Modification of chitosan with ethoxycarbonyl and 3-fluoroimidazo[1,2-<Emphasis Type="Italic">a</Emphasis>]pyridine-2-carbonyl fragments

Reactions of the natural biopolymer chitosan with 3-fluoroimidazo[1,2-a]pyridine-2-carboxylic acid hydrochlorides in the presence of ethyl 2-ethoxy-1,2-dihydroquinoline-1-carboxylate resulted in introduction of ethoxycarbonyl and 3-fluoroimidazo[1,2-a]pyridine-2-carbonyl fragments into glucosamine units of the polymer.     

Preparation of novel pyridine-fused tris-heterocycles; pyrido[4,3-e]pyrrolo-/pyrido[4,3-e]furano[2,3-c]pyridazines and pyrido[3,4-b]pyrrolo[3,2-d]pyrrole

Three novel pyrido-fused tris-heterocycles have been prepared based on a Suzuki coupling and subsequent cyclisation approach. Pyrido[4,3-e]pyrrolo[2,3-c]pyridazine (3b, 77%) and pyrido[4,3-e]furano[2,3-c]pyridazine (5b, 76%) were obtained by intramolecular diazocoupling. Successful diazocoupling of furan (5b) is thus reported for the first time by NOBF₄ generation of the diazonium intermediate. N-TIPS-pyrido[3,4-b]pyrrolo[3,2-d]pyrrole (TIPS-4b) was synthesised by thermal cyclisation of pyridyl nitrene in considerably higher yield (71%) than previously experienced from similar cyclisations, due to TIPS-activation.     

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.     

Synthesis and rearrangement of cycloalkyl[1,2-e]oxazolo[3,2-a]pyrimidin-8/9-ones: an access to cycloalkyl[1,2-d]oxazolo[3,2-a]pyrimidin-5-ones

2-Substituted-4a-hydroxy-9H-cycloalkyl[1,2-e]oxazolo[3,2-a]pyrimidin-9-ones 2a-c were synthesized by an one-step cyclocondensation from the 5-substituted-2-amino-2-oxazolines 1a-c with ethyl 2-oxocyclohexanecarboxylate in ethanol at room temperature, and easily dehydrated to provide 2-substituted-9H-cycloalkyl[1,2-e]oxazolo[3,2-a]pyrimidin-9-ones 3. In refluxing xylene, the reaction conducted with various ethyl 2-oxocycloalkanecarboxylates led to the two isomeric 2-substituted-8/9H-cycloalkyl[1,2-e]oxazolo[3,2-a]pyrimidin-8/9-ones 3 and 2-substituted-5H-cycloalkyl[1,2-d]oxazolo[3,2-a]pyrimidin-5-ones 4. The structure of some compounds was unambiguously established using X-ray crystallography. According to results from the DSC analysis of compound 2a, formation of the thermodynamically stable pyrimidinones 4 could be related to an intramolecular rearrangement of kinetically controlled pyrimidinones 3.     

Cyclisation of 3-alkenylpyrido[1,2-a]pyrimidines to furo[2,3-d]pyrido[1,2-a]pyrimidines

3-Alkenylpyrido[1,2-a]pyrimidines react under mild conditions to give novel tricyclic furo[2,3-d]pyrido[1,2-a]pyrimidines in high yields. The cyclisation takes place in the presence of an acid catalyst. The product yield is affected by the type and the strength of the acid used. Exceptionally high yields were obtained when an organic acid like trifluoromethanesulfonic acid and trifluoroacetic acid were used. On the other hand, sulfuric acid gave the best results of the inorganic acids examined.     

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.     

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.     

Convenient synthesis of fused pyrano[3,2-h]- and furo[3,2-h]benzo[f]coumarins from naphthalene-2,3-diol

The treatment of 8-propargyloxy-benzo[f]coumarin with boron trifluoride diethyl etherate in N,N-dimethylformamide under reflux or MW irradiation resulted in pyrano[3,2-h]benzo[f]coumarin, while the furo[3,2-h]benzo[f]coumarin is received from the treatment with N-methylformamide under MW irradiation.     

Chemical reactivity of [1,2,3]triazolo[1,5-a]- and [1,5-c]-pyrimidinium salts

The chemical reactivity of the [1,2,3]triazolo[1,5-a]- and [1,5-c]-pyrimidinium salts towards morpholine, water and sodium methoxide have been studied. Among others, new 1-aza and 2-azabutadienes substituted by a [1,2,3]-triazole ring were obtained in the course of the opening of the positively charged pyrimidine ring.     

Regioselective formylation of pyrazolo[3,4-b]pyridine and pyrazolo[1,5-a]pyrimidine systems using Vilsmeier-Haack conditions

Regioselective formylation behavior has been found in the reaction of pyrazolo[3,4-b]pyridines and pyrazolo[1,5-a]pyrimidines via Vilsmeier-Haack conditions. While the 4,5- and 6,7-dihydro derivatives afforded pyrazolo[3,4-b]pyridine-5-carbaldehydes and 4,7-dihydropyrazolo[1,5-a]pyrimidine-3,6-dicarbaldehydes, respectively, the aromatic analogs rendered the pyrazolo[1,5-a]pyrimidine-3-carbaldehyde only, and no reaction took place at the pyrazolopyridine derivatives.     

Short and efficient access to imidazo[1,2-a]pyrrolo[3,2-c]pyridine derivatives

Access to N-protected or N-free imidazo[1,2-a]pyrrolo[3,2-c]pyridine derivatives as potential antiviral compounds was achieved in good yields from N-protected 7-amino-8-halo-2-methylimidazo[1,2-a]pyridines by catalytic coupling of terminal acetylenes under mild conditions using [PdCl₂(PPh₃)₂] or [Cu(Phen)(PPh₃)₂]NO₃.     

Synthesis of novel fluorescent benzo[a]pyrano[2,3-c]phenazine and benzo[a]chromeno[2,3-c]phenazine derivatives via facile four-component domino protocol

An efficient and practical route to novel fluorescent benzo[a]pyrano[2,3-c]phenazine framework has been developed by one-pot, four-component reaction of 2-hydroxynaphthalene-1,4-dione, 1,2-phenylenediamines, aromatic aldehydes, and Meldrum’s acid in glacial acetic acid at 70 °C. Photophysical studies of these compounds have been reported. Reactions involving cyclohexane-1,3-dione/5-methylcyclohexane-1,3-dione/dimedone in the place of Meldrum’s acid yielded corresponding benzo[a]chromeno[2,3-c]phenazine derivatives. Crystal structure of 3k established the regioisomer formed. Mild reaction conditions, good yields, short reaction time, and easy separation are some of the salient features of the present protocol.     

A modular approach to 4,5-diaminopyrrolo[2,3-d]pyrimidines and 2,4,5-triaminopyrrolo[2,3-d]pyrimidines

A short and highly modular approach to various 4,5-diaminopyrrolo[2,3-d]pyrimidines and 2,4,5-triaminopyrrolo[2,3-d]pyrimidines was developed starting from 4-chloro-5-halopyrrolo[2,3-d]pyrimidines and 5-bromo-2,4-dichloropyrrolo[2,3-d]pyrimidine, respectively. Direct amination at the 5-position was achieved without the use of transition metals or other catalysts in 32-86% yield. Ten examples are given.     

Intramolecular 4+2 cycloaddition of thieno[2,3-e][1,2,4]triazines: routes towards condensed thieno[2,3-b]pyridines

Synthetic approaches towards new condensed thienopyridine ring systems including furo[2,3-b]thieno[3,2-e]pyridines, bisthieno[2,3-b:3′,2′-e]pyridines, 5H-chromeno[2,3-b]thieno[3,2-e]pyridines, 5H-benzo(f)chromeno[2,3-b]thieno[3,2-e]pyridines have been achieved by application of intramolecular 4+2 cycloaddition reactions of suitably designed thieno[2,3-e][1,2,4]triazines tethered with alkene or alkyne terminals.     

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.     

An efficient synthesis of novel estrieno[2.3-b] and [3.4-c]pyrroles

An efficient protocol for the preparation of novel estrieno[2.3-b] and [3.4-c]pyrroles 1 and 2 using Pd(0)-catalyzed amination and Bischler indole synthesis is described.     

One-step synthesis of [1]benzothieno[3,2-b][1]benzothiophene from o-chlorobenzaldehyde

Simple one-step synthesis of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) from commercially available o-chlorobenzaldehyde is reported. The procedure is also applicable to the synthesis of dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT).     

Solid-phase synthesis of imidazo[1,2-a]pyridines and imidazo[1,2-a]pyrimidines

The synthesis of imidazo[1,2-a]pyridine and imidazo[1,2-a]pyrimidine derivatives by condensation between an α-bromoketone bound to solid support and various 2-aminopyridine or 2-aminopyrimidine derivatives was described. Either an acid labile linker or a base labile linker was used in this study.     

Microwave-assisted synthesis of novel N-(4-phenylthiazol-2-yl)-benzo[d]thiazole-, thiazolo[4,5-b]pyridine-, thiazolo[5,4-b]pyridine- and benzo[d]oxazole-2-carboximidamides inspired by marine topsentines and nortopsentines

We report the synthesis of novel N-(4-phenylthiazol-2-yl)-substituted benzo[d]thiazole-, thiazolo[4,5-b]pyridine-, thiazolo[5,4-b]pyridine- and benzo[d]oxazole-2-carboximidamides, which were inspired by marine topsentines and nortopsentines. Condensation of 4,5-dichloro-1,2,3-dithiazolium chloride (Appel salt) with various ortho-halogenated anilines, aminopyridines and aminophenols gave the corresponding aryliminodithiazoles in good to excellent yields. Copper(I)-mediated or nucleophilic-assisted cyclization of aryliminodithiazoles furnished cyano-functionalized benzo[d]thiazoles, thiazolo[4,5-b]- and thiazolo[5,4-b]-pyridines and benzo[d]oxazoles. The latter were condensed with substituted 4-phenylthiazol-2-amines to furnish twenty seven new polyaromatic carboximidamides in moderate to good yields.     

A simple method for the preparation of selenopheno[3,2-b] and [2,3-b]thiophenes

A simple strategy for the preparation of novel selenopheno[3,2-b] and [2,3-b]thiophenes by treatment of ethynylthiophenes with selenium(I), (II), and (IV) chlorides and bromides is elaborated.