Bond-Weakening Catalysis: Conjugate Aminations Enabled by the Soft Homolysis of Strong N–H Bonds
摘要:
The ability of redox-active metal centers to weaken the bonds in associated ligands is well precedented, but has rarely been utilized as a mechanism of substrate activation in catalysis. Here we,describe a catalytic bond-weakening protocol for conjugate amination wherein the strong N-H bonds in N-aryl amides (N-H bond dissociation free energies similar to 100 kcal/mol) are destabilized by similar to 33 kcal/mol upon by coordination to a reducing titanocene complex, enabling their abstraction by the weak H-atom acceptor TEMPO through a proton-coupled electron transfer process. Significantly, this soft homolysis mechanism provides a method to generate closed-shell, metalated nucleophiles under neutral conditions in the absence of a Bronsted base.
Practical Synthesis of Allylic Silanes from Allylic Esters and Carbamates by Stereoselective Copper-Catalyzed Allylic Substitution Reactions
作者:Martin Oestreich、Gertrud Auer
DOI:10.1002/adsc.200404381
日期:2005.4
The first copper-catalyzedallylic substitution reactions of allylic acetates and carbamates employing a bis(triorganosilyl)zinc reagent are reported. This novel procedure avoids the use of stoichiometric amounts of copper salts which are usually mandatory with this chemistry. Application of this methodology to standard model substrates substantiates a high diastereoselectivity for the double bond