Department of Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0304, USA.
J Am Chem Soc. 2010 Feb 17;132(6):1740-1. doi: 10.1021/ja908257x.
Rhodium-catalyzed hydroborations of trisubstituted alkenes are generally slow and often suffer from competing alkene isomerization. In contrast, the trisubstituted alkene moieties contained within the framework of a beta,gamma-unsaturated amide undergo facile reaction, perhaps facilitated by carbonyl directing effects and two-point binding of the substrate to the rhodium catalyst. Stereoisomeric substrates, for example, (E)- and (Z)-3, cleanly give rise to diastereomeric products, and thus the rhodium-catalyzed reaction is stereospecific. In addition, simple TADDOL-derived phenyl monophosphite ligands in combination with Rh(nbd)(2)BF(4) afford highly enantioselective catalysts (seven examples, 91-98% ee). These catalysts provide an alternative methodology to prepare Felkin or anti-Felkin acetate-aldol products and related derivatives that are obtainable from the intermediate chiral organoboranes.
铑催化的三取代烯烃的硼氢化反应通常较慢，并且常常受到竞争的烯烃异构化的影响。相比之下，β，γ-不饱和酰胺骨架内的三取代烯烃部分易于反应，这可能是由于羰基的导向效应和底物与铑催化剂的两点结合所致。立体异构底物，例如(E)-和(Z)-3，可以干净地生成非对映异构体产物，因此铑催化反应是立体专一的。此外，简单的 TADDOL 衍生的苯基单膦酸酯配体与 Rh(nbd)(2)BF(4)结合提供了高对映选择性的催化剂（七个实例，91-98%ee）。这些催化剂提供了一种替代方法来制备 Felkin 或反-Felkin 乙酸酯-aldol 产物和相关衍生物，这些产物可从中间手性有机硼烷获得。
