Béchir Ben Hassine

Eco‐Friendly Solvents for Palladium‐Catalyzed Desulfitative CH Bond Arylation of Heteroarenes

Herein, we report the Pd-catalyzed regioselective direct arylation of heteroarenes in which benzenesulfonyl chlorides are used as coupling partners through a desulfitative cross-coupling that can be performed in diethyl carbonate (DEC) or cyclopentyl methyl ether (CPME) as green and renewable solvents or even in neat conditions instead of dioxane or dimethylacetamide (DMA). Under these solvent conditions, the reaction proceeds with a wide range of heteroarenes. C2- or C5-arylated products were obtained with furan and pyrrole derivatives. Benzofuran was also arylated regioselectively at the C2-position, whereas the reaction proceeds selectively at the C3- or C4-positions if thiophenes and benzothiophenes are used. Moreover, in some cases, especially with 1-methylindole, solvent-free conditions afforded better regioselectivities and/or yields than the reaction performed in the presence of solvents.

Synthesis and pharmacological profile of 6-methyl-3-isopropyl-2H-1,2-benzothiazin-4(3H)-one 1,1-dioxide derivatives: non-steroidal anti-inflammatory agents with reduced ulcerogenic effects in the rat.

The new anti-inflammatory agents 6-methyl-3-isopropyl-2H-1,2-benzothiazin-4(3H)-one 1,1-dioxide 6a and its analogues 6b-f were synthesized from L-valine. All compounds were characterized by physical, chemical and spectral studies. Preliminary pharmacological evaluation of the resulting products showed that compounds 6a-f (5-20 mg/kg, i.p.) are active anti-inflammatory agents in carrageenan-induced rat paw oedema assay in albino rats, and their effects are comparable to that of piroxicam (5 mg/kg, i.p.), used as a reference drug. The nature of the substituents on the sulfonamide nitrogen and those on position three had a pronounced effect on the anti-inflammatory activity. Studies of structure-activity relationships have led to selection of compound 2,6-dimethyl-3-isopropyl-1,2-benzothiazin-3,4-diol 1,1-dioxide 6 f which exhibited the most potent activity (61.7% inhibition at 5 mg/kg, i.p. and ED(50)=4.5 mg/kg, i.p.). Comparison of the gastrointestinal safety of compounds 6a-f with that of piroxicam showed a far better tolerability for our products. This comparison was based on the ulcer index and the pH of gastric content.

STEREOSPECIFIC SYNTHESIS OF 2-ALKYL-3-ARYLOXAZIRIDINES FROM PROCHIRAL AND CHIRAL N-ARYLIDENEALKYLAMINES BY USE OF THE BENZONITRILE-HYDROGEN PEROXIDE SYSTEM

Benzonitrile-hydrogen peroxide oxidation of prochiral and chiral imines 1a–h leads to racemic (E)-oxaziridines (R,R/S,S) and nonracemic (E)-oxaziridines (R,R,R/S,S,R) 2a–h, respectively.

Synthesis and X‐Ray Analysis of a New [6]Helicene

Abstract A new disubstituted hexahelicene derivative 3 bearing methoxy functions at positions 3 and 14 has been prepared in racemic form through a Heck reaction followed by photocyclodehydrogenation. Suitable crystals of rac‐3 were analyzed by X‐ray crystallography and showed similar geometry to the structure of hexahelicene itself. Deprotection of 3 using boron tribromide led to 3,14‐dihydroxyhexahelicene 4 in quantitative yield. The complexation of transition metal atoms seemed to be quite possible by these two bidentate hexahelicene derivatives.

New chitosan microspheres supported [bis(2-methylallyl)(1,5-cyclooctadienne)ruthenium(II)] as efficient catalysts for colour degradation in the presence of hydrogen peroxide

This paper concerns the immobilisation of either [bis(2-methylallyl)(1,5-cyclooctadienne)ruthenium(II)] (I) or ruthenium chloride (RuCl3) (II) on chitosan microspheres (catalyst I and catalyst II, respectively). These heterogenised catalysts were used for the oxidative degradation of two acid dyes, i.e. [Calmagite (Calma) and Acid Blue 25 (AB25)] in aqueous solution at pH 7.0 in the presence of hydrogen peroxide (H2O2). Prepared solid supports were characterised by Fourier transform infrared (FTIR) spectral study, thermogravimetry (TG), differential thermogravimetry (DTG) and differential scanning calorimetry (DSC) analyses. The efficiency of decolourisation was justified using UV–visible spectroscopic analysis. The factors affecting dye degradation were studied. Some tests for Calma decolourisation achieved up to 100% colour removal using catalyst I. The pseudo first-order equation was shown to fit degradation kinetics in most cases. However, for some cases, it was necessary to use a reversible equation. The energetic parameters were determined and the activation energy (E a) was found to be low, between 11 and 36 kJ mol−1, confirming that these catalysts were very efficient for the degradation of anionic dyes using H2O2. The interpretation of the equilibrium sorption data complies well with the Freundlich adsorption model. The combination of adsorption process and catalytic oxidation made the new developed catalyst systems to achieve a simple and efficient water treatment.

Synthesis of new 1,2,4-oxadiazolidin-3-ones by cycloaddition of 2-alkyl-3-aryloxaziridines with chlorosulfonylisocyanate

Abstract 2-Alkyl-4-chlorosulfonyl-5-aryl-1,2,4-oxadiazolidin-3-ones 5 were prepared via cycloaddition of 2-alkyl-3-aryloxaziridines 3 with chlorosulfonylisocyanate. The structure of 5 was proved by a crystal X-ray analysis. Hydrolysis of 5 in the presence of triethylamine afforded 2-alkyl-5-aryl-1,2,4-oxadiazolidin-3-ones 6 .

Conditions for palladium-catalyzed direct arylations of 4-bromo and 4-iodo N -substituted pyrazoles without C–Br or C–I bond cleavage

The Pd-catalyzed arylation at the C5 position of N-protected pyrazole derivatives bearing bromo or iodo substituents at the C4 position is described. A simple phosphine-free catalytic system was used, namely, 1 mol% Pd(OAc)2 in DMA in the presence of KOAc as the base. A wide aryl bromide scope as a coupling partner has been coupled with pyrazole derivatives. The reaction was very chemoselective as the C–halogen bonds of the pyrazole units were not involved in the C–H bond arylation process. Some examples demonstrating the synthetic potential of the bromo and iodo pyrazole substituents for chemical transformations are reported.

A comparative study on the performance of dye removal, from aqueous suspension, using (2-hydroxypropyl)-β-cyclodextrin-CS, PVP-PVA-CS, PVA-CS, PVP-CS and plain CS microspheres

This paper reports the results of the study on the performance of the removal of Cibacron Brilliant Yellow 3G-P and Calmagite, from aqueous solution, using either prepared 2-hydroxypropyl-β-cyclodextrin-chitosan [HPβCD-CS], poly(vinylalcohol)-polyvinylpyrrolidone-chitosan [PVA-PVP-CS], Poly(vinylalcohol)-chitosan [PVA-CS], polyvinylpyrrolidone-chitosan [PVP-CS] or plain chitosan microspheres [CS]. Modified CS molecules were analysed using FT-IR and TG-DTA techniques. Adsorption experiments were carried out and compared through varying mass ratio, contact time, initial dye concentration and temperature. Among the five studied adsorbents, the highest adsorption capacity was reached using HPβCD-CS. Kinetic equations were applied and the first-order model was shown to fit the adsorption phenomenon. The applicability of Langmuir, Freundlich, Temkin and Dubinin–Radushkevich equations was tested and the Langmuir isotherm exhibited the best fit with the experimental data. Data gleaned from both modelling and thermodynamic results indicate that the adsorption follows a physical and exothermic process.

Synthesis and Characterization of a New Racemic Helically Chiral Ru(II) Complex and Its Catalytic Degradation of Eriochrome Blue Black B

Abstract A new helically chiral ruthenium complex of fused aromatic rings was prepared in a one stepsequence and fully characterized. The new complex was used as an heterogeneous catalyst for the degradation of Eriochrome Blue Black B (one of the azoic dyes) in aqueous medium in the presence of hydrogen peroxide. Using a fixed dose of H2O2, experiments revealed that the dye degradation was affected by the reaction temperature and the initial dye concentration. The energetic parameters were also determined, and the activation energy (E a) was found to be low (31 kJ mol−1), confirming that the prepared catalyst was very efficient for the degradation of anionic dyes using H2O2. The complex exhibited excellent catalytic activity and has the advantage of easy separation from the reaction medium. In addition, the ruthenium helical complex–H2O2 system could remain with good catalytic activity after five cycles. GRAPHICAL ABSTRACT

Synthesis of new 3-substituted-2H-1,2-naphthothiazin-4(3H)-one 1,1-dioxides via directed ortho-metalation reaction

Abstract The reaction of compounds 6a – i , readily available from α-amino acids, with an excess of lithium diisopropylamide, leads to new 3-substituted-2 H -1,2-naphthothiazin-4(3 H )-one 1,1-dioxides 7a – i , with yields ranging between 21 and 70%. The key steps are: the naphthylsulfonyl ortho-deprotonation based on the directed ortho-metalation reaction followed by a regiospecific intramolecular cyclisation reaction. Lithiation–deuteration experiments carried out on the naphthylsulfonamides 8 and 9 using n -BuLi and LDA demonstrated the regioselectivity of the deprotonation of the H-3 over the H-1 one of the naphthalene ring.