缺电子的硼烷催化的硅烷对CO的还原遵循一种反常理的机制,其中Si在羰基氧原子对硅原子的亲核攻击之前,H键被硼路易斯酸激活。如此形成的硼氢化物是实际的还原剂。这些步骤是通过使用硅立体异构硅烷进行阐明的,但是由于硅原子的消旋作用,将相同的技术应用于相关的CN基团的还原尚无定论。本研究现在通过我们的轴向手性硼烷催化剂和轴向手性硅烷试剂(两种对映体形式)的有意结合证明,这些氢甲硅烷基化的机理基本相同。硼烷/硅烷对的明确立体化学结果表明,两者均参与确定对映选择性的氢化物转移步骤。在发现我们的轴向手性碳原子团之后,这些实验成为可能6 F 5取代的硼烷在亚胺氢化硅烷化中诱导相当水平的对映体诱导。
Steric effects in palladium-catalysed amination of aryl triflates and nonaflates with the primary amines PhCH(R)NH2 (R=H, Me)
作者:Rebecca E. Meadows、Simon Woodward
DOI:10.1016/j.tet.2007.11.074
日期:2008.2
A systematic study of the effects of aryl triflate and nonaflate structure on the yield of amination with the primary amines PhCH(R)NH2 (R=H, Me) under palladium catalysis has been carried out. High throughput screening indicated that a catalyst composed of X-Phos/Pd-2(dba)(3)/1.4-dioxane was optimal based on a model reaction of Ar(ORf) [R-f-T-f (SO2CF3) Nf (SO2(CF2)(3)CF3)] with PhCH2NH2. Comparisons of the reactivity of various ArOTf and ArONf [Ar=4-MePh, 2-naphthyl, 1-naphthyl, 2-PhC6H4] indicated that both ortho substitution in the aryl electrophile and at the alpha-position on the amine are detrimental to the coupling particularly when they occur in combination. Despite being formally a monodentate ligand use of X-Phos leads to only small degrees of racemisation when using (R)-PhCH(Me)NH2 (typically resulting in a reduction from 97 to 86-94% ee for the amine stereocentre). (c) 2007 Elsevier Ltd. All rights reserved.
Illuminating the Mechanism of the Borane-Catalyzed Hydrosilylation of Imines with Both an Axially Chiral Borane and Silane
作者:Marius Mewald、Martin Oestreich
DOI:10.1002/chem.201202693
日期:2012.10.29
mechanisms of these hydrosilylations are essentially identical. Unmistakable stereochemical outcomes for the borane/silane pairs show that both participate in the enantioselectivity‐determining hydride‐transfer step. These experiments became possible after the discovery that our axially chiral C6F5‐substituted borane induces appreciable levels of enantioinduction in the imine hydrosilylation.
缺电子的硼烷催化的硅烷对CO的还原遵循一种反常理的机制,其中Si在羰基氧原子对硅原子的亲核攻击之前,H键被硼路易斯酸激活。如此形成的硼氢化物是实际的还原剂。这些步骤是通过使用硅立体异构硅烷进行阐明的,但是由于硅原子的消旋作用,将相同的技术应用于相关的CN基团的还原尚无定论。本研究现在通过我们的轴向手性硼烷催化剂和轴向手性硅烷试剂(两种对映体形式)的有意结合证明,这些氢甲硅烷基化的机理基本相同。硼烷/硅烷对的明确立体化学结果表明,两者均参与确定对映选择性的氢化物转移步骤。在发现我们的轴向手性碳原子团之后,这些实验成为可能6 F 5取代的硼烷在亚胺氢化硅烷化中诱导相当水平的对映体诱导。