Synthesis of Chiral Pyridylphenols for the Enantioselective Addition of Diethylzinc to Aldehydes
作者:Pei-Shan Wu、Chinpiao Chen
DOI:10.1002/jccs.201100474
日期:2012.6
Chiral 8‐substituted 2‐(8,10,10‐trimethyl‐6‐aza‐tricyclo[7.1.1.02,7]undeca‐2(7),3,5‐trien‐5‐yl)‐phenols were prepared from a high enantiopurity (>97% ee) of (1R)‐(+)‐α‐pinene, and assessed in the enantioselectiveaddition of diethylzinc to substituted benzaldehydes, giving the (S)‐alcohols with enantiomeric excess ranging from 33% to 89%. Interestingly, in all cases, except for those of ortho‐chlorobenzaldehyde
applicability as chiralcatalysts was evaluated by carrying out the same reaction on a family of aldehydes, including variously substituted aromatic ones as well as an aliphatic analogue. The results have confirmed the validity of the fine-tuning process performed on ligands 13a and 13b. In fact, both exhibited excellent catalytic activity as demonstrated by the chemical yields and ee obtainedfrom all the
Chiral Amplification Based on Enantioselective Dual-Phase Distribution of a Scalemic Bisoxazolidine Catalyst
作者:Shuanglong Liu、Christian Wolf
DOI:10.1021/ol070915j
日期:2007.8.1
A readily available bisoxazolidine ligand was found to catalyze the asymmetric alkylation of aldehydes with Et2Zn and less reactive Me2Zn, providing high yields and ee's in both reactions. The bisoxazolidine-catalyzed alkylations and alkynylation of benzaldehyde show a positive nonlinear effect that cannot be accounted for by Kagan's MLn model. The chiral amplification originates from selective phase distribution favoring enrichment of the major enantiomer of the scalemic catalyst in solution.