Department of Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
Org Lett. 2010 Oct 15;12(20):4612-5. doi: 10.1021/ol101932q.
TADDOL-derived phosphites and phosphoramidites are effective ligands for rhodium-catalyzed asymmetric hydroborations of β,γ-unsaturated amides, achieving up to 99% ee. However, the sense of stereoinduction, R or S, is surprisingly dependent on rather subtle features of the ligand. For example, catalysts employing a TADDOL phenylphosphite and those using the closely related N-methylaniline-derived phosphoramidite of the same configuration give opposite enantiomers of the product. Those derived from optical antipodes give the same product with virtually the same enantioselectivity as illustrated above. The different stereochemical outcomes may reflect fundamental differences in catalyst structure, reactivity, or reaction mechanism.
TADDOL 衍生的膦酸酯和亚磷酸酯是铑催化β,γ-不饱和酰胺不对称硼氢化反应的有效配体,最高可达到 99%的对映选择性。然而,手性诱导的立体化学,即 R 或 S,却惊人地取决于配体的细微特征。例如,采用 TADDOL 苯膦酸酯的催化剂和采用相同构型的密切相关的 N-甲基苯胺衍生的亚磷酸酯的催化剂,会得到产物的对映异构体。而采用光学对映体衍生的催化剂则得到具有几乎相同对映选择性的相同产物,如上文所述。不同的立体化学结果可能反映了催化剂结构、反应性或反应机制的根本差异。