Ridha Ben Salem

Effect of pressure on the Strecker synthesis of hindered α-aminonitriles from ketones and aromatic amines

Abstract The effect of high pressure is examined in Strecker reactions involving ketones, amines and trimethylsilyl cyanide. This effect is small when moderately hindered reactants are involved. However, in the case of aniline and N -methylaniline, the sensitivity of the reaction to pressure increases with increasing steric bulk of the alkyl groups of the ketone. The results confirm the merit of pressure activation as sterically demanding reactions are subject to higher pressure acceleration than their unhindered analogs.

Ultrasonic activation of Heck type reactions in the presence of Aliquat-336

Without phosphine and base, palladium catalysts such as PdCl(2), Pd(OAc)(2) and PdCl(2)(PhCN)(2) in water/DMF mixtures with Aliquat-336 proved to be excellent catalytic systems for Heck reactions involving several aryl bromides with styrene and acrylic compounds. Yields are remarkably improved under ultrasonic irradiation and the products show a high purity.

Phenolic Composition, Isolation, and Structure of a New Deoxyloganic Acid Derivative from Dhokar and Gemri‐Dhokar Olive Cultivars

Two rare olive cultivars, Dhokar and Gemri-Dhokar, growing in the south of Tunisia were investigated to identify their phenolic profile and evaluate their sugar content and antioxidant activity. The highest value of phenolic content was detected in Gemri-Dhokar cultivar extract (6.97 g gallic acid equivalents/kg of fresh olive). In addition, sugar content was quantified; glucose (45.17 g/kg of fresh olive) was the predominant sugar in Dhokar cultivar, followed by fructose (40.83 g/kg of fresh olive). The identification of phenolic compounds was based on separation by high-performance liquid chromatography equipped with a diode array detector followed by liquid chromatography-mass spectrometry analysis. In both cultivars, Oleuropein aglycon derivatives and elenolic acid were the main phenolic components. Oleuropeins were the major compounds quantified in the Gemri-Dhokar drupes olives (61.04 mg/100 g of fresh olive), while 0.25 mg/100 g were found in fresh Dhokar. A new iridoid compound, isolated as pure compound, was not previously reported in the literature. Its structure was established by spectroscopic analyses (NMR, UV, MS, and IR). DPPH, ABTS, and FRAP assays showed that the most important antioxidant capacity of olive extracts was found in with Gemri-Dhokar cultivar.

The cause of the rate acceleration by diethyl ether solutions of lithium perchlorate (LPDE) in organic reactions. Application to high pressure synthesis

Abstract Kinetic studies of isoprene cyclodimerization show that the accelerating effect caused by LPDE (solution of lithium perchlorate in diethyl ether) in some organic reactions cannot be ascribed to internal pressure of LPDE. The kinetic effect is essentially due to catalysis through Li+. Additional arguments are provided by comparison of yields obtained in LPDE (0,1 MPa) and in organic solvents (under pressure) for Diels-Alder reactions of various electronic types. Combination of high pressure and LPDE catalysis is revealed as an excellent multiactivation process to achieve difficult syntheses, but only for [4+2] cycloadditions.

Analytical evaluation of two monovarietal virgin olive oils cultivated in the south of Tunisia: Jemri-Bouchouka and Chemlali-Tataouin cultivars

BACKGROUND The characterisation of virgin olive oils from two Tunisian cultivars, growing in the Tataouin zone, namely Jemri-Bouchouka, a rare olive cultivar, and Chemlali-Tataouin, was carried out. Several analytical parameters were evaluated; these include quality index, fatty acids, phenolic, chlorophyll, carotenoid, squalene, α-tocopherol compositions and oxidative stability. RESULTS Jemri-Bouchouka olive oil had the highest value of oleic acid (74.50%) while Chemlali-Tataouin olive oil had the highest value of oleic acid (69.39 %) and also was characterized by a high percentage of palmitic acid (14.75 %) which makes this oil freeze at a low temperature [corrected]. On the other hand, Jemri-Bouchouka oil was characterised by a low phenolic and α-tocopherol content (267.72 mg GAE kg⁻¹ and 278.34 mg kg⁻¹, respectively). Ten phenolic compounds were identified. The main phenols found in the two olive oils were oleuropein aglycon and pinoresinol. All phenolic compounds showed significant correlations with oxidative stability. CONCLUSION The analytical parameters of virgin olive oil that were determined in this study were greatly influenced by cultivar.

Kinetic effects in water and ethylene glycol. Application to high pressure organic synthesis

The kinetic effect of various Diels–Alder and Michael reactions is studied in water and ethylene glycol vs. organic solvents. The rate enhancement is considerable in water, much less in ethylene glycol. It is proposed that strong solvophobic interactions operate in water whereas the kinetic results in glycol are best explained by hydrogen bonding and polarity effects. From a synthetic point of view, use of the properties of water (hydrophobic interactions) or ethylene glycol (ionogenic medium) associated with the kinetic effect of high pressure may constitute an interesting multiactivation method to increase chemical reactivity. Examples of triactivation (high pressure catalytic Diels–Alder reactions in ethylene glycol) are given.

Anatomy of ene and Diels–Alder reactions between cyclohexadienes and azodicarboxylates

In contrast with other (C ⋯ H ⋯ N) hydrogen transfers, the high-pressure kinetics of the ene reaction between cyclohexa-1,4-diene and diethyl azodicarboxylate show a concerted transition state. The discrepancy is assigned to the enhanced rigidity of the cyclohexadiene molecule with orthogonal hydrogen transfer to the nitrogen atom. Cyclohexa-1,3-diene reacts with diethyl azodicarboxylate according to a concerted Diels–Alder reaction.

Identification and characterization of a new iridoid compound from two-phase Chemlali olive pomace

From ethyl acetate fraction of olive pomace, solid residue from olive oil extraction, a new compound was isolated and purified through solid-phase extraction using silica Cartridge column chromatography. The structure of the new compound was established as a deoxyloganic acid lauryl ester by spectroscopic data including one- and two-dimensional NMR, electrospray ionization mass spectrometry, infrared analysis and UV spectra. The antioxidant activity of the purified compound was evaluated by measuring the radical-scavenging effect on 2,2-diphenyl-1-picrylhydrazyl and by using the ferric reducing antioxidant power assays. The pure compound has not been previously identified in the genus Olea and could be used as for studying the biosynthetic pathway of oleuropein aglycon.

Unprecedented access to ‐arylated selenophenes via palladium‐catalysed direct arylation

Several reported methods allow access to α-arylated selenophenes, whereas the synthesis of β-arylated selenophenes remains very challenging. Here, the Pd-catalysed coupling of benzenesulfonyl chlorides with selenophenes affording regiospecific β-arylated selenophenes is reported. The reaction proceeds with easily accessible catalyst, base and substrates, and tolerates a variety of substituents both on the benzene and selenophene moieties. This transformation allows the programmed synthesis of polyarylated selenophenes with potential applications in pharmaceutical and materials chemistry, as the installation of aryl groups at the desired positions can be achieved.

Access to (Hetero)arylated Selenophenes via Palladium-catalysed Stille, Negishi or Suzuki Couplings or C−H Bond Functionalization Reaction

(Hetero)aryl‐substituted selenophenes exhibit important physical properties especially for optoelectronics. Palladium‐catalysed coupling reactions currently represent the most efficient methods to prepare such (hetero)arylated selenophene derivatives. Initially, Stille coupling was the most efficient reaction for the synthesis of these compounds; however, over the last decade, Suzuki coupling has become the most commonly employed. Recently, Pd‐catalysed arylation via the C−H bond activation of selenophenes has proved to be a very convenient alternative method for the preparation of several arylated selenophenes as there is no need to prepare organometallic derivatives. In this Review, the progress and substrate scope in the synthesis of both C2‐ and C3‐arylated selenophenes via Pd‐catalysis are summarized.