One-Step conversion of pyridine N-oxides to tetrazolo[1,5-a]pyridines

Pyridine N-oxides were converted to tetrazolo[1,5-a]pyridines in good to excellent yield by heating in the presence sulfonyl or phosphoryl azides and pyridine in the absence of solvent. Various sulfonyl and phosphoryl azides were screened for reactivity under a standard set of conditions. Diphenyl phosphorazidate was the most convenient reagent and gave high yields. Reaction optimization, scope, and scalability are discussed.     

Synthesis of new calix[4]pyrrole derivatives via 1,3-dipolar cycloadditions

Octamethylcalix[4]pyrrole-2-carbaldehyde 1 and 3-(octamethylcalix[4]pyrrol-2-yl)propenal 5 were used as precursors of azomethine ylides, which were trapped in situ with a range of dipolarophiles, such as 1,4-benzoquinone, 1,4-naphthoquinone, and fumaronitrile. Aldehyde 1 showed very low reactivity but the azomethine ylide generated from the reaction of aldehyde 5 with N-methylglycine could be trapped with those dipolarophiles to afford new β-substituted octamethylcalix[4]pyrrole derivatives in moderate yields. The resulting cycloadducts show high affinity constants for fluoride and acetate anions; compounds 7 and 8 display sharp changes in color in the presence of these anions.     

Synthesis of some 1,3-disubstituted imidazo[1,5-a]pyridines using 2-cyanopyridine

Heating 2-cyanopyridine and hydrazine hydrate at 100 °C and reheating the resultant liquid with pyridine-2-carboxaldehyde yielded a red semi-solid. On adding aqueous KOH, a mixture of 1-(3,5-bis(2-pyridyl)-1,2,4-triazolyl)-3-(2-pyridyl)imidazo[1,5-a]pyridine (2a) and 1-((2-pyridyl)methanimine)-3-(2-pyridyl)imidazo[1,5-a]pyridine (2b) precipitated and from the filtrate 3,5-bis(2-pyridyl)-1,2,4-triazole (1) was isolated. Similar compounds were obtained from two other pyridinecarboxaldehydes.     

An intramolecular one-pot synthesis of steroidal triazoles via 1,3-dipolar cycloadditions of in situ generated diazo compounds

A novel synthetic route is reported for the preparation of steroidal triazoles via intramolecular 1,3-dipolar cycloaddition of a steroidal 16,17-seco-17-diazo-16-nitrile system. The structures of the products are established by X-ray and NMR studies. The in vitro antiproliferative activity of the steroidal triazoles against three tumor cell lines was evaluated.     

Synthesis of derivatives of tetrazolo[1,5-a]- and oxazolo[4,5-b]pyrano(thiopyrano)[3,4-c]pyridines

Tetrazolo[1,5-a]- and oxazolo[4,5-b]pyrano(thiopyrano)[3,4-c]pyridines, which are new heterocyclic systems, have been synthesized from pyrano[3,4-c]pyridine derivatives.A. L. Mndzhoyan Institute of Fine Organic Chemistry, Armenian Academy of Sciences, Yerevan 375014. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1260–1262, September, 1997.     

Synthesis of pyrazolo[1,5-a][4,1]benzoxazepines via intramolecular nitrilimine cycloaddition

A synthetic route to the title compounds is described, which involves as the key step an intramolecular cycloaddition of properly functionalized nitrilimines.     

3-Substituted imidazo[1,5-a]pyridines

Cyclization of amides of 2-aminomethylpyridine gave imidazo[1,5-a]pyridines. In several examples the literature preparation (phosphorus oxychloride) gave extensive tar formation. The use of phosphorus trichloride-triethylamine (?20°) gave the desired imidazo[1,5-a]pyridines.     

Synthesis of novel pyrano[2,3-b]quinolines from simple acetanilides via intramolecular 1,3-dipolar cycloaddition

Some novel isoxazole and pyrazole fused pyrano[2,3-b]quinolines were synthesized from simple acetanilides via intramolecular 1,3-dipolar cycloaddition reactions involving nitrones, nitrile oxides and nitrile imines as 1,3-dipoles, in a regioselective manner.     

Synthesis of pyrazolo[1,5-a]pyridines and pyrazolo[1,5-c]pyrimidines by reaction of heterocyclic amidrazones with 1,3-dicarbonyl compounds

1,3-Dicarbonyl compounds 2 react with 1-amino-2(1H)-pyridin-2-imines or 1-amino-2(1H)-pyrimidin-2-imines 1 giving new pyrazolo[1,5-a]pyridines or pyrazolo[1,5-c]pyrimidines 5 respectively by addition, oxidation and condensation. Isolation of an intermediate 3 shows that surprisingly the addition of the CH acidic 1,3 -dicarbonyl compound to position 6 of the pyrimidine 1 is the initial step.     

Unprecedented intramolecular [3 + 2] cycloadditions of azido-ketenimines and azido-carbodiimides. Synthesis of indolo[1,2-a]quinazolines and tetrazolo[5,1-b]quinazolines

N-(2-azidomethyl)phenyl ketenimines and N-(2-azidomethyl)phenyl-N'-alkyl(aryl) carbodiimides undergo, under mild thermal conditions, intramolecular [3 + 2] cycloaddition reactions between the azido group and either the C=C or the distal C=N double bonds of the ketenimine and carbodiimide functions respectively. The reaction products are indolo[1,2-a]quinazolines and/or indolo[2,1-b]quinazolines in the case of azido-ketenimines, and tetrazolo[5,1-b]quinazolines in the case of azido-carbodiimides. The formation of the two classes of indoloquinazolines implies the ulterior dinitrogen extrusion from the non-isolated, putative [3 + 2] cycloadducts between the azide and ketenimine functions, whereas in the case of azido-carbodiimides the initial cycloadducts, tetrazoloquinazolines, were cleanly isolated and further converted into 2-aminoquinazolines by thermally induced dinitrogen extrusion.     

Synthesis of novel polyfunctional pyrrolo[2,1-a]isoquinolines based on 1,3-dipolar cycloaddition reactions

Russian Chemical Bulletin - A series of 5-substituted 8-nitroisoquinolines was synthesized based on the reaction of 5-bromo-8-nitroisoquinohne with various nucleophiles. N-Alkylation products of...     

Heterocycles from amino acids. A novel synthetic approach for imidazo[1,5-a]pyridines and imidazo[1,5-a]quinolines

From the corresponding heterocyclic amino acids 2 and 9a the heterocyclic systems imidazo[1,5-a]pyridine ( 3 ) and imidazo[1,5-a]quinoline ( 10 ) are easily accessible. From compound 7 the tricyclic system 11 was prepared and from compound 17a a pyridyl-1,2,4-triazinone ( 18 ) could be obtained.     

Synthesis of 2,3-Dihydroimidazo[1,2-a]pyridines from 1,3-Diketones

A series of 2-hydroxy-, 2-chloro-, and 2-(2-hydroxyethylamino)-6-aryl-4-polyfluoroalkyl-3-cyanopyridines has been synthesized. The latter react with phosphorus oxychloride to give fluorine containing 2,3-dihydroimidazo[1,2-a]pyridines.     

Mass spectral fragmentation patterns of isomeric s-Triazolo[4,3-a]pyridines and s-triazolo[1,5-a]pyridines

The major decomposition pathway involved in the fragmentation of derivatives of the title ring systems was the loss of RCN from the five-membered ring, except when this ring had a 3-amino,3-hydroxyl or 3-mercapto substituent. In these cases, the exocyclic substituent and at least one nitrogen atom from the five-membered ring were lost.     

Synthesis of triazolo[4,3-d], tetrazolo[1,5-a] -and quinazolino[3,2-d] [1,4] benzodiazepines

Treatment of 5-methylmercapto-1,4-benzodiazepine (I) with hydrazine hydrate gave the 5-hydrazino derivative (II, R = H) which, in turn, was conveniently cyclized to the title compounds. Another method for the synthesis of triazolo [4,3-d] [1,4] benzodiazepines (III) is also described.     

Direct arylation of tetrazolo[1,5-a]pyridine and its benzenologues

Diphenyliodonium fluoroborate proved to be a suitable reagent for direct arylation of bridge head nitrogen containing fused heteroaromatic systems. By this one step method, 1-aryl-tetrazolo[1,5-a]pyridinium salt (3) can be obtained. Arylation of related benzenologues gave not only 1-aryl but also 2-aryltetrazolium salts.

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Direkte Arylierung von Teterazolo[1,5-a]pyridin und dessen Benzologen (Kurze Mitteilung)

Zusammenfassung Kondensierte Heteroaromaten mit Brückenkopf-Stickstoff können direkt mit Diphenyl-Jodonium Fluoroborat aryliert werden. In dieser Weise wird 1-Aryltetrazolo[1,5-a]pyridinium Salz (3) in einer Reaktionsstufe synthetisiert. Arylierung der verwandten Benzologen führten nicht nur zu 1-Aryl, sondern auch zu 2-Aryltetrazolium Salzen.