Bromamine-T as an efficient amine source for Sharpless asymmetric aminohydroxylation of olefins

Asymmetric aminohydroxylation of various olefins was carried out using bromamine-T as nitrogen source in the presence of (DHQ)₂PHAL ligand. The new nitrogen source has been found to be effective in terms of yield and reaction time. The optical purities of the products could be obtained with up to 99% ee.     

Chlorotrimethylsilane catalyzed synthesis of 1,3-diphenyl-2-propenones and their antimicrobial activities

The base- or acid-catalyzed Claisen–Schmidt condensation reaction is the common synthetic route for the synthesis of 1,3-diphenyl-2-propenone (known as chalcone). A variety of different synthetic pathways have been used over the decades in the synthesis of chalcone. Microwave irradiation in absence of solvent is employed successfully and presented here with prominent improvement over the existing methods. The reaction is incredibly accelerated in the presence of the catalyst chlorotrimethylsilane (CTMS) and found superior in terms of reaction time, product yield, safer synthetic route, and easy removal of catalyst etc. Products were characterized by elemental analysis and spectroscopy. Single crystal X-ray diffraction was used to determine crystal structures. All compounds were treated for antimicrobial activity. The profound response against bacteria and fungus pathogens by these compounds is impressive and opens up opportunities for further physiological activity studies.     

Changes in electrical properties in α- and γ-exposed PADC track detector

The changes in the dielectric properties and temperature dependence of the d.c. conductivity of α-exposed poly allyl diglycol carbonate (PADC) have been studied. On α-irradiation the dielectric constant (′) as a function of frequency has been found to decrease significantly. The temperature dependence of resistivity in pristine and γ-irradiated samples is of the form ρ(T)=ρ_∝ exp(T₀/T) which can be attributed to conduction of thermally generated carriers. In case of (γ+α) irradiated samples the temperature dependence of resistivity is of the form ρ(T)=ρ_∝ exp(T₀/T)^1/2 which is due to one-dimensional hopping of carriers.     

Photon transport in thin disordered slabs

We examine using Monte Carlo simulations, photon transport in optically ‘thin’ slabs whose thickness L is only a few times the transport mean free path l*, with particles of different scattering anisotropies. The confined geometry causes an auto-selection of only photons with looping paths to remain within the slab. The results of the Monte Carlo simulations are borne out by our analytical treatment that incorporates directional persistence by the use of the Ornstein-Uhlenbeck process, which interpolates between the short time ballistic and long time diffusive regimes.     

Ultra-low-frequency dust-electromagnetic modes in self-gravitating magnetized dusty plasmas

Obliquely propagating altra-low-frequency dust-electromagnetic waves in a self-gravitating, warm, magnetized, two fluid dusty plasma system have been investigated. Two special cases, namely, dust-Alfvén mode propagating parallel to the external magnetic field and dustmagnetosonic mode propagating perpendicular to the external magnetic field have also been considered. It has been shown that effects of self-gravitational field, dust fluid temperature, and obliqueness significantly modify the dispersion properties of these ultra-low-frequency dust-electromagnetic modes. It is also found that in parallel propagating dust-Alfvén mode these effects play no role, but in obliquely propagating dust-Alfvén mode or perpendicular propagating dust-magnetosonic mode the effect of self-gravitational field plays destabilizing role whereas the effect of dust/ion fluid temperature plays stabilizing role.     

Do carbenes have a "hidden" carbon(0) character? Revisiting the electronic structure of 2,2'-bipyridyl carbene

Density functional calculations predict that 2,2'-bipyridyl carbenes have some degree of "hidden" carbon(0) character. This is supported by very high second proton affinity values and bond dissociation energies (BDEs) for the dissociation of one AuCl and one Ni(CO)(2) molecule from [(AuCl)(2)(2,2'-bipyridyl carbene)] and [{Ni(CO)(2)}(2)(2,2'-bipyridyl carbene)]. An Arduengo type carbene also showed significant BDE values for gem-dimetallation, thus indicating the possible existence of carbon(0) character. All of the dimetallated derivatives showed metallophilic interactions.     

Metal‐Only Lewis Pairs by Reversible Insertion of Ruthenium and Osmium Fragments into Metal–Boron Double Bonds

New metal‐only Lewis pairs (MOLPs: Ru→Cr and Os→Cr) are prepared by the insertion of a zerovalent ruthenium or osmium complex into chromium–boron double bonds of borylene complexes. The reaction creates new borylene complexes (the first ever for osmium), and is crystallization‐controlled; re‐dissolving the complexes results in regeneration of the starting materials. A mechanism is proposed based on DFT calculations, along with a computational study of the unusual MOLPs.     

Rapid access to homoallylic alcohols via Pd(OAc)2 catalyzed Barbier type allylation in presence of DMAP

DMAP was found to accelerate significantly the rate of Pd(OAc)₂ catalyzed Barbier type allylation of carbonyl compounds by allylbromide using SnCl₂·2H₂O as reducing agent. Both aldehyde as well as ketones produced excellent yields within a short reaction time in the presence of 3 mol % of Pd(OAc)₂ and 12 mol % of DMAP at room temperature. Aldehydes could be allylated within 5–10 min whereas, in case of ketones, the reaction completes in 45–120 min.     

Chemoselective Transfer Hydrogenation of Carbonyl Compounds Catalyzed by Macrocyclic Nickel (II)Complex

Macrocyclic Ni(II) complex, 1, catalyzes efficiently the chemoselective transfer reduction of carbonyl compounds in presence of propan-2-ol / KOH or HCO₂H / HCO₂NH₄ as hydrogen donors to produce the corresponding alcohols in high yield.