A synthetic approach to the functionalized hydroazulene core of guanacastepenes and heptemerenes

A functionalized hydroazulene derivative has been synthesized efficiently from 2-methylcyclopent-2-en-1-one as a part of a study oriented toward the total synthesis of diterpenoids of biological significance, guanacastepenes, and heptemerones.     

Dressed energy of the XXZ chain in the complex plane

We highlight what seems to be a remaining subtlety in the argument for the cancellation of the total anomaly associated with the M5-brane in M-theory. Then, we prove that this subtlety is resolved under the hypothesis that the C-field flux is charge-quantized in the generalized cohomology theory called J-twisted cohomotopy.

     

A convenient synthesis of deuterium labeled tertiary aliphatic nitro ketones and nitriles - starting materials for preparation of deuterated cyclic nitrones, isomeric hydroxylamines, and corresponding C-nitroso compounds

Tertiary aliphatic β- and γ-nitro nitriles and ketones deuterated in (several) selected positions had been synthesized. The deuterated nitro compounds served as a starting material for the corresponding deuterium labeled nitrones or hydroxylamines (reducing with aluminum amalgam). Further oxidation of the last two groups of compounds with sodium periodate or m-CPBA afforded the relevant deuterated tertiary C-nitroso compounds.     

2-Substituted nitrones and isomeric hydroxylamines - obtained via aluminium amalgam reduction of nitro nitriles and ketones—a new access to convenient intermediates for nitroso carbonyl compounds preparation

Substituted five-membered cyclic nitrones (pyrroline N-oxides) have been obtained in good to high yields from tertiary γ-nitro ketones and nitriles employing aluminium amalgam as a reducing agent in moist diethyl ether or THF. Attempts to obtain cyclic amino nitrones from α- or β-nitro nitriles failed and only the corresponding hydroxylamines have been isolated. Both nitrones and hydroxylamines have been used for synthesis of tertiary C-nitroso nitriles or ketones.     

Ruthenium catalysts bearing chelating carboxylate ligands: application to metathesis reactions in water

The novel catalytic system, composed of a ruthenium alkylidene containing a surfactant fragment in the catalysts molecule, is reported. Ring closing metathesis and cross metathesis reactions proceed efficiently in neat water at room temperature, in air, without need of adding an external surfactant.     

The effect of meteorological parameters on radon concentration in borehole air and water

Seasonal and short term variations of ²²²Rn activity concentration in borehole air and water of the borehole drilled in cracked quartzite were studied and possible response on meteorological parameters was examined. Seasonal change of radon concentration in borehole air due to atmospheric temperature was confirmed. Short term variation of radon concentration in borehole air coincided with the atmospheric pressure changes. The strong impact of rainfall on radon concentration values was observed both in air and water environments. The decrease of radon content in borehole air and water followed radioactive decay law exclusively in spring and summer month. Contrary to borehole water, rainfall increased radon concentration in borehole air during spring and summer months only. In this paper the results from two and half years of investigation are presented.     

Construction of the tricyclic 5-7-6 scaffold of fungi-derived diterpenoids. Total synthesis of (±)-heptemerone G and an approach to Danishefsky's intermediate for guanacastepene A synthesis

An efficient and operationally simple synthesis of the neodolestane diterpenoids (±)-heptemerone G and (±)-guanacastepene A is reported. The common tricyclic scaffold (±)-4 was prepared from 2-methylcyclopent-2-en-1-one via 23 isolated intermediates in 5.1% yield. The key features include a novel annulation sequence combining tandem conjugate addition, methylenation, and metathesis reaction and completely diastereoselective transformation of the azulene derivative 23 into rings AB building block 32. Stereochemistry of alkylation of both saturated trans-azulene enolate 38 and its α,β-unsaturated counterpart 48 was examined. Rather surprisingly, a different facial selectivity was recorded. Several synthetic methods were modified or developed, including an alternative methodology for the Wharton-type rearrangement, ketalization of epimerizable ketone under mild conditions, and efficient alkylation of a ketone via its kinetic enolate.     

Trap-assisted tunnelling current in MIM structures

A new model is presented of current transport in Metal Insulator Metal (MIM) structures by quantum mechanical tunnelling. In addition to direct tunnelling through an insulating layer, tunnelling via defects present in the insulating layer plays an important role. Examples of the influence of the material and thickness of the insulating layer, energy distribution of traps, and metal work functions are also provided.     

TiO2 thick films supported on reticulated macroporous Al2O3 foams and their photoactivity in phenol mineralization

TiO₂ thick films deposited on macroporous reticulated Al₂O₃ foams with pore size of 10 ppi and 15 ppi were prepared using dip coating from slurries of Aeroxide^® P25 nanopowder and precipitated titania. All prepared films have sufficiently good adhesion to the surface of the substrate also in case of strongly cracked films. No measurable release of deposited TiO₂ after repeated photocatalytic cycles was observed. The photocatalytic activity was characterized as the rate of mineralization of aqueous phenol solution under irradiation of UVA light by TOC technique. The best activity was obtained with Aeroxide^® P25 coated Al₂O₃ foam with the pore size of 10 ppi, annealed at 600 °C. The optimal annealing temperature for preparation of films from precipitated titania could be determined at 700 °C. Films prepared by sol-gel deposition technique were considerably thinner compared to coatings made of suspensions and their photocatalytic activity was significantly smaller.