A mild synthesis of [1,2,4]triazolo[4,3-a]pyridines

The reaction between 2-hydrazinopyridines and ethyl imidates was examined as a one-pot method for rapidly preparing [1,2,4]triazolo[4,3-a]pyridines. A diverse set of 2-hydrazinopyridines were cyclized with a variety of alkyl- and aryl-substituted ethyl imidates in good yields. The reaction proceeds optimally under mild conditions (50−70 °C) using 1.5 equiv of acetic acid. The electronic and steric properties of the hydrazine and imidate strongly impact the rate of the reaction. When highly electron deficient 2-hydrazinopyridines were used, the products rearranged to [1,2,4]triazolo[1,5-a]pyridines.     

A convenient synthesis of 2-aryl substituted benzo[f] [1,2,4]triazolo[1,5-a]azepine derivatives

A convenient synthetic pathway to 2-aryl-5,6-dihydro-4H-benzo[f][1,2,4]triazolo[1,5-α]azepine derivatives 7 was developed. The synthesis was based on the cycloaddition of the 1,2,3,4-tetrahydronaphthalene a-acetoxy azo compounds 3 with Ar-CN in the presence of AlCl3 and the consecutive ring enlargement.     

New syntheses of [1,2,5]oxadiazolo[3,4-e][1,2,3,4]tetrazine 4,6-dioxide

New methods were developed for the synthesis of [1,2,5]oxadiazolo[3,4-e][1,2,3,4]tetrazine 4,6-dioxide from 4-(tert-butyl-NNO-azoxy)-N-nitro-1,2,5-oxadiazol-3-amine or its alkali metal salts and acid anhydrides (or chlorides) in the presence of strong acids. The yield of [1,2,5]oxadiazolo[3,4-e][1,2,3,4]tetrazine 4,6-dioxide in acetic anhydride in the presence of sulfuric acid or sulfuric anhydride at 20°C in 20 min attained 83%. A general mechanism was proposed for the reactions under study. Acetyl group behaved for the first time as departing group in the synthesis 1,2,3,4-tetrazine 1,3-dioxides, and [1,2,5]oxadiazolo[3,4-e][1,2,3,4]tetrazine 4,6-dioxide was obtained in 47% yield from N-[4-(acetyl-NNO-azoxy)-1,2,5-oxadiazol-3-yl]acetamide.     

Push–Pull Derivatives Based on 2,4′-Biphenylene Linker with Quinoxaline, [1,2,5]Oxadiazolo[3,4-B]Pyrazine and [1,2,5]Thiadiazolo[3,4-B]Pyrazine Electron Withdrawing Parts

A series of novel V-shaped quinoxaline, [1,2,5]oxadiazolo[3,4-b]pyrazine and [1,2,5]thiadiazolo[3,4-b]pyrazine push–pull derivatives with 2,4′-biphenylene linker were designed and their electrochemical, photophysical and nonlinear optical properties were investigated. [1,2,5]Oxadiazolo[3,4-b]pyrazine is the stronger electron-withdrawing fragment as shown by electrochemical, and photophysical data. All compounds are emissive in a solid-state (from the cyan to red region of the spectrum) and quinoxaline derivatives are emissions in DCM solution. It has been found that quinoxaline derivatives demonstrate important solvatochromism and extra-large Stokes shifts, characteristic of twisted intramolecular charge transfer excited state as well as aggregation induced emission. The experimental conclusions have been justified by theoretical (TD-)DFT calculations.     

Synthesis of substituted [1,3]thiazolo[4,5-b]pyridines and [1,3]thiazolo[4,5-d][1,2,3]triazines

In this work, we described an easy preparation of substituted 4-amino-5-cyano-1,3-thiazoles. These compounds have been used as starting materials to obtain two classes of compounds. New substituted [1,3]thiazolo[4,5-e]pyridines were synthesized in one step via Friedländer reaction. Diazotation of 4-amino-5-cyano-1,3-thiazoles afforded 4-chloro[1,3]thiazolo[4,5-d][1,2,3]triazines in one step. The later was substituted by a secondary amine to obtain substituted 4-amino[1,3]thiazolo[4,5-d][1,2,3]triazines.     

New D–A–D luminophores of the [1,2,5]thiadiazolo[3,4-d]pyridazine series

Three [1,2,5]thiadiazolo[3,4-d]pyridazines containing 4,7-positioned indole-type substituents were synthesized from the corresponding 4,7-dibromo precursor employing the SNAr aromatic nucleophilic substitution. Photophysical properties and DFT calculations showed that the D–A–D dyes based on [1,2,5]thiadiazolo[3,4-d]pyridazine core exhibited fluorescence in the near infrared region of the spectrum, which makes them promising for use as an active emitting layer in NIR-OLEDs as well as for other possible applications as an IR luminophore.     

Synthesis of [1,2,4]triazolo[4,3-b]-s-tetrazines with incorporated furazan ring

Furazancarboxylic hydrazides can serve as nucleophiles to substitute for one dimethylpyrazole fragment in bis(3,5-dimethylpyrazol-1-yl)-s-tetrazine, giving the corresponding N??-[6-(3,5-dimethylpyrazol-1-yl)-s-tetrazin-3-yl]-4-R-furazan-3-carbohydrazides in good yields. Dehydration of the indicated carbohydrazides in polyphosphoric acid for the first time gave rise to [1,2,4]triazolo[4,3-b]-s-tetrazines containing the furazan ring as a substituent at the triazole ring.     

Synthesis and Diels-Alder reactions of the benzo[4,5]thieno [2,3-c]pyrrole ring system

The first synthesis of the parent compound of the benzo[4,5]thieno[2,3-c]pyrrole ring system and its derivatives, as well as their Diels-Alder reactions with DMAD and N-phenylmaleimide are reported. A new synthesis of the benzo[4,5]thieno[2,3-d]pyridazine ring system is also described.     

Efficient synthesis of 5,6-dihydro-8H-[1,2,4]thiadiazino[6,5,4-de]phenanthridine 4,4-dioxide and 5,6-dihydro-8H-[1,2,4]-thiadiazino[6,5,4-ij]thieno[2,3-c]quinoline 4,4-dioxide

A new efficient and versatile synthesis to obtain different substituted 5,6-dihydro-8H-[1,2,4]thiadiazino[6,5,4-de]phenanthridine 4,4-dioxide and 5,6-dihydro-8H-[1,2,4]-thiadiazino[6,5,4-ij]thieno[2,3-c]quinolone 4,4-dioxide was developed. The four cyclic systems are achieved by a three-step synthesis proceeding under mild conditions in high yields.     

Stereoselective alkylation of thiacalix[4]arenes

A direct tetraalkylation of thiacalix[4]arenes using procedures well established in ‘classical’ calixarene chemistry usually gives the 1,3-alternate conformers as the main product (n-PrI/K₂CO₃/acetone) while the cone conformers are obtained only in very poor yields (n-PrI/NaH/DMF). Surprisingly, the so far almost inaccessible cone conformers can be prepared in high yields using the two-step procedure: dialkylation-dialkylation, opening the way for their further utilisation in supramolecular chemistry.     

Preparation and Evaluation of 1,3-alternate 25,27-Bis-[p-nitrobenzyloxy]-26,28-bis-[3-propyloxy]-calix[4]arene-bonded Silica Gel Stationary Phase for LC

A novel 1,3-alternate 25,27-bis-[p-nitrobenzyloxy]-26,28-bis-[3-propyloxy]-calix[4]arene-bonded silica gel stationary phase has been prepared and used for separating various selected analytes by HPLC. The effect of organic modifier and pH of the mobile phase on retention and selectivity were studied using aromatic positional isomers as an example. Application examples have been provided for separation of alkylbenzenes, PAHs, xanthine derivatives, and purine and pyrimidine bases. A selectivity comparison of the novel phase versus CalixBz and Backerbond PhenylEthyl phases has been performed.     

Solid-phase synthesis of [1,2,4]triazolo[3,4-a]phthalazine and tetrazolo[5,1-a]phthalazine derivatives

A general method is reported for the solid-phase synthesis of [1,2,4]triazolo[3,4-a]phthalazine and tetrazolo[5,1-a]phthalazine derivatives based on the cyclization of resin-bound chlorophthalazines 4 with various hydrazides or sodium azide. The resin-bound chlorophthalazines 4, produced by nucleophilic aromatic substitution reaction of dichlorophthalazine with the secondary amine resins 2, served as the key intermediate for subsequent triazolophthalazine resins 6 and tetrazolophthalazine resins 8, which provided the desired products 7 and 9 in good yields and purities.     

Microwave assisted synthesis of 2,3-dihydro-4H-benzo[4,5]thiazolo[3,2-a]furo[2,3-d]pyrimidin-4-ones and 6,7-dihydro-5H-furo[2,3-d]thiazolo[3,2-a]pyrimidin-5-ones using Mn(OAc)3

2-Hydroxy-4H-benzo[4,5]thiazolo[3,2-a]pyrimidin-4-one 2a and 7-hydroxy-5H-thiazolo[3,2-a]pyrimidin-5-one 2b, were obtained in high yields under mild conditions from the cyclization reactions of bis-(2,4,6-trichlorophenyl) malonate and 2-aminobenzothiazole or 2-aminothiazole, respectively. A new class of compounds, 2,3-dihydro-4H-benzo[4,5]thiazolo[3,2-a]furo[2,3-d]pyrimidin-4-ones and 6,7-dihydro-5H-furo[2,3-d]thiazolo[3,2-a]pyrimidin-5-ones, were synthesized via the microwave assisted radical addition of compounds 2a and 2b to various alkenes using manganese(III) acetate. A preliminary acetylcholine esterase (AchE) inhibition test of compound 4e showed excellent (92%) inhibitory potential, comparable with the standard drug Donapezil®.     

Solvent-free combinatorial synthesis of tetrazolo[1,5-a]thiopyrano[3,4-d]pyrimidine derivatives

A series of novel tetrazolo[1,5-a]thiopyrano[3,4-d]pyrimidine derivatives were synthesized by reaction of aryl aldehyde, 2H-thiopyran-3,5(4H,6H)-dione, and 5-aminotetrazole under solvent-free conditions. The features of this procedure are mild reaction conditions, high yields, and operational simplicity.     

Cascade cyclization of aryldiynes using iodine: synthesis of iodo-substituted benzo[b]naphtho[2,1-d]thiophene derivatives for dye-sensitized solar cells

A facile, efficient, and general synthetic method for iodo-substituted benzo[b]naphtho[2,1-d]thiophenes has been developed via a cascade cyclization of thioanisole-substituted aryldiynes using iodine. A new donor–π linker–acceptor (D–π–A) organic dye, G1, with the benzo[b]naphtho[2,1-d]thiophene moiety as an electron donor has been synthesized, and the performance of dye-sensitized solar cell based on G1 has been investigated.     

One pot synthesis of imidazo[2,1-b]thiazoles and benzo[d]thiazolo[3,2-a]imidazoles

A series of imidazo[2,1-b]thiazole and benzo[d]thiazolo[3,2-a]imidazole analogues were synthesized by stirring an equimolar mixture of dibenzoylacetylene with imidazole/thiazole derivatives in toluene or acetonitrile at room temperature. The products were generated in good yields and characterized by standard analytical techniques such as IR, ¹H NMR, ¹³C NMR and mass spectrometry. The structure of products 19, 20, 22, 24 and 25 were also unambiguously confirmed by single crystal X-ray analysis.     

Microwave-assisted synthesis of resorcin[4]arene and pyrogallol[4]arene macrocycles

A series of resorcin[4]arene and pyrogallol[4]arene macrocycles have been synthesized efficiently within 5 min, affording crystalline products suitable for single crystal X-ray diffraction, utilising microwave irradiation in a ‘one-pot’ reaction whilst controlling the selective formation of the rccc cone stereoisomer.     

Synthesis of enantiopure furo[2,3-b]pyrroles

A simple method for the preparation of enantiopure furo[2,3-b]pyrroles, a rare class of concave bicyclic nitrogen and oxygen heterocycle, in promising yield has been developed. The 3-substituted pyrrolidinediones prepared from (2S,3S)-tetrahydro-3-hydroxy-5-oxo-2,3-furandicarboxylic acid (Garcinia acid) have been cyclized diastereo as well as enantioselectively to furo[2,3-b]pyrroles. The cyclization follows Baldwin’s rule.     

A new strategy for the synthesis of pyrazolo[4,3-e][1,2,4]triazolo[4,3-c]pyrimidines and pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidines

A series of pyrazolo[4,3-e][1,2,4]triazolo[4,3-c]pyrimidines were prepared via oxidative cyclization of aldehyde N-(1,3-diphenylpyrazolo[3,4-d]pyrimidin-4-yl)hydrazones. Dimroth rearrangement of such a series yielded pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidines.     

A one-pot,three-component synthesis of spiro[indoline-isoxazolo[4′,3′:5,6]pyrido[2,3-d]pyrimidine]triones in water

A one-pot, three-component condensation reaction of an isatin, isoxazole, and barbituric acid in water to give spirooxindoles in high yields, at 70 °C temperature, using a catalytic amount of p-toluene sulfonic acid, is described.