Nitration of Pyrrolo[1,2-<Emphasis Type="Italic">a</Emphasis>]pyrazines

We have synthesized nitro derivatives of pyrrolo[1,2-a]pyrazines using a nitrating mixture and acetyl nitrate. We have obtained the products of oxidation of the side chain of 1,6-substituted pyrrolo[1,2-a]-pyrazines. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1579–1586, October, 2005.     

Trifluoroacetylation of pyrrolo[1,2-<Emphasis Type="Italic">a</Emphasis>]pyrazines

A study was carried out on the reaction of pyrrolo[1,2-a]pyrazines containing an alkyl, aryl, or aralkyl substituent at C-1 with trifluoroacetic anhydride. Trifluoroacetylation products may be formed either by reaction in the pyrrole ring or at the aryl or aralkyl groups at C-1. Products of electrophilic substitution at C-6 are formed in the trifluoroacetylation of pyrrolo[1,2-a]pyrazines containing at C-1 a substituent bulkier than a methyl group but lacking substituents at C-6 (the α-position of the pyrrole ring). __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1226–1233, August, 2007.     

Formylation of pyrrolo-[1,2-<Emphasis Type="Italic">a</Emphasis>]pyrazines

The formylation of pyrrolo[1,2-a]pyrazines containing alkyl, aryl, or hetaryl substituents in positions 1 and 6 of the heterocycle has been studied. It has been shown that formylation of 1-phenyl-and 1-(2 thienyl)pyrrolo[1,2-a]pyrazine occurs selectively at the α-position of the pyrrole ring. In all of the remaining examples the reaction course depends on substituent, reagent ratio, and reaction time. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 88–93, January, 2008.     

Stereoselective synthesis of 4-substituted 1,2,3,4,10,10a-hexahydropyrazino[1,2-<Emphasis Type="Italic">a</Emphasis>]indoles

4-Substituted 1,2,3,4-tetrahydropyrazino[1,2-a]indoles were synthesized from 2-cyanoindole. (R)-4-Methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indole was obtained by the Mitsunobu reaction. Stereoselective reduction of 4-substituted 1,2,3,4-tetrahydropyrazino[1,2-a]indoles gave 4-substituted 1,2,3,4,10,10a-hexahydropyrazino[1,2-a]indoles. (4R, 10aR)-4-Methyl-1,2,3,4,10,10a-hexahydropyrazino[1,2-a]indole was synthesized.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 221–225, January, 2005.     

Fluorine-containing pyrido[1,2-<Emphasis Type="Italic">a</Emphasis>]quinazolin-6-ones

Reactions of 2-aminopyridine and 2-amino-5-methylpyridine with 2,3,4,5-tetrafluorobenzoyl chloride afforded N,N’-diaroylpyridinium salts, which were converted into 6H-pyrido[1,2-a]quinazolin-6-ones by refluxing in toluene in the presence of triethylamine. The angular structure of the tricyclic derivatives obtained was confirmed by ¹⁹F and ¹³C NMR spectroscopy and 2D heteronuclear HetCOR and HMBC experiments.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2216–2220, October, 2004.     

11H-isoindolo[2,1-<Emphasis Type="Italic">a</Emphasis>]benzimidazoles (Review)

Data on methods for the synthesis of isoindolo[2,1-a]benzimidazole and its derivatives and their chemical characteristics are reviewed. Data from quantum-chemical calculations of certain structures are presented. Possible practical applications of the compounds are indicated. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 323–351, March, 2007.     

Synthesis and properties of pyrimido[4,5-<Emphasis Type="Italic">a</Emphasis>]- and pyrido[4,3-<Emphasis Type="Italic">a</Emphasis>]carbazole derivatives

Methods for the synthesis of substituted pyrimido [4,5-a]- and pyrido[4,3-a]carbazoles were proposed. Condensation of 2-(dimethylaminomethylene)-6-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-one with guanidine and thiourea afforded 2-amino-8-methyl-6,11-dihydro-5H-pyrimido[4,5-a]carbazole and 8-methyl-3,5,6,11-tetrahydro-2H-pyrimido[4,5-a]carbazole-2-thione, respectively. The reaction of cyano(6-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-ylidene)acetamide with dimethylformamide dimethyl acetal gave N-(dimethylamino-methylene)cyano(6-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-ylidene)acetamide. Cyclization of the latter yielded 1-cyano-8-methyl-3,5,6,11-tetrahydro-2H-pyrido[4,3-a]carbazol-2-one.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2740–2744, December, 2004.     

Transformations of 8-substituted tetrazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrazines

The reactions of 8-chlorotetrazolo[1,5-a]pyrazine with N-, O-, and S-nucleophiles involve the ipso substitution of the chlorine atom. Heating of this compound with benzotriazole or phenyltetrazole results in elimination of the nitrogen molecule from one of the tetrazole rings to form new annelated azapentalenes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 334–338, February, 2007.     

One-Pot Three-Component Synthesis of 3-Aminoimidazo[1,2-<Emphasis Type="Italic">a</Emphasis>]pyridines and -pyrazines in the Presence of Silica Sulfuric Acid

Summary. The synthesis of 3-aminoimidazo[1,2-a]pyridines and 3-aminoimidazo[1,2-a]pyrazines through a condensation reaction of 2-aminopyridine or 2-aminopyrazine, aldehyde, and alkyl or aryl isocyanide in high yields at room temperature in the presence of silica sulfuric acid is described.     

The synthesis of aminoimidazo[1,2-<Emphasis Type="Italic">a</Emphasis>]azinecarboxylic acid esters from ethyl glyoxylate

Three-component reactions of aminoazines, isonitriles, and ethyl glyoxylate gave mixtures of isomeric ethyl 2-and 3-aminoimidazo[1,2-a]azinecarboxylates in moderate yields. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 539–541, March, 2007.     

2-(Adamantan-1-yl)imidazo[1,2-<Emphasis Type="Italic">a</Emphasis>]pyridines and Their Derivatives

A series of 1-adamantylimidazo[1,2-a]pyridines has been synthesized. The negative influence of electron-acceptor substituents in the pyridine ring on the alkylation of substituted 2-aminopyridines with bromomethyl (adamantan-1-yl) ketone has been demonstrated. Bromination of adamantylimidazo-[1,2-a]pyridines on boiling in liquid bromine or in the presence of a Lewis acid resulted in insertion of a bromine atom in the imidazole ring without affecting the adamantane nucleus. The compounds studied take part in the Ritter reaction despite the absence of an easily removed groups in the adamantane nucleus.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, 761–766, May, 2005.     

Synthesis of substituted pyrido[1,2-<Emphasis Type="Italic">a</Emphasis>]pyrimidines from 2-arylmethylidene-3-fluoroalkyl-3-oxopropionates

Cyclocondensation of 2-arylmethylidene-3-fluoroalkyl-oxopropionates with 2-amino-pyridine occurs at both the polyfluoroacylvinyl and alkoxycarbonylvinyl fragments to give alkyl 4-aryl-2-polyfluoroalkyl-4H-pyrido[1,2-a]pyrimidine-3-carboxylates and 4-aryl-2-hydroxy-3-polyfluoroacyl-4H-pyrido[1,2-a]pyrimidines, respectively. When treated with copper(II) acetate, the pyrido[1,2-a]pyrimidines yield metal complexes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2745–2749, December, 2005.     

Tandem transformations of tetrahydropyrrolo[3,2-<Emphasis Type="Italic">c</Emphasis>]pyridines under the action of dimethyl acetylenedicarboxylate. A novel route to pyrrolo[2,3-<Emphasis Type="Italic">d</Emphasis>]azocines

Reactions of substituted tetrahydropyrrolo[3,2-c]pyridines with dimethyl acetylenedicarboxylate in protic and aprotic solvents were studied. A novel single-step method for the synthesis of pyrrolo[2,3-d]azocine derivatives was developed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2513–2519, November, 2005.     

Xylogranatinin,a new pyrido[1, 2-<Emphasis Type="Italic">a</Emphasis>]pyrazine alkaloid from the fruit of a Chinese mangrove <Emphasis Type="Italic">Xylocarpus granatum</Emphasis>

9-Hydroxy-3-methoxy-6H-pyrido[1,2-a]pyrazin-6-one, a new pyrido[1,2-a]pyrazine alkaloid named xylogranatinin, was isolated from the fruit of a Chinese mangrove Xylocarpus granatum. Its structure was elucidated on the basis of spectroscopic data, especially 2D NMR techniques including HSQC and HMBC. To the best of our knowledge, this is the first time that a pyrido[1,2-a]pyrazine alkaloid was found as a natural product. Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 351–352, July–August, 2007.     

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.