256 research outputs found
Flexible Biphenyls as CD Probes for Assignment of the Absolute Configuration of 2-Arylpropionic Acids
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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
Biphenyl dioxolanes as circular dichroism probes for the assignment of absolute configuration to aliphatic diols: Extending the scope to anti 1,n-diols and cyclic syn 1,2-diols
No full textWe describe herein the use of a flexible biphenyl moiety as efficient chirality probe in the assignment of the absolute configuration (AC) of aliphatic, non-chromophoric diols. The diols are transformed in the corresponding biphenyl dioxolanes in which the biphenyl system has either a P or M torsion depending on the chirality of the diol. As the correlation between biphenyl torsion and diol AC has been established and the sense of torsion is revealed by the sign of the biphenyl A band at 250 nm in the CD spectrum of the dioxolane, then the diols AC can be assigned simply looking at the CD spectra of these derivatives. This approach proved to be general, straightforward, and reliable for anti 1,2- 1,3-, and 1,4-diols bearing both one and two stereogenic centers and for cyclic syn 1,2-diol
Catalytic 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
From enantioselective catalysis to stereochemical assignments: a continuous journey through organic stereochemistry
No full text1,1’-Binaphthylazepine-based ligands for the enantioselective dialkylzinc addition to aromatic aldehydes
No full textThe new 1,1′-binaphthylazepine ligand 1c has been prepared and tested in the enantioselective addition of Et2Zn to arylaldehydes, allowing us to reach ee's up to 97% and giving extremely rapid reactions (10-20 min). Aminoalcohol 1c and the analogous compounds 1a and 1b were then tested in the enantioselective addition of Bu2Zn and Me2Zn to arylaldehydes. All of the ligands efficiently catalyze the Bu2Zn addition to benzaldehyde, providing good yields in short reaction times (2-4 h) and high ee (up to 96%). In the enantioselective methylation of arylaldehydes ligands 1b and 1c gave high yields (88-97%) and good to high (80-90%) ee'
Ossidazione Asimmetrica Catalitica di Solfuri a Solfossidi Mediante Complessi di Titanio con 1,2-Diaril-1,2-etandioli
No full textEnantioselective Phenylation and Alkynylation of Aromatic Aldehydes Promoted by 1,1’-Binaphthylazepine-based Aminoalcohols
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