A Superior, Readily Available Enantiopure Ligand for the Catalytic Enantioselective Addition of Diethylzinc to α-Substituted Aldehydes
- 11 September 1998
- journal article
- Published by American Chemical Society (ACS) in The Journal of Organic Chemistry
- Vol. 63 (20) , 7078-7082
- https://doi.org/10.1021/jo981336i
Abstract
The lithium perchlorate-induced ring opening of (S)-triphenylethylene oxide (3) with secondary amines (piperidine (a), N-methylpiperazine (b), N-phenylpiperazine (c) and morpholine (d)) takes place in a stereospecific and completely regioselective manner to afford (R)-2-(dialkylamino)-1,1,2-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 α-substituted substrates (5a − m,q−t), including ortho-, meta-, and para-substituted benzaldehydes, the naphthaldehydes, α,β-unsaturated and aliphatic (cyclic and acyclic) aldehydes, the mean enantiomeric excess of the resulting alcohols 6a − m,q − t is 97%, whereas for three α-unsubstituted specimens (5n − p) the addition takes place with an enantioselectivity of 92−93%.Keywords
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