399042-97-8Relevant academic research and scientific papers
Illuminating the mechanism of the borane-catalyzed hydrosilylation of imines with both an axially chiral borane and silane
Mewald, Marius,Oestreich, Martin
, p. 14079 - 14084 (2013/01/15)
The reduction of C=O groups with silanes catalyzed by electron-deficient boranes follows a counterintuitive mechanism in which the Si-H bond is activated by the boron Lewis acid prior to nucleophilic attack of the carbonyl oxygen atom at the silicon atom. The borohydride thus formed is the actual reductant. These steps were elucidated by using a silicon-stereogenic silane, but applying the same technique to the related reduction of C=N groups was inconclusive due to racemization of the silicon atom. The present investigation now proves by the deliberate combination of our axially chiral borane catalyst and axially chiral silane reagents (in both enantiomeric forms) that the 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 C6F 5-substituted borane induces appreciable levels of enantioinduction in the imine hydrosilylation. Copyright
Steric effects in palladium-catalysed amination of aryl triflates and nonaflates with the primary amines PhCH(R)NH2 (R=H, Me)
Meadows, Rebecca E.,Woodward, Simon
, p. 1218 - 1224 (2008/09/18)
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/Pd2(dba)3/1,4-dioxane was optimal based on a model reaction of Ar(ORf) [Rf=Tf (SO2CF3), Nf (SO2(CF2)3CF3)] 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 α-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).
