Taking the F out of FLP: Simple Lewis Acid–Base Pairs for Mild Reductions with Neutral Boranes via Borenium Ion Catalysis
摘要:
Discrete three-coordinate borenium salts 1c and 1d are accessed by cooperative Lewis acid-base pair-mediated heterolytic splitting of the B-H bond in pinacolborane by B(C6F5)(3)center dot DABCO and Ph3C+/DABCO, respectively. The resulting salts are competent catalysts in the reduction of a broad range of imines and can be generated in situ. Moreover, a mechanistic framework for borenium catalysis based on experimental evidence is proposed. The reaction is suggested to proceed by borenium activation of the imine substrate followed by counterintuitive hydride delivery from HBPin (with the assistance of DABCO) rather than from the HB(C6F5)(3)(-) anion, contrary to typical mechanisms of reduction in FLP systems.
Nickel-Catalyzed Reductive and Borylative Cleavage of Aromatic Carbon–Nitrogen Bonds in N-Aryl Amides and Carbamates
作者:Mamoru Tobisu、Keisuke Nakamura、Naoto Chatani
DOI:10.1021/ja501649a
日期:2014.4.16
The nickel-catalyzed reaction of N-aryl amides with hydroborane or diboron reagents resulted in the formation of the corresponding reduction or borylation products, respectively. Mechanistic studies revealed that these reactions proceeded via the activation of the C(aryl)-N bonds of simple, electronically neutral substrates and did not require the presence of an ortho directinggroup.