- Structural optimization of enantiopure 2-cyclialkylamino-2-aryl-1,1- diphenylethanols as catalytic ligands for enantioselective additions to aldehydes
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(Chemical Equation Presented) The structural optimization of a family of modular, enantiopure β-amino alcohol ligands with a common 2-amino-2-aryl-1,1-diphenylethanol skeleton, whose stereogenicity was introduced through the Jacobsen epoxidation of 1,1-diphenyl-2-arylethylenes, has led to the identification of a small set of optimal catalysts with enhanced activity and enantioselectivity in the addition of alkylzinc and arylzinc reagents to aldehydes. Criteria for the discrimination between apparently analogous, highly enantioselective ligands are proposed.
- Rodriguez-Escrich, Sergi,Reddy, Katamreddy Subba,Jimeno, Ciril,Colet, Gisela,Rodriguez-Escrich, Carles,Sola, Lluis,Vidal-Ferran, Anton,Pericas, Miquel A.
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p. 5340 - 5353
(2008/12/20)
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- A superior, readily available enantiopure ligand for the catalytic enantioselective addition of diethylzinc to a-substituted aldehydes
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The lithium perchlorate-induced ring opening of (S)-triphenylethylene oxide (3) with secondary amines (piperidine (a), N-methylpiperazine (b), AT-phenylpiperazine (c) and morpholine (d)) takes place in a stereospecific and completely regioselective manner to afford CR)-2-(dialkylamino)-l, 1, 2-triphenylethanols (4a-d). These amino alcohols catalytically induce the addition of diethylzinc to benzaldehyde with high enantioselectivity at 0 °C and at room temperature. Ligand 4a, which provides the highest enantioselectivity at 0 °C, has been studied in the addition of Et2Zn to a family of 20 representative aliphatic and aromatic aldehydes 5a-t. For a 17-membered set of a-substituted substrates (5a-m, q-t), including ortho-, meta-, and para-substituted benzaldehydes, the naphthaldehydes, ct./i?-unsaturated and aliphatic (cyclic and acyclic) aldehydes, the mean enantiomeric excess of the resulting alcohols 6a-m, q-t is 97%, whereas for three a-unsubstituted specimens (5n-p) the addition takes place with an enantioselectivity of 92-93%.
- Sola, Lluis,Reddy, Katamreddy Subba,Vidal-Ferran, Anton,Moyano, Albert,Pericàs, Miquel A.,Riera, Antoni,Alvarez-Larena, Angel,Piniella, Joan-F.
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p. 7078 - 7082
(2007/10/03)
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