrazide (2) and α-substituted cinnamonitriles 3 is described. The reaction takes place by 6-exodig cyclization followed by an 5-exo-trig process to afford salts 6 . The X-ray diffraction of compound 6a reveal that the cation is strongly linked to the anion by hydrogen bonds and a characteristic partial stacking motive. 2-Aryl[1,2,4]triazolo[1,5-a]pyridines were obtained from salts 6 by treatment with hydrochloric acid.     

A study of some octahydroimidazo[1,5-a] pyridines. A new example of ring-chain tautomerism

A series of 3-substituted octahydroimidazo[1,5-a]pyridines has been prepared. An nmr study at several temperatures showed that 3-phenyloctahydroimidazo[1,5-a] pyridine (XIII) and 3-t-butyloctahydroimidazo[1,5-a] pyridine (XIV) exhibited ring-chain tautomerism. The n-propyl (X), isopropyl (XI) and benzyl (XII) derivatives did not show this form of isomerism. It has also been shown that Crabb and Newton's statement (3) that Freed and Day (1) had failed to obtain the parent compound, octahydroimidazo[1,5-a]pyridine (1), is incorrect.     

2-aryl(hetaryl)-4H-[1,2,4]triazolo[1,5-a]benzimidazoles

2-(4-Methylphenyl)-4H-[1,2,4]triazolo[1,5-a]benzimidazole and its previously unknown 2-(2-furyl)- and 2-(2-thienyl)-substituted analogs were synthesized by cyclization of benzimidazole-1,2-diamine with the corresponding carboxylic acid chlorides. The IR, ¹H, ¹³C, and ¹⁵N NMR, and mass spectra of the cyclization products in combination with the results of quantum-chemical calculations of NMR chemical shifts showed radical differences of [1,2,4]triazolo[1,5-a]benzimidazoles having no substituent on N⁴ from the recently reported low-melting products of oxidation of 2-amino-1-arylmethylideneaminobenzimidazoles with (diacetoxy-λ³-iodanyl)benzene, which, as we believe, were erroneously assigned analogous structure.     

Novel synthesis of C-3-(hetero)aryl [1,2,3]triazolo[1,5-a]pyridines using the Stille reaction

Herein, we report a novel and high yielding approach for the preparation of the first C-3-organometallic substituted [1,2,3]triazolo[1,5-a]pyridine and its application to the Stille reaction using MAOS.     

Synthesis of New 3-(Alkylsulfanyl)pyrano[3,4-c]-[1,2,4]triazolo[4,3-a]pyridines

Russian Journal of Organic Chemistry - A new method has been developed for the synthesis of 8-hydrazinylpyrano[3,4-c]pyridines via pyridine ring rearrangement. New...     

New methods for the synthesis of substituted 4,5,6,7-tetrahydro[1,2,3]triazolo[1,5-a]pyrazines (microreview)

Chemistry of Heterocyclic Compounds - The microreview summarizes the data on the methods of heterocyclization leading to the formation of the 4,5,6,7-tetrahydro[1,2,3]triazolo[1,5-a]pyrazine system...     

Acid-catalyzed reactions of 3-(hydroxymethyl)- and 3-(1-hydroxyethyl)pyrazolo[1,5-a]pyridines

Treatment of 3-(hydroxymethyl)pyrazolo[1,5-a]pyridines with trifluoroacetic acid in refluxing dichloro-methane led to the formation of bis(pyrazolo[1,5-a]pyrid-3-yl)methanes or bis[(pyrazolo[1,5-a]pyrid-3-yl)]-methyl ethers depending upon the concentration of trifluoroacetic acid. In contrast, similar treatment of 3-(1-hydroxyethyl)pyrazolo[1,5-a]pyridines gave a mixture of 3-vinylpyrazolo[1,5-a]pyridines and 1,3-bis(pyrazolo-[1,5-a]pyrid-3-yl)-1-butenes.     

1,2,4-Triazoles. XXV. The effect of pyridine substitution on the isomerization of s-Triazolo[4,3-a] pyridines into s-Triazolo[1,5-a] pyridines

The isomerization of s-triazolo[4,3-a]pyridines into s-triazolo[1,5-a]pyridines is greatly facilitated by electron withdrawing nitro substituents in the pyridine ring and retarded by electron donating amino groups.     

Triazolopyridines. Part 8.1 Nucleophilic substitution reactions of 5-bromo[1,2,3]triazolo[5,1-a]isoquinoline and 7-bromo[1,2,3]-triazolo[1,5-a]pyridine

Nucleophilic substitution of 5-bromotriazoloisoquinoline (3) and of 7-bromo-3-methyltriazolopyridine (6) proceeds readily to give a range of 5-substituted triazoloisoquinolines (4a)-(4e), and of 7-substituted triazolopyridines (7a)-(7h) respectively. Triazoloisoquinolines have been converted into 1,3-disubstituted isoquinolines (11)-(13), (15), and (16), and triazolopyridines into 2,6-disubstituted pyridines (17)-(19). Of secondary amine nucleophiles, only piperidine reacted with 7-bromo-3-methyltriazolopyridine (6) to give the 7-substituted derivative (7g). A second product in this reaction was a 2,6-disubstituted pyridine (8); the similar compounds (20)-(24) were the only products when morpholine or N-acetylpiperazine were used. The reaction between 7-bromotriazolopyridine (9) and piperidine or morpholine gave in high yield the 2,6-disubstituted pyridines (25) and (26).     

Acid-catalyzed reactions of 3-(α-hydroxybenzyl)pyrazolo[1,5-a]pyridines

Treatment of 3-(or-hydroxybenzyl)pyrazolo[1,5-a]pyridines with trifluoroacetic acid in dichloromethane resulted in the formation of pyrazolo[1,5-a]pyridines, bis[α-(pyrazolo[1,5-a]pyrid-3-yl)benzyl] ethers, and phenylbis(pyrazolo[1,5-a]pyrid-3-yl)methanes, depending upon the presence or absence of the substituents at the 2- and/or 4-positions and the reaction conditions employed.     

Characterization of copper(II) coordination compounds of 5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine: the crystal structure of diaquatetrakis(5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine-N3)-copper(II) hexafluorophosphate

Copper(II) coordination compounds of several CuA₂ salts (A = PF₆, BF₄, ClO₄, CF₃SO₃ or NO₃) with 5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine (dmtp) as a ligand have been studied. The crystal structure of [Cu(dmtp)₄(H₂O)₂](PF₆)₂ is described. This compound is monoclinic, space group P2₁/c, a = 11.826(2) Å, b = 9.463(2) Å, c = 17.673(3) Å, β = 97.50(1)°, Z = 2, d_calc. = 1.66 Mg m⁻³, and has been refined to a final discrepancy factor (R) of 0.0382 based on 2316 reflections. The structure consists of PF⁻₆ anions and centrosymmetric mononuclear [Cu(dmtp)₄(H₂O)₂]²⁺ cations, Cu₂₊ being coordinated by four equatorial N(3)-bonded dmtp molecules with CuN = 2.019 and 2.050 Å, and by two axial water molecules with CuO = 2.650 Å. The water molecules form intramolecular hydrogen bonds with the dmtp N(4) atoms.     

Acid-catalyzed reaction of pyrazolo[1,5-a]pyridines with aldehydes: Formation of bis(pyrazolo[1,5-a]pyrid-3-yl)methane

Reaction of pyrazolo[1,5-a]pyridines with aldehydes in the presence of trifluoroacetic acid gave bis[pyrazolo[1,5-a]pyrid-3-yl)methanes in high yields.