Halocyclization of 2-allylthiopyridine

2-Allylthiopyridine reacts with iodine to form 3-iodomethyl-2,3-dihydrothiazolo[3,2-a]pyridinium triiodide, but in reaction with bromine a mixture of 3- and 2-bromomethyl-2,3-dihydrothiazolo[3,2-a]pyridinium bromides is obtained.Chelyabinsk State University, Chelyabinsk 454021; RussiaTranslated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 334–336, March, 1999.     

Thiazolo [3,2-a] pyridinium salts

The sulfides formed by the reaction of α-halo ketones or α-halo acetals with 2-mercaptopyridine may be cyclized in good yield to form thiazolo[3, 2-a]pyridinium salts. The presence of chloro or nitro substituents on the pyridine ring does not interfere with the synthesis. Nitration of 3-methylthiazolo[3, 2-a]pyridinium perchlorate has been found to occur at position 8.     

Concise and efficient synthesis of 4-fluoro-1H-pyrrolo[2,3-b]pyridine

Two routes describing the preparation of 4-fluoro-1H-pyrrolo[2,3-b]pyridine (4a) from 1H-pyrrolo[2,3-b]pyridine N-oxide (1) are presented. Regioselective fluorination was achieved using either the Balz-Schiemann reaction or lithium-halogen exchange. [reaction: see text]     

Research on heterocyclic compounds. XX. Synthesis of trifluoromethyl derivatives of fused imidazole systems

A series of heterocyclic compounds having an imidazole ring fused with another ring with a bridgehead nitrogen atom and bearing a trifluoromethyl moiety was synthesized by reaction of 3-bromo-1,1,1-trifluoroacetone with various heteroarylamines. In some cases, an intermediate compound obtained together with the required product was isolated and its structure was elucidated: e.g., starting from 2-aminopyridine we have obtained 2-trifluoromethylimidazo[1,2-a]pyridine and 2-hydroxy-2-trifluoromethyl-2,3-dihydro-1H-imidazo [1,2-a]pyridinium bromide. Such results confirmed the mechanism previously proposed for this reaction.     

Condensed pyridines. 6. Synthesis and strucutre of adamantyl-, cyclopropyl- and alkyl-substituted 3-halomethyl-2,3-dihydro-8-cyanothiazolo[3,2-a]pyridinium salts and their oxazolo and selenazolo derivatives

The reaction of substituted 2-cyanopyridin-2(1H)-ones and their thione and selenone derivatives with allyl bromide gives the corresponding 2-allyloxy-, 2-allylmercapto-, and 2-allylseleno-3-pyridines, which upon treatment with halogens, form intramolecular quaternization products, namely, 3-halomethyl-2,3-dihydro-8-cyanooxazole[3,2-a]pyridinium salts and their thiazolo and selenazolo analogs. X-ray diffraction structural analysis was used to determine the structure of 3-bromomethyl-2,3-dihydro-5,7-dimethyl-8-cyanothiazolo[3,2-a]pyridinium perchlorate.For Communication 5, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 690–700, May, 1987.     

1-Phenyl-2,3-diazacycl[3,2,2]azine,a new 10-π electron system. Involvement of 3,5-didehydroimidazo[1,5-a]pyridine?

3-Ethylthioimidazo[1,5-a]pyridine reacts with butyl lithium followed by benzonitrile to give the new 10-π electron system, 1-phenyl-2,3-diazacycl[3,2,2]azine, possibly via 3,5-didehydroimidazo[1,5-a] pyridine.     

Quantum chemical predictions concerning two unknown “mesoionic” compounds

The Pariser-Parr-Pople approximation was used to predict the properties of compounds I, 3-oxo-2H-1,2,3-triazolo[3,4-a]pyridine, and II, 3-oxoisoxazolo[2,3-a]pyridine, originated by joining a pyridine ring to two sydnone-like heterocyclic systems not yet reported in the literature. A parallel computation was carried out for two known compounds of similar structure, to give the predictions a better reliability through the comparison with observed spectral data and chemical behaviour. Compound I is expected to be stable, with an absorption spectrum similar to III, 2-oxo-1,3,4-oxadiazolo[4,5-a]pyridine, and chemical properties analogous to IV, 1-methyl-3-oxo-1,2,4-triazolo-[4,3-a]pyridine. A reaction path is suggested for obtaining from I the unknown isomeric structure V, 3-oxo-1H-1,2,3-triazolo[3,4-a]pyridine. Compound II is predicted as an unstable orange-red substance which should be handled and kept at low temperatures.     

Heterocyclization of cycloalkenes with di(2-pyridyl) diselenide in the presence of antimony pentachloride

Cycloalkenes react with di(2-pyridyl) diselenide in the presence of antimony pentachloride with the formation of products of the selenenylating electrophile cycloaddition at the multiple bond. The final products of heterocyclization, chloroantimonates(III) of 2,3-dihydro[1,3]selenazolo[3,2-a]pyridinium derivatives were isolated.     

Synthesis of 2,3-dihydroselenazolo[3,2-a]pyridinium salts based on reactions of pyridine-2-selanyl chloride with alkenes and dienes

The reaction of pyridine-2-selanyl chloride with alkenes and dienes gives 2,3-dihydro[1,3]selenazolo- [3,2-a]pyridinium derivatives as addition-cyclization products involving closure of the ring at the pyridine nitrogen atom of the selanylating electrophile.     

Studies with Polyfunctionally Substituted Heterocycles: New Synthesis of Pyrido[5′, 4′:2,3][1,3,4]oxadiazolo[3,2-a]pyridine; Pyridazine; 1,3,4-Oxadiazote; and Pyrazolo[1,5-a]Pyrimidine Derivatives

Cyanoacetohydrazide 1a reacts with 2-arylhydrazoketons 2a,b and 3a,b in refluxing ethanol to yield pyrido[5′,4′:2,3][1,3,4]oxadiazolo[3,2-a]pyridine and pyridazine derivatives; in the absence of solvent pyrazolo[1,5-a]pyrimidine derivatives were obtained. The reaction of 2a,b and 3a,b will) benzoylhydrazine afforded 1,3,4-oxadiazole and pyrazole derivatives.     

Condensed isoquinolines 31. Reaction of 5-aryl-3-halo-12H-isoquino[2,3-a]quinazolines with electrophilic reagents

Treatment of 5-aryl-3-halo-12H-isoquino[2,3-a]quinazolines with electrophilic reagents readily forms their oxidation products. Acylation of the 3-chloro-5-phenyl-7,12-dihydroisoquino[2,3-a]quinazolinium perchlorate with Ac₂O in the presence of pyridine gave the product of electrophilic substitution at the C-7 atom 1-(3-chloro-5-phenyl-12H-isoquino[2,3-a]quinazolin-7-yl)-1-ethanone. By the same route phenacyl bromides react with the anhydro base 1 to give 5-aryl-7-(2-aryl-2-oxoethyl)-3-halo-isoquino[2,3-a]quinazolin-13-ium bromides. These salts readily react with nucleophilic reagents to form the products of addition at the C-12 atom. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 1044–1052, July, 2008.     

A versatile synthesis of benzothieno-annelated 1,2-dihydropyridine and 1,2,3,4-tetrahydropyridine derivatives: the effect of the structure of benzothieno-annelated pyridinium salts on their reduction by sodium borohydride

Abstract  

Benzothieno[2,3-c]pyridinium and benzothieno[2,3-c]quinolinium salts were synthesized either by quaternization of benzothieno[2,3-c]pyridines, or recyclization of benzothieno[2,3-c]pyrylium salts with primary amines. One-pot synthesis of benzothieno[3,2-g]indolizinium salts from 1-(3-chloropropyl)-benzothieno[2,3-c]pyrylium included consequent recyclization of the pyrylium core by ammonia into a pyridine intermediate and its further intramolecular quaternization reaction. Depending on the structure of benzothieno-annelated pyridinium salts, their reaction with sodium borohydride in methanol results in reduction of the pyridine core into tetrahydropyridine or dihydropyridine derivatives. Whereas reduction of benzothieno[2,3-c]pyridinium and benzothieno[3,2-g]indolizinium salts readily yields benzothieno-annelated tetrahydropyridines as a complex mixture of stereoisomers, reduction of benzothieno[2,3-c]quinolinium salts results in dihydropyridine derivatives. The structure of the latter, in particular, was confirmed by single-crystal X-ray diffraction analysis.     

Syntheses of bisheterocycles from 2-hydrazino-3-aminopyridine

2-Hydrazino-3-aminopyridine reacts with carbon disulfide in an alkaline medium to give 1H-3-aminoimidazo[4,5-b]pyridine-2-thione and in a neutral medium to give 8-amino-3-thio-sym-triazolino[4,3-a]pyridine. The reaction of 2--methylhydrazino-3-aminopyridine with carbon disulfide leads to anhydro-1-methyl-3-mercapto-8-amino-sym-triazolo[4,3-a]pyridinium betaine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 411–413, March, 1977.     

Preparation of new nitrogen-bridged heterocycles 72. A new approach to 1-acyl-3-(substituted methylthio)thieno[3',4':4,5]imidazo[1,2-a]pyridine derivatives. [corrected

The alkaline treatment of the pyridinium salts, readily available from the S-alkylations of 3-amino-4-(1-pyridinio)thiophene-5-thiolates with various alkyl halides, in chloroform at room temperature afforded the corresponding thieno[3',4':4,5]imidazo[1,2-a]pyridine derivatives in low to moderate yields via the intramolecular cyclization of the resulting 1,5-dipoles followed by the aromatization of the primary cycloadducts. Interestingly, the reactions using unsymmetrical 3-amino-4-[1-(3-methylpyridinio)]thiophene-5-thiolates afforded only 8-methylthieno[3',4':4,5]imidazo[1,2-a]pyridines and the other 6-methyl derivatives were not formed at all. In addition the isolation of a byproduct in the condensation reaction of pyridinium salt with the solvent (CHCl?) is also discussed.     

Synthesis and molecular structure of 3-(2-aryl-2-oxoethyl)-3-methoxy-2-oxo-2,3-dihydroimidazo-[1,2-<Emphasis Type="Italic">a</Emphasis>]pyridine hydrochlorides

Reactions between 2-pyridylamides of Z-4-aryl-2-hydroxy-4-oxobut-2-enoic acids with diazomethane have been used to synthesize 3-(2-aryl-2-oxoethyl)-3-methoxy-2-oxo-2,3-dihydroimidazo[1,2-a]pyridines, which form hydrochlorides with hydrochloric acid. The structure of the latter has been demonstrated by XRD for the hydrochloride of 3-methoxy-2-oxo-3-(2-phenyl-2-oxoethyl)-2,3-dihydroimidazo[1,2-a]pyridine. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 464–468, 2007.     

Rearrangement of aryl- and benzylthiopyridinium imides with participation of a methyl substituent

6-Methyl substituted 2-aryl- and 2-benzylthiopyridinium N-imides reacted with an excess of isocyanates to give N,N-disubstituted exocyclic1H-imidazo[4,5-b]pyridin-2(3H)-ones. The products easily underwent spontaneous [1,5] hydrogen shift to provide the heteroaromatic imidazopyridinone isomers. The transformation implied the initial formation of [1,2,4]triazolo[2,3-a]pyridinium salt, followed by deprotonation and carbamoylation of the methylene moiety, and, finally, a rearrangement following a [1,3] sigmatropic pattern. Mechanistic considerations suggest and some experimental findings reveal the nonconcerted two-step mechanism of the ring transformation step.     

Nitroazines. 12 Reaction of 6-nitroazolo[1,5-a]pyrimidines with acetonitriles

Reaction of 6-nitroazolo[1,5-a]pyrimidines with cyanoacetamide, cyanoacetthioamide, or benzoylacetonitrile results in the conversion of the pyrimidine ring into a pyridine ring with the formation of 2-azolylamino-5-nitropyridines. Treatment of the latter with alcoholic sodium carbonate, or reaction of the azolopyrimidines with acetonitriles in an alkaline medium, affords 7-nitroazolo]1,5-a]pyrido[2,3-d]pyrimidines.See [1] for communication 11.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 256–291, February, 1991.     

Ultraviolet absorption spectra of pyridinium N-oxide perchlorates in acetonitrile

The UV Spectra of pyridinium N-oxide perchlorates were determined in acetonitrile and compared with the spectrum of pyridine N-oxide. The spectrum of pyridine N-oxide perchlorate is entirely different from the spectra of hydride-bis-pyridine N-oxide perchlorate and pyridine N-oxide. The spectrum of hydride-bis-pyridine N-oxide perchlorate/basic salt/ is similar to that of the conjugate base, but it is not a linear combination of the spectra of the protonated and the unprotanated base species.     

Reaction of diketene with cyanothioacetamide: A convenient and regioselective method for the preparation of new 4(1H)-pyridone derivatives

The reaction of diketene with cyanothioacetamide in dry dioxane in the presence of triethylamine gives triethylammonium 3-cyano-6-methyl-4-oxo-1,4-dihydro-2-pyridinethiolate. The regioselective S-alkylation of this thiolate is a convenient method for the preparation of substituted 4(1H)-pyridones and also derivatives of thiazolo[3,2-a]pyridine and thieno[2,3-b]pyridine. The action of 2-amino-1,1,3-tricyanopropene on this thiolate leads to its transformation into a new heterocyclic system, namely, 5H-pyrido[2′,3′:4,5]thiopyrano[2,3-b]pyridine; treatment with iodine yields the oxidation product, namely, the corresponding bis(2-pyridyl) disulfide. The structure of isopropyl (3-cyano-6-methyl-4-oxo-1,4-dihydro-2-pyridinyl)thioacetate was confirmed by X-ray diffraction structural analysis. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 716–725, May, 2007.     

4,4-Dialkyl-substituted N-Methylmorpholinium 3,5-Dicyano-6-oxo-1,4,5,6-tetrahydropyridine-2-thiolates and Some of Their Properties

4,4-Dialkyl-substituted N-methylmorpholinium 3,5-dicyano-6-oxo-1,4,5,6-tetrahydropyridine-2-thiolates were synthesized by the condensation of 2-alkyl-2-cyanoethyl crotonates with cyanothioacetamide and N-methylmorpholine. They were used for the production of substituted 2-alkylthio-1,4,5,6-tetrahydropyridines, 2-acetylthio-1,4,5,6,-tetrahydropyridine, 6-hydrazino-1,4,5,6-tetrahydropyridine, and 2,3,4,5,6,7-hexahydrothiazolo[3,2-a]pyridine. The structure of 6-bromo-3-bromomethyl-6,8-dicyano-7,7-dimethyl-2,3,4,5,6,7-hexahydrothiazolo[3,2-a]pyridine was proved by X-ray crystallographic analysis.