Rh-Catalyzed asymmetric hydrogenation of (Z)-ethyl 3-acetamido-2-butenoate in supercritical carbon dioxide: the effect of cosolvents

Rh-Catalyzed asymmetric hydrogenation (up to 85% ee) of (Z)-ethyl 3-acetamido-2-butenoate was carried out for the first time in supercritical CO₂ using protic cosolvents. The activity of the Rh catalyst bearing the amidophosphite ligand increases with an increase in acidity of the protic cosolvents and with hydrogen pressure.     

Interpretation of vibrational spectra of a closed form of indoline spirophenanthroxazine

We have measured IR and Raman spectra of molecules of a closed form of the photochromic compound indolinespirophenanthroxazine. Using the density-functional method, we have optimized the structures of the closed and open forms of this molecule and calculated its normal vibrations. Based on these calculations, we propose an interpretation of the obtained vibrational spectra. We have determined the spectral range of manifestation, 700–900 cm^?1, and have found wavenumbers of normal vibrations through which the spiro structure of the indolinespirophenanthroxazine molecule in an excited state is likely to be rearranged into a merocyanine structure.     

Asymmetric iridium-catalyzed hydrogenation of 2-methylindole using phosphite ligands

The iridium-catalyzed asymmetric hydrogenation of 2-methylindole using monodentate phosphites and amidophosphites as ligands was examined. The use of iodine as the additive resulted in increased enantioselectivity and conversion in the iridium-catalyzed hydrogenation of 2-methylindole. Full conversion and up to 80% ee were obtained with a catalyst based on a phosphite ligand.     

A P-chiral bisdiamidophosphite ligand with a 1,4:3,6-dianhydro-d-mannite backbone and its application in asymmetric catalysis

A novel readily available P,P-bidentate diamidophosphite ligand with P^∗-stereocentres is prepared from an inexpensive C₂-symmetric 1,4:3,6-dianhydro-d-mannite. By using this efficient ligand, up to 98% ee is achieved in Pd-catalysed asymmetric allylic alkylation, up to 92% ee in Pd-catalysed asymmetric allylic amination and up to 87% ee in Rh-catalysed asymmetric hydrogenation. The influence of the precatalyst, substrate and solvent on the enantioselectivity is discussed.     

Resonance compression of an acoustic beam in a crystal

The resonance excitation of an intense acoustic beam in a crystal is described for a special geometry of pump-wave reflection from the crystal surface. The resonance appears in the vicinity of the total internal reflection angle under the condition that the wave field in a compressed reflected beam propagating almost parallel to the surface is close to the volume eigenmode satisfying the free boundary condition. Criteria for the existence of such modes are considered in detail. Conversion conditions are analyzed under which a “parasitic” reflected wave of the same branch as the incident wave is absent and entire energy from the incident wave falls within a narrow intense acoustic beam of another branch. It is shown that, when the surface is chosen parallel to the crystal symmetry plane, the conversion criterion is reduced to the sole condition on the elastic moduli of the medium. Analysis is performed by analytic and numerical methods for skew cuts of monoclinic, rhombic, trigonal, and hexagonal crystals, when the boundary is the symmetry plane, while the sagittal plane has no symmetry. A number of crystals are found in which resonance excitation is very close to conversion.     

Diastereomeric P*-mono- and P*,P*-bidentate diamidophosphite ligands based on 1,4:3,6-dianhydro-d-mannitol in asymmetric metallocomplex catalysis

Synthesis of diastereomeric mono- and bidentate diamidophosphites bearing P*-stereo-centers and phosphabicyclo[3.3.0]octane backbone and their coordination with rhodium(i) and palladium(ii) are considered. Their use in Rh-catalyzed asymmetric allylation allowed one to achieve 87% ee values and the use in Rh-catalyzed asymmetric hydrogenation gave up to 98% ee.     

Hydroformylation of alkenes in supercritical carbon dioxide catalyzed by rhodium complexes with amidophosphite derivatives of carboranes

New carborane-containing amidophosphites are synthesized. Their effectiveness as ligands in the Rh-catalyzed hydroformylation of alkenes in supercritical carbon dioxide (SC-CO₂) is tested. It is shown that the use of carboranylamidophosphites makes it possible to achieve a high degree of conversion at a low catalyst loading. In the SC-CO₂ medium, the regioselectivity is higher as compared to the toluene medium.     

Cymantrene-derived monodentate phosphites: New ligands for Rh-catalyzed enantioselective hydrogenation

Novel chiral monodentate phosphite ligands bearing cymantrene fragment have been prepared. Phosphite 4 with PPh₃, instead of CO-ligand, in cymantrene moiety provided higher enantioselectivity than its unsubstituted analogue 3 in hydrogenation of (Z)-methyl-2-acetamido-3-phenylacrylate.     

Numerical Simulation of a Liquid Drop Freely Oscillating

Free oscillations of a viscous liquid drop surrounded by a dynamically inactive ambient gas, in zero gravity, are investigated numerically using FIDAP^TM package in the axisymmetrical case. The full Navier‐Stokes equations with appropriate interfacial conditions are solved by using Galerkin/Finite element technique along with the spine method for the advection of the free boundary are used. The aim of this preliminary study is to demonstrate the ability of the package to accurately solve nonlinear free surface problems. Oscillations of viscous drops released from an initial static deformation of small‐ to large‐amplitude proportional to the second spherical harmonic, without initial internal circulation, are considered. Accuracy is attested by demonstrating that (i) the drop volume remains constant, (ii) dynamic response to small and moderate amplitudes agrees well with linear and weakly non‐linear perturbation theories, (iii) large amplitude oscillations compare well with some numerical and experimental published results.