Stereoselective double lewis acid/organo-catalyzed dimerization of donor-acceptor cyclopropanes into substituted 2-oxabicyclo[3.3.0]octanes

A new approach for the dimerization of donor-acceptor cyclopropanes (2-arylcyclopropane-1,1-dicarboxylates) under double-catalysis conditions by treatment with 20 mol % of GaCl(3) and dimethyl 3,5-dimethyl-1-pyrazoline-3,5-dicarboxylate as a specific organocatalyst has been found. Under these conditions, the starting compounds are regio- and stereospecifically converted into polysubstituted 2-oxabicyclo[3.3.0]octanes. Two new rings, one C-O bond, and two C-C bonds are formed in this process, and four stereocenters are thus created. The reaction mechanism was thoroughly studied by NMR spectroscopy, and a number of intermediates were detected.     

Nickel(0)/NaHMDS adduct-mediated intramolecular alkylation of unactivated arenes via a homolytic aromatic substitution mechanism

A variety of polycycles can be synthesized via an intramolecular alkylation cyclization promoted by Ni(PPh(3))(4) and NaHMDS. Mechanistic investigations support the catalytic nature of Ni(0) in the course of TEMPO scavenging experiments and its association with the substrate and NaHMDS to form an adduct by DOSY NMR.     

Intramolecularly Coordinated Organotin Tellurides: Stable or Unstable?

The step-wise oxidation of an organotin(I) compound with elemental tellurium gave a variety of unprecedented organotin tellurides containing tin atoms in the oxidation states +II and +IV.     

Synthesis of diversely 1,3,5-trisubstituted pyrazoles via 5-exo-dig cyclization

5-Exo-dig cyclocondensation of alk-3-yn-1-ones with hydrazines, in the presence of montmorillonite K-10, provides an effective method with a high atom economy for the synthesis of diversely 1,3,5-trisubstituted pyrazoles. The microwave-accelerated reaction proceeds in the absence of solvent and leads to 5-benzyl substituted pyrazoles with good yields (72-91%). The regiochemistry of the process was confirmed by the X-ray crystallographic structure determination of 1-(2-fluorophenyl)-5-(4-methylbenzyl)-3-phenyl-1H-pyrazole.     

Stable water and glycerol marbles immersed in organic liquids: from liquid marbles to Pickering-like emulsions

Water and glycerol marbles coated with various powders and immersed in organic liquids gave rise to water-in-oil and glycerol-in-oil Pickering-like emulsions. Non-polar oils such as polydimethylsiloxane, toluene, xylenes and chlorinated solvents supported the formation of emulsions, whereas polar liquids such as dimethylsulfoxide, N,N,-dimethylformamide, acetone and ethanol did not. It is demonstrated that there is a direct contact between a liquid filling the immersed marble and the surrounding liquid. A phenomenological theory of the marbles' sinking into emulsion is proposed.     

Monomeric organoantimony(III) sulphide and selenide with terminal Sb-E bond (E = S, Se). Synthesis, structure and theoretical consideration

NCN chelated monomeric chalcogenides, LSbE (E = S (1), Se (2), L = 2,6-bis[N-(2',6'-dimethylphenyl)ketimino]phenyl), were synthesized and characterized with the help of elemental analysis, NMR spectroscopy and single-crystal X-ray diffraction analyses. The terminal Sb-E (E = S, Se) bonds in 1 and 2 were subjected to theoretical investigation and the results are compared with the hypothetical molecules, PhSb=E (E = S, Se, Te), and earlier reported analogues.     

Different morphologies of the dry physical gels as a function of the sample preparation method

Xerogels obtained by drying the gels formed by glucofuranose derivatives with organic solvents were studied. The xerogels were characterized using the SEM, XRD, DSC and OPM techniques. The morphology of a xerogel observed by SEM may change from ‘amorphous, fibrillar’ to ‘crystal-like’, which may be caused by time or temperature. The results suggest that a similar transition may take place when the xerogel is being prepared. Thus SEM pictures of xerogels should be treated with great caution as they may not reflect the gelator network morphology in the bulk gel.     

Transformation of diamond to graphite under heat treatment at low pressure

Diamond is a very persistent metastable form of carbon. At low pressure, graphitization of the diamond surface is observed at temperatures lower than 1700 °C. The basic cause of this is known to be interaction with oxygen. In the present paper, the microphysics of the phenomenon of diamond surface graphitization was studied. It has been shown that surface graphitization proceeds in several stages. First, a thin surface layer of graphite is developed due to interaction with oxygen (and probably other substances). As temperature is increased, nuclei of 5–10 nm in size are formed within it. The graphite nuclei are capable of migrating along the surface of diamond. They form ‘nests,’ where they are coalesced into aggregates 10–100 nm in size. These ‘nests’ give rise to diamond surface layer graphitization, which proceeds along diamond {211} crystallographic planes and forms graphitization figures. At this stage, the factor that determines the transformation is the pressure exerted on graphitizing material by the surrounding diamond.     

The lock-in and reorientational phase transitions in metallic superlattices

We show that in the metallic magnetic superlattices, along with the bilinear RKKY-like exchange, there is significant biquadratic contribution arising from intrinsic and fluctuational mechanisms. Within the phenomenological approach, we postulate a particular form of free energy density functional and study the thermodynamic behaviour of the system under consideration. The model permits a transparent interpretation of the phase transitions, observed in metallic multilayers, with multiple oscillation periods and biquadratic exchange effects taken into account.     

Enthalpy difference between conformations of normal alkanes: effects of basis set and chain length on intramolecular basis set superposition error

The quantum chemistry of conformation equilibrium is a field where great accuracy (better than 100?cal?mol^?1) is needed because the energy difference between molecular conformers rarely exceeds 1000–3000?cal?mol^?1. The conformation equilibrium of straight-chain (normal) alkanes is of particular interest and importance for modern chemistry. In this paper, an extra error source for high-quality ab initio (first principles) and DFT calculations of the conformation equilibrium of normal alkanes, namely the intramolecular basis set superposition error (BSSE), is discussed. In contrast to out-of-plane vibrations in benzene molecules, diffuse functions on carbon and hydrogen atoms were found to greatly reduce the relative BSSE of n-alkanes. The corrections due to the intramolecular BSSE were found to be almost identical for the MP2, MP4, and CCSD(T) levels of theory. Their cancelation is expected when CCSD(T)/CBS (CBS, complete basis set) energies are evaluated by addition schemes. For larger normal alkanes (N?>?12), the magnitude of the BSSE correction was found to be up to three times larger than the relative stability of the conformer; in this case, the basis set superposition error led to a two orders of magnitude difference in conformer abundance. No error cancelation due to the basis set superposition was found. A comparison with amino acid, peptide, and protein data was provided.