Stereoselectivity control in the Rh(I)-catalyzed conjugate additions of aryl and alkenylboronic acids to unprotected hydroxycyclopentenones

[reaction: see text] The stereoselective Rh(I)-catalyzed conjugate addition reaction of aryl and alkenylboronic acids to unprotected 2-phenyl-4-hydroxycyclopentenone is presented. The free OH group on the substrate is responsible for the stereochemistry, which is cis for arylboronic derivatives. In the case of the alkenylboronic compounds, the stereochemistry can be tuned to either a cis (bases as additives) or trans addition (CsF as additive) without the need of protecting groups.     

Modeling phase separation and droplet size of W/O emulsions with oregano essential oil as a function of its formulation and homogenization conditions

Oregano essential oil emulsions (W/O) were prepared using different emulsifiers’ blend concentrations of Tween 80/Span 20, to study their phase separation during storage and to optimize the homogenization processing parameters by minimizing the droplet size of emulsions. Phase separation followed a second-order kinetic model, and relationships between the kinetic parameters and the blend concentrations of emulsifiers were established for determining the best emulsion formulations. The instability mechanism of emulsions demonstrated to be Ostwald ripening; therefore, by means of surface response methodology, mechanical homogenization parameters (11,700?rpm for 12 minutes at 1°C) were specified in order to minimize the droplet size of emulsions (1.02?±?0.12?µm).     

2D corrugated magnesium carboxyphosphonate materials: topotactic transformations and interlayer "decoration" with ammonia

In this paper we report the synthesis and structural characterization of the 2D layered coordination polymer Mg(BPMGLY)(H(2)O)(2) (BPMGLY = bis-phosphonomethylglycine, (HO(3)PCH(2))(2)N(H)COO(2-)). The Mg ion is found in a slightly distorted octahedral environment formed by four phosphonate oxygens and two water molecules. The carboxylate group is deprotonated but noncoordinated. This compound is a useful starting material for a number of topotactic transformations. Upon heating at 140 °C one (of the two) Mg-coordinated water molecule is lost, with the archetype 2D structure maintaining itself. However, the octahedral Mg in Mg(BPMGLY)(H(2)O)(2) is now converted to trigonal bipyramidal in Mg(BPMGLY)(H(2)O). Upon exposure of the monohydrate Mg(BPMGLY)(H(2)O) compound to ammonia, one molecule of ammonia is inserted into the interlayer space and stabilized by hydrogen bonding. The 2D layered structure of the product Mg(BPMGLY)(H(2)O)(NH(3)) is still maintained, with Mg now acquiring a pseudo-octahedral environment. All of these topotactic transformations are also accompanied by changes in hydrogen bonding between the layers.     

Synergism in mixtures of n-octyl-β-d-thioglucoside and different n-alkyltrimethylammonium bromides: effect of the alkyl chain length

Mixtures of n-octyl-β-d-thioglucoside with three different n-alkyltrimethylammonium bromides (n?=?12 (DTAB), 14 (TTAB), and 16 (CTAB)) have been studied by using fluorescence spectroscopic techniques. The critical micelle concentration values of pure and mixed systems were determined by the pyrene 1:3 ratio method. The experimental results were treated by using thermodynamic mixing approaches based on the pseudophase separation model. It was found that all the mixed systems show a negative deviation from ideal behavior, more pronounced as the larger the alkyl tail of the co-surfactant. It was also observed that the three mixed systems fulfill the conditions of synergism, this behavior being also dependent on the alkyl chain length. By using the static quenching method, the mean micellar aggregation numbers of mixed micelles were obtained. In all the cases, it was observed that the aggregation number is initially reduced with the participation of the cationic surfactant, remaining almost constant and close to the aggregation number of the pure cationic micelles. The local viscosity of pure and mixed micelles was examined by the photophysical response of the hydrophobic probe coumarin 6 solubilized in the micellar medium. It was found that the participation of the ionic component induces the formation of a less ordered structure than that of pure nonionic micelles. This effect being less pronounced as the chain hydrocarbon length of the co-surfactant increases.     

A Molecular Shuttle Driven by Fullerene Radical‐Anion Recognition

We describe a electrochemically driven molecular shuttle, in which shuttling takes place by means of fullerene radical‐anion recognition that results in a very low operation potential (E_1/2=?0.580 V vs. decamethylferrocene). This has been achieved by introducing positive charges on the macrocycle, which strengthen the existing π–π interactions between the macrocycle and the electrogenerated fullerene radical anion by means of an electrostatic component. In addition, the synthesis of such a molecular shuttle has been accomplished by developing a new synthetic approach that exploits the controlled translocation of the macrocycle as a selective protecting group.     

Rearrangement of oxazolidinethiones to thiazolidinediones or thiazinanediones and their application for the synthesis of chiral allylic ureas and α-methyl-β-amino acids

A novel rearrangement has been found between oxazolidinethiones and acyl halides under N-acylation reaction conditions to afford N-substituted 2,4-thiazolidinediones and N-substituted 1,3-thiazinane-2,4-diones. These heterocycles were used for the synthesis of chiral allylic ureas and α-methyl-β-amino acids.     

Multimode assembly of phenanthroline nanowires decorated with gold nanoparticles

Self-assembled nanohybrids of a 1,10-phenanthroline derivative and Au nanoparticles exhibit different optoelectronic properties, as a consequence of the different arrangements of the nanoparticles on the surface of the different-sized phenanthroline scaffolds.     

Oxazolidine-2-thiones and thiazolidine-2-thiones as nucleophiles in intermolecular Michael additions

Conjugate addition of thiazolidinethiones and oxazolidinethiones to N-crotonylthiazolidinethiones and -oxazolidinethiones was observed in the presence of excess triethylamine in dichloromethane. The addition takes place by the nitrogen of the heterocycle with high diastereoselectivity. It was observed that the stereoselective addition occurs on the anti-s-cis conformation of the N-enoyl sulfur-containing heterocycle.     

Chemoselective aromatic C-H insertion of α-diazo-β-ketoesters catalyzed by dirhodium(II) carboxylates

The ability of α-diazo-β-ketoesters bearing a substituent on the benzylic position to undergo aromatic C-H insertion is described. Good to excellent yields of the aromatic C-H insertion products were observed with Rh(2)(tpa)(4) or Rh(2)(esp)(2) catalysts. This is an attractive strategy to prepare tetralins carrying a methyl group on the benzylic position, a structural motif found in several types of natural products.