A practical o-hydroxybenzylamines promoted enantioselective addition of dialkylzincs to aldehydes with asymmetric amplification
摘要:
The addition of dialkylzincs to aldehydes is accelerated considerably by the presence of a catalytic amount of o-hydroxybenzylamine (R,R)-2e to give, after hydrolysis, the corresponding alcohol (S)-9 in good enantiomeric purity. The origins of the enantioselection have been elucidated. A strong positive nonlinear relationship was observed for the reaction enantioselectivity with the use of o-hydroxybenzylamine 2e, which is very accessible through a short stereoselective synthetic route. The enantiomeric purity of the product 9 is much higher than the d.e. of the chiral source 2e, and the rate of the enantioselective catalysis increases considerably with the increase of the d.e. of(R,R)-2e. (C) 2000 Elsevier Science Ltd. All rights reserved.
Synthesis of Enantiopureo-Hydroxybenzylamines by Stereoselective Reduction of 2-Imidoylphenols: Application in the Catalytic Enantioselective Addition of Diethylzinc to Aldehydes
o-hydroxybenzylamines 2a–i were synthesized by diastereoselective reduction of the 2-imidoylphenols (R)-1a–i. Conformational analysis enabled the assignment of the absolute configurations of compounds 2a–i. The accessible o-hydroxybenzylamine (R,R)-2h serves as an effective catalyst precursor for highly enantioselectiveaddition of diethylzinc to aliphatic and aromatic aldehydes. This pathway represents a practical