Synthesis and mechanistic studies on the aquation of selenitoaquobis(diamine)cobalt(III) complexes

Summary The kinetics of the aquation of four selenitoaquobisdiamine)cobalt(III) complexes to their respective diaquabis-(diamine)complexes (diamine=ethylenediamine en, propylenediamine pn, dimethylethylenediamine me₂en and trimethylenediamine tmd) have been carried out conductimetrically in the 25–45 °C range. All reactions exhibit simple first order kinetics, and the rates increase with increasing temperature. In aqueous solution, the complex species exist in equilibrium with their respective hydroxo species, but only the hydroxo species are involved in the aquation process. This result is also reflected in the linear Arrhenius plot. The rates are higher in a 10% alcoholic solution than in water, but then decrease with increase in the alcohol content. A Grunwald-Winstein plot of rates in methanol yields slopes of 0.18 ± 0.04, 0.27±0.03, 0.43±0.03 and 0.34±0.02 for the four amines respectively. A dissociation mechanism is proposed for the aquation of all these complexes.     

Highly effective peroxidic epoxidation of olefins using hexathiocyanatorhenate(IV) as catalyst and bicarbonate as co-catalyst

In the presence of bicarbonate as co-catalyst hexathiocyanatorhenate(IV) functions as an extremely effective catalyst in the epoxidation of olefins using aqueous hydrogen peroxide as the terminal oxidant.     

Iodine-catalyzed efficient conjugate addition of pyrroles to α,β-unsaturated ketones

Iodine was used as a catalyst for the conjugate addition of pyrroles to α,β-unsaturated ketones at room temperature. Mono- and dialkylated products were obtained by using equimolar amounts of the reactants. However, the use of excess enones afforded only dialkylated products.     

Jatrophenone,a novel macrocyclic bioactive diterpene from Jatropha gossypifolia

A novel macrocyclic diterpene, jatrophenone, has been isolated from the whole plant of Jatropha gossypifolia. The structure of the compound was established by detailed studies of its one- and two-dimensional (1D and 2D) NMR spectra. The compound possesses significant antibacterial activity.     

Kinetics and mechanisms of the reactions of thiosulphato-amine complexes of cobalt(III). Part II. Base hydrolysis of the bis(ethylenediamine)thiosulphatocobalt(III) ion

Summary Base hydrolysis of the bis(ethylenediamine)thiosulphatocobalt(III) was investigated spectrophotometrically between 35 and 65 °C and with base concentrations (NaOH) up to 2.0 mol dm^–3. The hydrolysis consists of a one-stage reaction, followed by a slow dechelation step, and then by a fast ligand loss. The reaction is base-dependent. The products of the reaction are an equilibrium mixture ofcis- andtrans-Coen₂ (OH) ₂ ⁺ . Activation parameters for the reaction as determined by the Eyring equation, are H=77.8±4.6 kJ mol^–1 and S=–75±20 JK^–1 mol^–1.     

Stereoselective total synthesis of (+)-strictifolione and (6R)-6[(E,4R,6R)-4,6-dihydro-10-phenyl-1-decenyl)-5,6-dihydro-2H-2-pyrone

The stereoselective total synthesis of two naturally occurring α-pyrone derivatives, (+)-strictifolione and (6R)-6[(E,4R,6R)-4,6-dihydroxy-10-phenyl-1-decanyl]-5,6-dihydro-2H-2-pyrone has been accomplished involving the Sharpless kinetic resolution and olefin cross-metathesis as the key reactions.     

Effect of the composition of lecithin/n-propanol/isopropyl myristate/water microemulsions on barrier properties of mice skin for transdermal permeation of tetracaine hydrochloride: in vitro

Effect of composition of lecithin water-in-oil and oil-in-water microemulsion on in vitro transdermal permeation of tetracaine hydrochloride was studied on mice model. The results were compared with an aqueous solution of tetracaine hydrochloride (2.7 mg/ml). In vitro skin flux and permeability coefficients were obtained using the Franz diffusion cell. Differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM) were used to study the mechanism of action of the microemulsion. Micrographs of TEM and CLSM studies were analyzed by using Image Pro Plus image software. Skin flux of tetracaine hydrochloride was found to be dependent on the composition of lecithin/n-propanol/isopropyl myristate/water microemulsions. At lower Km ratio (i.e. 0.5:1 and 0.8:1) of microemulsion, the rate of permeation of tetracaine hydrochloride was higher when compared to the microemulsion of higher Km ratio (1:1 and 1.5:1). Image analysis of TEM micrograph, 6h after application of lecithin microemulsion, showed 3.5+/-0.75-fold (p<0.001) increase in the intercellular space in the epidermis and 3.8+/-0.4-fold (p<0.001) enhancement in upper dermis. CLMS results show that sweat gland and hair follicles also provided path for permeation of the drug through the skin.     

A Mild and Efficient Method for Chlorination of Baylis–Hillman Adducts Using PPh3/Cl3CCONH2

A new and convenient stereoselective synthesis of (Z)‐2‐(chloromethyl)alk‐2‐enoates has been achieved from Baylis–Hillman adducts by treatment with PPh₃/Cl₃CCONH₂ at room temperature. The synthesis can proceed under mild and acid‐free conditions to form the products in high yields.     

A convenient highly stereoselective synthesis of allyl amides from Baylis–Hillman adducts using Amberlyst-15 as a heterogeneous reusable catalyst

The Baylis–Hillman adducts have efficiently been converted into the corresponding allyl amides in stereoselective manner by heating in acetonitrile under reflux in the presence of Amberlyst-15 as a catalyst. The catalyst works under heterogeneous conditions and can be recycled.     

An efficient synthesis of benzyl bromides from aromatic aldehydes using polymethylhydrosiloxane and (bromodimethyl)sulfonium bromide or N-bromosuccinimide

Polymethylhydrosiloxane (PMHS) in combination with (bromodimethyl)sulfonium bromide or NBS has been utilized for the first time for reductive bromination of aromatic aldehydes at room temperature to afford the corresponding benzyl bromides in excellent yields.