322,966 research outputs found
Absolute Configuration of Natural Products by Quantum Mechanical Calculation of Chiroptical Spectra
No full textCatalytic Asymmetric Oxidation of Aryl Methyl Sulfides Mediated by a (S,S)-Diphenylethane-1,2-diol/Titanium/Water Complex
No full textThe asymmetric oxidation of aryl methyl sulfides to sulfoxides with hydroperoxides has been achieved using catalytic amounts of the complex formed in situ between Ti(i-PrO)4, (S,S)-diphenylethan- 1,2-diol 1 and water. The sulfoxides are obtained in 60% yield and 67-80% enantiomeric excess
Asymmetric addition of dimethylzinc to malonates: a new synthetic strategy to valuable fragrances
No full textASYMMETRIC ADDITION OF DIMETHYLZINC TO MALONATES: A NEW SYNTHETIC STRATEGY TO VALUABLE FRAGRANCES
P. Scafato, V. Marchitiello, L. Pisani, S. Superchi, C. Rosini
Dipartimento di Chimica, Università degli Studi della Basilicata, via N. Sauro, 85; Potenza.
e-mail: [email protected]
The copper-catalyzed conjugate addition of organozinc reagent to α,β-unsaturated carbonyl compounds is a widely used strategy for the catalytic asymmetric C-C bond formation, with a large spectrum of substrates.1 Unfortunately, acyclic esters are not reactive in this reaction, in spite of the remarkable importance of chiral 3-alkylsubstituted esters both in asymmetric synthesis and as precursor of biologically active compounds. Recently, an efficient addition of dimethylzinc to unsaturated malonates, which can easily be transformed in monoesters by dealkoxycarbonylation, has been set up.2
We report herein the asymmetric addition of dimethylzinc to 3-phenylpropyliden malonate as a new route for the preparation of the valuable fragrances,3 Phenoxanol, Citralis and Nitrile Citralis, in optically active form.
References:
1) a) Feringa, B.L. Acc. Chem. Res. 2000, 33, 346. b) Alexakis, A.; Benhaim, C. Eur J. Org. Chem, 2002, 3221.
2) Schuppan, J.; Minnaard, A. J.; Feringa, B. L. Chem. Comm. 2004, 792.
3) Matteoli, U.; Ciappa, A.; Bovo,S.; Bertoldini, M.; Scrivanti, A. Tetrahedron:Asymmetry. 2007, 18, 797
Synthesis, characterization and application of new amphiphilic compounds as precursors of functional materials
No full textIn the last two decades or so, bile acids and their synthetic derivatives have been shown to be useful building blocks in the preparation of particular nanostructures in a bottom-up approach. This work is part of that research field and focused on the preparation of new derivatives of bile acids and on the study of their properties that make them versatile in a wide range of research field, from medicinal chemistry and catalysis to surface chemistry and molecular electronics.
In particular, this research work dealt with the synthesis of new aromatic derivatives through click reactions, an innovative synthetic method never described in literature to link aromatic subunits to bile acids, in order to evaluate their aggregation properties and the possibility of exploiting this functionalization method on this type of substrate. This is what will be shown in Chapter 2.
In Chapter 3, bile acids were then tested also as useful surfactants essential for amino acids catalytic activity carried out in only water.
Furthermore, in Chapter 4, from the positive data of the aforementioned tests arose the idea of directly functionalizing these amphiphilic molecules with amino acid subunits, also evaluating if this could give a greater contribution by increasing yields, diastereoisomeric and enantiomeric excesses, given the intrinsic characteristics of molecules capable of inducing higher stereoselectivity.
Finally, ferrocenyl derivatives were synthesized, connecting the subunits in C-3 position or on steroid skeleton side chain in order to obtain molecules capable of functionalizing graphene surfaces, deposited on electrodes, in order to prevent their oxidation while still allowing the ET and more generally molecules useful in molecular electronics. This was described in the final Chapter
Electrical and mechanical anharmonicities from NIR-VCD spectra of compounds exhibiting axial and planar chirality: The cases of (S)-2,3-pentadiene and methyl-d(3) (R)- and (S)-[2.2]paracyclophane-4-carboxylate.
No full textThe IR and Near infrared (NIR) vibrational circular dichroism (VCD) spectra of
molecules endowed with noncentral chirality have been investigated. Data for fundamental,
first, and second overtone regions of (S)-2,3-pentadiene, exhibiting axial chirality, and methyl-d3
(R)- and (S)-[2.2]paracyclophane-4-carboxylate, exhibiting planar chirality have been measured
and analyzed. The analysis of NIR and IR VCD spectra was based on the local-mode model and
the use of density functional theory (DFT), providing mechanical and electrical anharmonic
terms for all CH-bonds. The comparison of experimental and calculated spectra is satisfactory
and allows one to monitor fine details in the asymmetric charge distribution in the molecules:
these details consist in the harmonic frequencies, in the principal anharmonicity constants, in
both the atomic polar and axial tensors and in their first and second derivatives with respect to
the CH-stretching coordinates
Absolute configuration sensing of chiral aryl-and aryloxy-propionic acids by biphenyl chiroptical probes
No full textThe absolute configuration of chiral 2-aryl and 2-aryloxy propionic acids, which are among the most common chiral environmental pollutants, has been readily and reliably established by either electronic circular dichroism spectroscopy or optical rotation measurements employing suitably designed 4,4′-disubstituted biphenyl probes. In fact, the 4,4′-biphenyl substitution gives rise to a red shift of the diagnostic electronic circular dichroism signal of the biphenyl A band employed for the configuration assignment, removing its overlap with other interfering dichroic bands and allowing its clear sign identification. The largest A band red shift, and thus the most reliable results, are obtained by employing as a probe the 4,4′-dinitro substituted biphenylazepine 3c. The method was applied to the absolute configuration assignment of 2-arylpropionic acids ibuprofen (1a), naproxen (1b), ketoprofen (1c) and flurbiprofen (1d), as well as to the 2-aryloxypropionic acids 2-phenoxypropionic acid (2a) and 2-naphthoxypropionic acid (2b). This approach, allowing us to reveal the sample’s absolute configuration by simple optical rotation measurements, is potentially applicable to online analyses of both the enantiomeric composition and absolute configuration of these chiral pollutants
L'IMPIEGO DI VERRI DUROC SU SCROFE DI RAZZA PURA E INCROCIATE: EFFETTI SULL'EFFICIENZA RIPRODUTTIVA
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Regioselective Ortho-Alkylation of N,N-Diethylbenzamides via Lithiation and Copper Transmetalation Procedure
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