Halocyclization of 3-allylthio-5H-[1,2,4]triazino[5,6-<Emphasis Type="Italic">b</Emphasis>]indole

The synthesis of 3-allylthio-5H-[1,2,4]triazino[5,6-b]indole has been carried out by the reaction of 3-mercapto-5H-[1,2,4]triazino[5,6-b]indole with allyl bromide in the NaOH–H₂O–DMSO system and in a one-pot synthesis from isatin-β-thiosemicarbazide. Halocyclization of allylthio-5H-[1,2,4]-triazino[5,6-b]indole synthesized the 3-halomethyl-3,10-dihydro-2H-[1,3]thiazolo[3',2':2,3][1,2,4]-triazino[5,6-b]indolium halides.     

Halocyclization of 3-{[2-methyl(bromo)prop-2-en-1-yl]-sulfanyl}-5<Emphasis Type="Italic">H</Emphasis>-[1,2,4]triazino[5,6-<Emphasis Type="Italic">b</Emphasis>]indoles

Reactions of 3-[(2-bromoprop-2-en-1-yl)sulfanyl]-5H-[1,2,4]triazino[5,6-b]indole with bromine and of 3-[(2-methylprop-2-en-1-yl)sulfanyl]-5H-[1,2,4]triazino[5,6-b]indole with iodine and bromine afforded 3-halomethyl-10H-[1,3]thiazolo[3′,2′: 2,3][1,2,4]triazino[5,6-b]indol-4-ium halides whose structures were determined by ¹H NMR and X-ray analysis.     

Synthesis and antimicrobial activity of novel fused [1,2,4]triazino[5,6-<Emphasis Type="Italic">b</Emphasis>]indole derivatives

Synthesis of new fused systems of triazino[5,6-b]indole starting with preparation of 3-amino[1,2,4]-triazino[5,6-b]indole 1 by reaction of isatin with 2-aminoguanidinium carbonate in boiling acetic acid is presented [1]. Intermediate compound 1 reacted with aldehyde, ethyl chloroformate, triethyl orthoformate, and ninhydrine and gave new heterotetracyclic nitrogen systems, such as 3-(N ²-guanidinylimino)indole-2(1H)-one 2, 3-(N-ethoxycarbonylamino)-4H-[1,2,4]triazino[5,6-b]indole 3, 3-(N-ethoxymethyleneamino)-4H-[1,2,4]-triazino[5,6-b]indole 4, 3-(hydrazinothiocarbonylamino)-4H-[1,2,4]triazino[5,6-b]indole 5, respectively. N-(1,3-dioxoindene-2-ylidene)-4H-[1,2,4]triazino[5,6-b]indol-3-amine 6 was synthesized by reaction of compound 1 with aldehyde, ethyl chloroformate, triethyl orthoformate, and ninhydrine. New fused indole systems, pyrimido[2′,1′:3,4][1,2,4]triazino[5,6-b]indol-3(4H)-one 8, 9, 11, 12 and 1H-imidazo[2′,1′:3,4][1,2,4]triazino-[5,6-b]indol-2(3H)-one 10, were synthesized in the reaction of the intermediate 1 with bifunctional compounds. Structures of the products were elucidated from their elemental analysis and spectral data (IR, ¹H and ¹³C NMR and mass spectra). Antimicrobial activity of some synthesized compounds was tested.     

Ultrasound-Assisted Synthesis of 5<Emphasis Type="Italic">H</Emphasis>-Chromeno[2,3-<Emphasis Type="Italic">b</Emphasis>]pyridine Derivatives

An environmentally friendly method has been developed for the preparation of 5H-chromeno[2,3-b]pyridine derivatives in an aqueous medium under ultrasound irradiation.     

Synthesis of N-Substituted Methyl 4<Emphasis Type="Italic">H</Emphasis>-Thieno[3,2-<Emphasis Type="Italic">b</Emphasis>]pyrrole-5-carboxylates

The alkylation of methyl 4H-thieno[3,2-b]pyrrole-5-carboxylate with methyl iodide and allyl, propargyl, and benzyl bromides in the presence of sodium hydride in THF afforded the corresponding N-substituted derivatives. Some reactions of the alkylation products were studied.     

Organocatalytic approach toward the green one-pot synthesis of novel benzo[<Emphasis Type="Italic">f</Emphasis>]chromenes and 12<Emphasis Type="Italic">H</Emphasis>-benzo[5,6]chromeno[2,3-<Emphasis Type="Italic">b</Emphasis>]pyridines

An efficient tandem reaction approach is described to prepare novel benzo[f]chromenes from 2,3-dihydroxynaphthalene, malononitrile and aldehydes using 10 mol% guanidine hydrochloride as the catalyst under solvent-free conditions. The method was also extended to the preparation of novel 12H-benzo[5,6]chromeno[2,3-b]pyridines from 2-aminoprop-1-ene-1,1,3-tricarbonitrile instead of malononitrile under the same reaction conditions. The described one-pot three-component reaction is characterized by short reaction times, high-product yield, mild reaction conditions, simple workup procedure, and simple purification.     

Alkylation of 3-methyl-1<Emphasis Type="Italic">H</Emphasis>-acenaphtho[5,6-<Emphasis Type="Italic">de</Emphasis>]pyridazine

Alkylation of 3-methyl-1Н-acenaphtho[5,6]pyridazine with methyl and propyl iodides as well as with benzyl chloride in alkaline medium leads to the formation of the corresponding both N- and С-substituted pyridazine derivatives and also to the dimerization product of the initial compound. The ratio of obtained compounds depends on the used hydride, reaction temperature, and solvent.     

New syntheses of cycloalka[<Emphasis Type="Italic">b</Emphasis>]indoles

The review summarizes most recent synthetic approaches to compounds containing a cycloalka[b]- indole fragment as the main structural unit. Improved procedures for the preparation of cycloalka[b]indole heterocycles have been described, and their applications in the synthesis of natural and synthetic biologically active congeners have been considered.     

Synthesis and properties of a new fused heterocyclic system 12<Emphasis Type="Italic">H</Emphasis>-benzo[5,6][1,2,4]triazepino[3,4-<Emphasis Type="Italic">a</Emphasis>]isoindol-5(6<Emphasis Type="Italic">H</Emphasis>)-one

12H-Benzo[5,6][1,2,4]triazepino[3,4-a]isoindol-5(6H)-one was synthesized by the condensation of anthranilic acid hydrazide with o-phthalaldehyde. The structure of this compound was established by the X-ray diffraction study of its isopropyl derivative. The mechanism of formation of this compound was suggested and its alkylation reactions were investigated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 180–185, January, 2008.     

Nitration of 1,3-dihydro-2<Emphasis Type="Italic">H</Emphasis>-imidazo[4,5-<Emphasis Type="Italic">b</Emphasis>]pyridin-2-one derivatives

Nitration of 1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-one and its N-methyl derivatives at 0–5°C and 60°C gives 5-nitro-and 5,6-dinitro-1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-ones, respectively. The latter can also be obtained by nitration of 5-mononitro derivatives under similar conditions. The nitration of 6-chloro-and 6-bromo-1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-ones and their N-methyl-substituted analogs leads to the formation of the corresponding 6-chloro(bromo)-5-nitro compounds. The same products are formed in the nitration of 5,6-dichloro-and 5,6-dibromo-1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-ones. In this case, the process involves replacement of the halogen atom in position 5 of the pyridine fragment by nitro group. The nitration of 6-bromo-5-methyl-1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-one is accompanied by oxidation of the 5-methyl group to carboxy.     

Synthesis and antimicrobial activity of 2<Emphasis Type="Italic">H</Emphasis>-pyrimido[2,1-<Emphasis Type="Italic">b</Emphasis>]benzothiazol-2-ones

4-Phenyl-2H-pyrimido[2,1-b]benzothiazol-2-ones have been synthesized in quantitative yields by the reaction of 2-aminobenzothiazoles with alkynoic acid. The antimicrobial activity of the synthesized compounds was tested against bacterial species, Bacillus coagulans, Bacillus subtilis, Staphylococcus aureus, and Pseudomonas aeruginosa. The synthesized compounds have shown significant activity against microorganisms which can be correlated with the fused heterocyclic systems.     

Electrophilic cyclization of <Emphasis Type="Italic">N</Emphasis>-allyl(propargyl)-5-amino-1<Emphasis Type="Italic">H</Emphasis>-pyrazole-4-carboxamides. Synthesis of 4-[(dihydro)oxazol-2-yl]-1<Emphasis Type="Italic">H</Emphasis>-pyrazol-5-amines

N-Allyl-5-amino-1H-pyrazole-4-carboxamides in reactions with polyphosphoric acid, with N-halosuccinimides in chloroform, and with (chlorosulfanyl)benzenes in nitromethane in the presence of lithium perchlorate underwent cyclization involving the N-allylamide fragment to give 4-[5-methyl(halomethyl)-4,5-dihydrooxazol-2-yl]-1H-pyrazol-5-amines and 2-(5-amino-1H-pyrazol-4-yl)-5-[(arylsulfanyl)methyl]-4,5-dihydro-1,3-oxazolium perchlorates, respectively. Analogous reactions of N-propargyl-5-amino-1H-pyrazole-4-carboxamides with polyphosphoric acid afforded 4-(5-methyloxazol-2-yl)-1H-pyrazol-5-amines, and with (chlorosulfanyl) benzenes, 2-(5-amino-1H-pyrazol-4-yl)-5-[(arylsulfanyl)methylidene]-4,5-dihydro-1,3-oxazolium perchlorates.     

Recyclization of 1,3-dialkyl-6-nitro-1<Emphasis Type="Italic">H</Emphasis>-imidazo[4,5-<Emphasis Type="Italic">b</Emphasis>]pyridine-2,5(3<Emphasis Type="Italic">H</Emphasis>,4<Emphasis Type="Italic">H</Emphasis>)-diones into imidazole derivatives

Treatment of 5-amino-1,3-dialkyl-2,3-dihydro-1H-imidazo[4,5-b]pyridin-2-ones with sodium nitrite in aqueous HCl gave 1,3-dialkyl-1H-imidazo[4,5-b]pyridine-2,5(3H,4H)-diones which were nitrated with potassium nitrate in sulfuric acid to 6-nitro derivatives, and the latter underwent recyclization into 4-amino-1,3-dialkyl-5-(1H-pyrazol-5-yl)-2,3-dihydro-1H-imidazol-2-ones by the action of hydrazine hydrate.     

Reactions of 3-Aroylpyrrolo[1,2-<Emphasis Type="Italic">a</Emphasis>]quinoxaline-1,2,4(5<Emphasis Type="Italic">H</Emphasis>)-triones with 2,3-Dihydrofuran and 3,4-Dihydro-2<Emphasis Type="Italic">H</Emphasis>-pyran

3-Aroylpyrrolo[1,2-a]quinoxaline-1,2,4(5H)-triones reacted with 2,3-dihydrofuran and 3,4-dihydro-2H-pyran to give mixtures of the corresponding hetero-Diels–Alder (furo- and pyrano[3″,2″: 5′,6′]pyrano- [4′,3′: 2,3]pyrrolo[1,2-a]quinoxalines) and Michael adducts (furyl- and pyranylpyrrolo[1,2-a]quinoxalines).     

New Synthesis of Pyrano[4,3-<Emphasis Type="Italic">d</Emphasis>]pyrazolo[3,4-<Emphasis Type="Italic">b</Emphasis>]pyridines

A new efficient method has been developed for the synthesis of highly biologically active pyrano-[4,3-d]pyrazolo[3,4-b]pyridines on the basis of Smiles rearrangement of ethyl [(8-alkyl(aryl)-5-cyano-3,3-dimethyl-3,4-dihydro-1H-pyrano[3,4-c]pyridin-6-yl)oxy]acetates. Intermediate acetohydrazides have also been isolated. The proposed procedure is advantageous due to the possibility of avoiding experimentally difficult chlorination stage.     

Synthesis and X-ray study of 6<Emphasis Type="Italic">H</Emphasis>-chromeno[3,4-<Emphasis Type="Italic">e</Emphasis>][1,3,4]triazolo[2,3-<Emphasis Type="Italic">a</Emphasis>]pyrimidine

2-Dimethylamino methylenechromanone 1 reacted with 4H-1,2,4-triazol-3-amine in acetic acid to give only one isolated product which was identified by X-ray study as 6H-chromeno[3,4-e][1,3,4]triazolo[2,3-a]-pyrimidine. The molecular structure of 3, C₁₂H₈N₄O, was determined to be monoclinic, P2₁/c, a = 16.3875(5), b = 8.8378(3), c = 13.8392(5) Å, β = 101.190(1)°, V = 1966.22(11) ų, Z = 8.     

Fluorinated [1,2,4]triazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidines and [1,2,4]triazolo[5,1-<Emphasis Type="Italic">c</Emphasis>][1,2,4]triazines*

The reaction of 3-R-5-amino-1,2,4-triazoles with the ethyl ester of 2-fluoroacetoacetic acid gave 2-R-fluoro[1,2,4]triazolo[1,5-a]pyrimidin-7(4H)-ones. The reaction of a 3-R-1,2,4-triazolyl-5-diazonium salt with the ethyl ester of 2-fluoroacetoacetic acid and subsequent cyclization of the triazolylhydrazones lead to 7-R-3-fluoro[1,2,4]triazolo[5,1-c][1,2,4]triazin-4(1H)-ones.     

Synthesis and biological evaluation of novel active arylidene derivatives of 5,6-dihydro-4<Emphasis Type="Italic">H</Emphasis>-cyclopenta[<Emphasis Type="Italic">b</Emphasis>]- and 4,5,6,7-tetrahydrobenzo[<Emphasis Type="Italic">b</Emphasis>]-thiophene-2-carboxylic acid

A series of novel arylidene derivatives of 5,6-dihydro-4H-cyclopenta[b]-thiophene-2-carboxylic acid and 4,5,6,7-tetrahydrobenzo[b]-thiophene-2-carboxylic acid were synthesized by reacting benzylidene derivatives of chloro aldehyde with 2-mercaptoacetic acid. Benzylidene derivatives of chloro aldehyde were prepared from Vilsmeier reaction of 2-benzylidenecyclopentanone and 2-benzylidenecyclohexanone derivatives, obtained from condensation of various aromatic aldehydes with cyclopentanone and cyclohexanone. All synthesized compounds were characterized by nuclear magnetic resonance (NMR), infrared (IR), and mass spectroscopy and X-ray single-crystal analysis. The synthesized compounds were screened for their in vitro antimicrobial and antifungal activity. Good antimicrobial activity, especially against methicillin-resistant Staphylococcus aureus, was observed for most of the compounds tested. In particular, compound 9f emerged as an effective antibacterial agent and may be a potential candidate for future drug discovery and development.     

Azines and azoles: CXXVII. 5-phenyl-7<Emphasis Type="Italic">H</Emphasis>-[1,2,4]triazolo[5,1-<Emphasis Type="Italic">b</Emphasis>][1,3]thiazin-7-ones: Synthesis and structure

Reactions of 1-acylthiosemicarbazides with methyl 3-phenylprop-2-ynoate provide a new one-step procedure for the synthesis of 2-substituted 5-phenyl-7H-[1,2,4]triazolo[5,1-b][1,3]thiazin-7-ones. The product structure was determined on the basis of scalar spin-spin coupling constants ² J(¹H-¹⁵N) and ³ J(¹H-¹⁵N) in the ¹H and ¹⁵N NMR spectra and was proved by X-ray analysis. Methyl 3-phenylprop-2-ynoate reacted with 1-acetylthiosemicarbazide in ethanol in the presence of H₂SO₄ to give 3-methyl-7-phenyl[1,2,4]triazolo[3,4-b]-[1,3]thiazin-5-one as the only product.