1,721,020 research outputs found
1,1’-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'
Potentials, limits and challenges for the Fair Trade in Nepal: an overview of the perception by the members of the Fair Trade Group Nepal
No full textThis paper studies fair trade in Nepal, focusing on the views of Nepalese producers. The first chapter is an introduction on fair trade and the main global actors, the second chapter explains the context of this research and the methodology which has been used to collect information, the third chapter presents all data which has been collected and the final chapter draws the conclusions of this work
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 of Chiral Flavanones by Asymmetric Conjugate Addition
No full textChiral flavanones represent an important class of natural compounds, which are components of tomatoes, citrus fruits like grapefruits, oranges, lemons and some herbs such as mint1 and posses an impressive and varied array of biological and pharmacological properties, namely, anti-inflammatory, immunomodulatory, antiviral and anticarcinogenic activities.2
However, their potential applications as drugs are strongly limited by the expensive extractions from plant tissues that contain them; so their activity has been tested in most cases as racemic mixtures, in spite of the well known relationship between biological properties of chiral compounds and their absolute configuration.
In this communication we report the synthesis of some optically active flavanones, based on the asymmetric rhodium-catalyzed conjugate addition of arylboronic acid to chromones,3 in turn prepared by corresponding 2-hydroxy-acetophenones, which can occur with high enantioselectivity
A general method for the stereoselective synthesis of gamma and delta lactones and application to the preparation of natural optically active flavors and fragrances
No full textSynthetic approach toward cis-disubstituted γ- and δ-lactones through enantioselective dialkylzinc addition to aldehydes: application to the synthesis of optically active flavors and fragrances
No full textA versatile and straightforward approach to optically active cis-4,5-disubstituted g- and d-lactones by
catalytic enantioselective addition of dialkyzincs to cinnamic aldehydes and RCM ring closure has been
reported. The synthetic importance of the enantioselective dialkylzinc alkylation of aldehydes has been
thus widened. Such an approach has then been employed for the enantioselective synthesis of naturally
occurring g-lactone flavors like (S)-5-ethyl-butanolide (6a) and (4S,5S)-cis-whisky lactone (6b) and extended
to the preparation of d-lactones like (5S,6S)-5-methyl-6-ethylpentanolide (9a), precursor of the
pheromone serricorni
Synthesis of Chiral Phosphites and Their Application in the Asymmetric Addition of Dimethylzinc to Alkylidenmalonates
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