1,721,455 research outputs found
L'insegnamento dell'epidemiologia a livello universitario. Atti 40° Congresso Nazionale SItI. Cernobbio, 8-11 settembre 2002. Panorama della Sanità 2002;
No full textA safe and mild synthesis of organic carbonates from alkyl halides and tetrabutylammonium alkyl carbonates
No full textA safe and mild procedure for the synthesis of
mixed organic carbonates is described. Reaction of com-
mercially available tetrabutylammonium methoxide and
ethoxide with carbon dioxide yields the corresponding meth-
yl and ethyl tetrabutylammonium carbonates (TBAMC and
TBAEC). The reactions of these new compounds with several
different alkyl halides give methyl and ethyl carbonates in
high yields. The use of classic toxic and harmful chemicals
such as phosgene and carbon monoxide is avoided
Electrochemically induced diastereoselective functionalization of N-acyloxazolidin-2-ones
No full textThe electrochemical generation of chiral enolates is here described,
either by cathodic reduction of a C-Br bond or using electrogenerated
acetonitrile anion. The reactivity of these enolates have been studied in
carboxylation, alkylation and conjugate addiction reactions, obtaining in
some cases a good diastereoselectivity
Theoretical–Computational Modeling of CD Spectra of Aqueous Monosaccharides by Means of Molecular Dynamics Simulations and Perturbed Matrix Method
Full text linkThe electronic circular dichroism (ECD) spectra of aqueous d-glucose and d-galactose were modeled using a theoretical–computational approach combining molecular dynamics (MD) simulations and perturbed matrix method (PMM) calculations, hereafter termed MD-PMM. The experimental spectra were reproduced with a satisfactory accuracy, confirming the good performances of MD-PMM in modeling different spectral features in complex atomic–molecular systems, as already reported in previous studies. The underlying strategy of the method was to perform a preliminary long timescale MD simulation of the chromophore followed by the extraction of the relevant conformations through essential dynamics analysis. On this (limited) number of relevant conformations, the ECD spectrum was calculated via the PMM approach. This study showed that MD-PMM was able to reproduce the essential features of the ECD spectrum (i.e., the position, the intensity, and the shape of the bands) of d-glucose and d-galactose while avoiding the rather computationally expensive aspects, which were demonstrated to be important for the final outcome, such as (i) the use of a large number of chromophore conformations; (ii) the inclusion of quantum vibronic coupling; and (iii) the inclusion of explicit solvent molecules interacting with the chromophore atoms within the chromophore itself (e.g., via hydrogen bonds)
Investing in epidemiological surveillance for recovering health systems in war-torn countries
No full textSynthesis of Nitrogen-Containing Heterocyclic Scaffolds through Sequential Reactions of Aminoalkynes with Carbonyls
Full text linkSequential reactions of aminoalkynes represent a powerful tool to easily assembly biologically important polyfunctionalized nitrogen heterocyclic scaffolds. Metal catalysis often plays a key role in terms of selectivity, efficiency, atom economy, and green chemistry of these sequential approaches. This review examines the existing literature on the applications of reactions of aminoalkynes with carbonyls, which are emerging for their synthetic potential. Aspects concerning the features of the starting reagents, the catalytic systems, alternative reaction conditions, pathways and possible intermediates are provided
Electrochemically-initiated Michael addition of chiral acetoacetic derivatives to methyl vinyl ketone: stereocontrolled construction of quaternary carbon centers
No full textStereoselective conjugate addition of chiral -dicarbonyl derivatives to methyl vinyl ketone was promoted by electrolysis, using a catalytic amount of electricity. With respect to the metal-catalyzed methods, the electrochemical, metal-free conditions resulted in enhanced reactivity of the electrogenerated enolates, so that the Michael addition was found to occur under mild conditions and short reaction times, affording products with significant diastereoisomeric excesses. When Oppolzer’s sultam was used as the chiral inductor and prolonged reaction times were employed, a reversal in the stereoselectivity was observed, evidencing kinetic control in the electrochemically-induced addition and subsequent thermodynamic equilibration. The electro- chemically-based method was also exploited for the elaboration of quaternary stereogenic carbon centers
- …
