The Atropo-Enantioselective Reduction of Configurationally Unstable Biaryl Hydroxy Aldehydes - A Novel Approach to Axially Chiral Biaryls
作者:Gerhard Bringmann、Matthias Breuning
DOI:10.1055/s-1998-1728
日期:1998.6
The oxazaborolidine-assisted atropo-enantioselective catecholborane reduction of configurationally unstable biaryl hydroxy aldehydes to axially chiral biaryl alcohols by (dynamic) kinetic resolution is achieved in enantiomeric ratios (er) of up to 92:8. Using the same chiral auxiliary, the M- or, optionally, the P-configurated atropisomer can be obtained in good er's - just by variation of the relative quantity of the achiral reductant. This hints at the existence of two competing reaction pathways with opposite asymmetric inductions. The enantiomeric ratios observed strongly depend on the relative steric demand of the substituents ortho to the biaryl axis.
在噁唑硼烷辅助下,通过(动态)动力学解析将构型不稳定的双芳基羟基醛还原成轴向手性双芳基醇的邻苯二酚硼烷对映体选择性还原,对映体比(er)可达 92:8。使用相同的手性助剂,只需改变非手性还原剂的相对数量,就能以较好的对映体比(er's)获得 M-或 P-配置的异构体。这表明存在着两种具有相反不对称诱导作用的竞争反应途径。观察到的对映体比率在很大程度上取决于双芳基轴正向取代基的相对立体需求。