Ligand-Controlled Asymmetric Induction at a Transition Metal-Bonded α-Carbon in Ester and Amide Enolates. Diastereoselective Formation of Oxapalladacycles Applied to the Synthesis of a Chiral Nonracemic 2<i>H</i>-1-Benzopyran
作者:Janelle L. Portscheller、Sara E. Lilley、Helena C. Malinakova
DOI:10.1021/om030207b
日期:2003.7.1
diastereomeric excess 46−80% exploiting asymmetric induction from the chiral ligands. The stereoselective event involved an intramolecular displacement of the iodide in complexes (P−P)IPd-1-C6H4-2-OCH2Y by an in situ generated lithium or potassium ester or amide enolate. Only one enantiomer of each ligand was used, and the absolute sense of stereoinduction could be controlled by the choice of the base (t-BuOK
具有手性非外消旋双齿膦膦配体的稳定苯甲酰氧杂四环[-(P-P)Pd-1-C 6 H 4 -2-OCHY-],(P-P)=(4 S,5 S)-(+)- O -异亚丙基-2,3-二羟基-1,4-双(二苯基膦基)丁烷((S,S)-DIOP)或(2 S,4 S)-(-)-2,4-双(二苯基膦基)戊烷( (S,S)-BDPP)和钯键结合的立体碳,代表酯(Y = COOEt)或酰胺(Y = CONEt 2)中的α-碳)烯醇盐,是利用手性配体的不对称诱导合成的,其对映体过量为46-80%。立体选择性事件涉及通过原位生成的锂或钾的酯或酰胺烯醇化物在配合物(P-P)IPd-1-C 6 H 4 -2-OCH 2 Y中碘化物的分子内置换。每个配体仅使用一种对映异构体,并且可以通过选择碱基(t- BuOK或LDA)来控制立体诱导的绝对意义,从而以非对映异构体富集的形式提供每个palladacycle的两种非对映异