Iodocyclization/base-induced hydrodeiodination reaction of 5-substituted 4-alkenols. The influence of substituent on the stereoselective pathway

The electrophilic iodocyclization reaction of (Z)- and (E)-5-n-alkylsubstituted 4-alken-1-ols followed by base-induced hydrodeiodination reaction stereoselectively gave, respectively, (Z)- and (E)-alkylidentetrahydrofurans in high yield. Completely different outcomes were observed with (Z)- and (E)-6,6-dimethylhept-4-en-1-ol: their iodocyclization furnished, respectively, threo- and erythro-2-(1-iodo-2,2-dimetylpropyl)tetrahydrofuran with high stereoselectivity. The threo isomer gave clean formation of 6-tert-butyl-3,4-dihydro-2H-pyran by base-induced ring expansion, while erythro isomer underwent a base-induced ring contraction to 1-cyclopropyl-3,3-dimethylbutan-1-one. Moreover, (Z)- and (E)-5-cyclopropylpent-4-en-1-ol underwent a 6-endo-iodocyclization to threo- and erythro-2-cyclopropyl-3-iodotetrahydro-2H-pyran, respectively, that under the same basic treatment, gave two isomeric 6-cyclopropyldihydro-2H-pyrans in a stereoselective fashion.     

A first theoretical study on the origin of the metal-mediated regioselective opening of 2,3-epoxy alcohols

Hybrid density functional theory (B3LYP) method allows the study of the role of metal ions (Li(+)) in the regioselective opening of 2,3-epoxy alcohols with lithium halides (Cl, Br, I) to the corresponding halohydrins. The theoretical results largely confirm the experimental results, especially with regards to the regioselectivity observed in the opening of the oxirane ring. The C3 halogen attack is always preferred to the C2 attack, with a significant difference in the TS structures with the reaction pathway under kinetic control. The central role of the lithium cation, linked to the oxygen atoms of the epoxy alcohol, is well documented in the reaction mechanisms presented. The energy differences between the two structures of the proposed TS appear to be ascribed to the different contribution of the X-H-O hydrogen bond between the hydroxyl groups of the reactant and the incoming halogen nucleophile.     

Stereocontrolled Transformations of trans α,β‐Aziridine Aldehydes toward Different Amino Hydroxylated Structures

The stereocontrolled condensation of methyl ketones to trans α,β‐aziridine aldehydes creates functionalized aldols, valuable precursors for different amino hydroxylated structures, such as amino alcohols, amino diols, α‐tetrahydrofuryl amides, and α‐furyl amides.     

Carbon and nitrogen distribution in the sediments of lagoon of Ravenna (Italy)

The distribution and the origin of carbon and nitrogen in sediments of an Italian lagoon--located north-east of Ravenna town--were investigated. From 1957 to 1976, the lagoon had been affected by a strong industrial pollution due to an important petrochemical complex. At present, industrial and domestic waste waters undergo a treatment process before being discharged into the lagoon. Sediment samples from 10 locations throughout the lagoon were analysed, in order to document the spatial and vertical distribution of C and N. Data show a very strong variability (organic carbon content varies between 8.9% and 0.14%) and the highest values were found in the immediate vicinity of the industrial discharge. Sediment organic matter shows allochthonous origin in proximity of industrial discharge and autochthonous origin in the remaining areas.     

Domino processes as a tool for recovering substandard reactions. Synthesis and use of nitroacetic acid esters and amides

[reaction: see text] Elusive nitroacetic acid esters and amides were obtained through a halogen exchange reaction of the corresponding bromoacetic acid derivatives with polymer-supported nitrite anion. The process is flawed by a side product catalyzed degradation of the products. Domino processes turned out to be a powerful tool for overcoming such drawbacks, converting a substandard reaction into an efficient multicomponent preparation of 4-hydroxy-4,5-dihydroisoxazoles.     

Aspect-ratio dependent oscillatory thermocapillary convection in the floating half zone

The dependency of the critical Marangoni number on the geometrical aspect ratio of the floating half zone is essential to predict the onset of oscillatory thermocapillary convection.The experimental studies in the microgravity conditions on floating half zones of several centimeters in diameter have predicted that the critical Marangoni number increases with the increasing aspect ratio,and the terrestrial experimental studies have predicted the contradictory conclusion for floating half zones of several mil...     

Non-Gravitational Effects with Density-Matching in Evaluating the Influence of Sedimentation on Colloidal Coagulation

The method of density matching between the solid and liquid phases is often adopted to effectively eliminate the effect of sedimentation of suspensions in studies on dynamic behaviour of a colloidal system. However, the associated changes in the solvent composition may bring side effects to the properties investigated and therefore might lead to a faulty conclusion if the relevant correction is not made. To illustrate the importance of this side effect, we present an example of the sedimentation influence on the coagulation rate of suspensions of 2μm （diameter） polystyrene. The liquid mixtures, in the proper proportions of water （H2O）, deuterium oxide （D2O） and methanol （MeOH） as the liquid phase, density-matched and unmatched experiments are performed. Besides the influence of viscosity, the presence of methanol in solvent media, used to enhance the sedimentation effect, causes significant changes （reduction） in rapid coagulation rates compared to that in pure water. Without the relevant corrections for those non-gravitational factors it seems that gravitational sedimentation would retard the coagulation. The magnitude of the contribution from the non-gravitational factor is quantitatively determined, making the relevant correction possible. After necessary the influence of the sedimentation on coagulation rates at corrections for all factors, our experiments show that the initial stage of the coagulation is not observable.