Synthesis of pyrido[3,4-b]pyrano[3,4-b]indoles

The synthesis of some pyrido[3,4-b]pyrano[3,4-b]indoles ( 3 ) from 3-hydroxy-4-(3-indolyl)piperidines ( 6 ) is reported.     

Chemistry of furazano[3,4-b]pyrazine 6. 1,2,3-triazolo[4,5-b]furazano[3,4-b]pyrazines

The reduction of 1,2,3-triazolo[4,5-e]furazano[3,4-b]pyrazine 6-oxide was investigated. By means of data from x-ray crystallographic analysis it was shown that there is a relation between the aromaticity and the structure of the obtained triazoles.For communication 5, see [1].Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1259–1264, September, 1998.     

Synthesis of pyrazolo[3,4-b][1,4]diazepines and pyrazolo[3,4-b]pyrazines

The synthesis and structure elucidation of new pyrazolo[3,4-b][1,4]diazepines and pyrazolo[3,4-b]pyrazines are reported and the characterisation of isomers and tautomers by proton and carbon-13 nmr are discussed. In some case only NOE experiments allow us to identify the isomeric structure.     

Synthesis of enantiomerically pure perhydrofuro[3,4-b]pyrans and perhydrofuro[3,4-b]furans

Olefinic diols, prepared from (R)-(+)-2,2-dimethyl-1,3-dioxolane-4-carboxaldehyde via olefination and hydrolysis, were converted into enantiomerically pure hydroxy substituted tetrahydrofuran derivatives by cyclization using N-phenylselenophthalimide and BF₃. The PhSe group in the C-4 position of these tetrahydrofurans was then substituted by an allyl group using allyltributylstannane in the presence of AIBN. The selenium promoted cyclizations of the allyl tetrahydrofurans in which the OH and the allyl groups are trans to each other formed the enantiopure perhydrofuro[3,4-b]pyrans, while the cyclization of the allyl tetrahydrofurans in which the OH and the allyl groups are cis gave rise to the perhydrofuro[3,4-b]furans. These bicyclic products were finally deselenenylated with triphenyltin hydride and AIBN.     

Selenium heterocycles. XXXIII. Synthesis of thieno[3,4-b]furan,seleno[3,4-b]furan,thieno[3,4-b]indole and seleno[3,4-b]indole. four novel heterocycles

Starting from the readily available 2-methyl-3-benzoylfuran, 1-phenylthieno[3,4-b]furan and 1-phenyl-seleno[3,4-b]furan were prepared. Also, starting from phenyl 3-methylindol-2-yl ketone and aryl 2-methyl-indole-3-yl ketones a series of substituted thieno[3,4-b]indoles and substituted seleno[3,4-b]indoles were prepared.     

Dihydropyrrolo[3,4-b]- and dihydropyrimido[4,5-b]indoles

Aromatic aldehydes react with indole-2-carboxylic acid azides under acid catalysis conditions to give the corresponding 3-(-halobenzyl)indoles, which react with aliphatic and aromatic amines to give the corresponding aminobenzylindoles. The latter undergo intramolecular cyclization to dihydropyrrolo[3,4-b]indoles at room temperature and are converted to dihydropyrimido[4,5-b]indoles through the Curtius rearrangement when they are heated to 80-110°C. Acetylation of the latter products gives N- and O-acetyl derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 935–939, July, 1982.     

Synthesis of 1H-thieno[3,4-c]pyrazoles,thieno[3,4-b]furans,selenolo[3,4-b]furans and pyrrolo[3,4-d]thiazoles

Starting from the readily available aryl 2-methyl-5-phenyl-3-furyl ketones, 5-methyl-1H-1-phenylpyrazole-4-yl ketones and 4-methyl-2-phenyl-5-thiazolylcarboxaldehyde, a series of 2-phenyl-4-arylthieno[3,4-b]-furan, 2-phenyl-4-(p-methoxyphenyl)selenolo[3,4-b]furan, 4-aryl-1H-1-phenylthieno[3,4-c]pyrazole and 5-benzyl-2-phenylpyrrolo[3,4-d]thiazole were prepared in high yield.     

Synthesis and halogenation of propargyl pyrazolo-[3,4-d]pyrimidine thioether

The reaction of 4-imino-1-methyl-5-phenyl-6-propargylthio-1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidine with halogens leads to the formation of (Z)-8-halomethylene-4-imino-1-methyl-5-phenyl-4,5,7,8-tetrahydro-1H-pyrazolo[4,3-e][1,3]thiazolo[3,2-a]pyrimidinium trihalide. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 1085–1088, July, 2008.     

Benzo[3,4]cyclobuta[1,2-b]thiophene

Tye synthesis of thieno[3,2-c]cinnoline is described; vapour phase thermolysis of this compound gives benzo[3,4]cyclobuta[1,2-b]thiophene.     

1,2,5-Thiadiazolo[3,4-b]pyrazines

1,2,5-Thiadiazolo[3,4-b]pyrazine and its derivatives were prepared. Nucleophilic displacements of halogen atoms on the nucleus were reported.     

1H-pyrazolo[3,4-b]pyridines

The synthesis of a number of new 1H-pyrazolo[3,4-b]pyridine-5-carboxylic acid derivatives is described. Most of these compounds have either an alkoxy or a basic substituent in position 4.     

C-phosphorylated furazano-[3,4-b]piperazines

The reaction of phosphorylated α-chloroacetaldehydes with 3,4-diaminofurazane gives enamines, bisenamines, semiaminals, and O,N-acetals, whose cyclization leads to previously unreported phosphorylated furazano[3,4-b]piperazines. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1220–1229, August, 2006.     

Isomerization of pyridazino [4,5-b] indoles to pyrrolo [3,4-b] indoles

The dihydropyridazine ring undergoes contraction to a dihydropyrrole ring to give 1-phenyl-2-benzylideneaminodihydropyrrolo[3,4-b]indol-3-ones when 1-phenyldihydropyridazino[4,5-b]indol-4-ones are treated with aromatic aldehydes under acid catalysis conditions. The reaction mechanism consists in the formation of a (3-indolyl)phenylmethyl cation, which leads to opening of the pyridazine ring and subsequent development of a bond between the carbonium center and the amide nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1406–1408, October, 1976.     

Chemistry of furazano[3,4-b]pyrazine. 4. 5,6-Dichlorofurazano[3,4-b]pyrazine in cyclization reactions

A method was developed for the production of polycyclic compounds containing the furazano[3,4-b]pyrazine fragment by the reaction of difunctional nucleophiles with 5,6-dichlorofurazano[3,4-b]pyrazine. It was shown that the reaction is affected by the hydrogen chloride acceptor (triethylamine). For Communication 3, see [1]. Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11. pp. 1561–1564, November, 1997.     

Chemistry of furazano[3,4-b]pyrazines

A method was developed for the synthesis of 5,6-dichlorofurazano[3,4-b]pyrazine (a compound with easily removed leaving groups). The optimum conditions for their substitution by various nucleophiles were determined.For Communication 2, see [1].Latvian Institute of Organic Synthesis, Riga. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1402–1416, October, 1997.     

Synthesis of pyridazino[3,4-b]quinoxalines and pyrazolo[3,4-b]-quinoxaline by 1,3-dipolar cycloaddition reaction

The pyridazino[3,4-b]quinoxalines 6a,b and pyrazolo[3,4-b]quinoxaline hydrochloride 9 were synthesized by the 1,3-dipolar cycloaddition reaction of 6-chloro-2-(1-methylhydrazino)quinoxaline 4-oxide 5 with dimethyl or diethyl acetylenedicarboxylate and 2-chloroacrylonitrile, respectively. The reaction mechanisms were postulated for the formation of 6a,b and 9 .     

Reactivity of sym-triazolo[3,4-b ]benzothiazole

The reactivity of sym-triazolo[3,4-b]benzothiazole (I) has been studied. Compound I is stable under the conditions of acid hydrolysis; when it is heated with acetic anhydride in the presence of sodium acetate or with an aqueous solution of alkali, the triazole ring opens with the formation of 2-acetylamino- and 2-aminobenzothiazoles, respectively. Compound I has been brominated in position 3 and has been subjected to the Vilsmeier and Mannich reactions. The thiosemicarbazone and oxime of sym-triazolo[3,4-b]benzothiazole-3-carbaldehyde have been obtained, and the oxime has been converted into the corresponding nitrile. The thioamide, ester, and hydrazide of sym-triazolo[3,4-b]benzothiazole-3-carboxylic acid have also been obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 7, pp. 916–919, July, 1970.     

Synthesis of 3-aryl-6H-isoxazolo[3,4-d]pyrazolo[3,4-b]pyridines and 3-aryl-6H-isoxazolo[5,4-d]pyrazolo[3,4-b]pyridines

The synthesis and characterization of a number of 3-aryl-6H-isoxazolo[3,4-d]pyrazolo[3,4-b]pyridines and 3-aryl-6H-isoxazolo[5,4-d]pyrazolo[3,4–6]pyridines from common precursors, 5-benzoyl-4-chloro-1H-pyrazolo-[3,4-b]pyridines, has been described. The structures were determined by unambiguous chemical synthesis and by isolation and ¹³C nmr analysis of some key, isolated, intermediates. The ability of these compounds to displace [3H]flunitrazepam from CNS binding sites was also observed.