Asymmetric Synthesis of 𝜸-Borylated Amines via Rhodium-Catalyzed Hydroboration of Allylamine Derivatives

Authors

Rukshani Wickrama Arachchi, University of Nebraska-LincolnFollow
Shekhar KC, University of Nebraska-Lincoln
Arun Suneja, University of Nebraska-Lincoln
James Takacs, University of Nebraska-Lincoln

Date of this Version

Spring 4-11-2022

Document Type

Article

Comments

Copyright © 2022 by the authors

Abstract

The Takacs group has explored different dimensions of Catalytic Asymmetric Hydroboration (CAHB) reaction mainly focusing on variety of amide, oxime ether and phosphonate directing groups. Inspired by the results obtained with BINOL- and TADDOL- derived chiral catalysts along with pinacolborane, we explored the potential of acyclic N-acyl allylamines as substrates for direct-hydroboration to prepare chiral amine derivatives bearing g-boronic ester functionality, yields up to 90% with 98:2 enantioselectivity. The major enantiomer obtained is independent of starting alkene geometry, revealing that rhodium-catalyzed cis/trans-alkene isomerization occurs prior to hydroboration. In this poster, we will discuss the generation of active catalysts starting from different pre-catalysts. We find that the counterion (e.g., BF₄^-, BArF^-) plays an important role in the reaction. Furthermore, we find that the addition of an external fluoride source (e.g., tetrabutylammonium difluorotriphenylsilicate (TBAT)) significantly impacts the reaction rate. These and other observations lead us to consider a novel catalytic cycle initiated by a rhodium(I)-hydride complex. Finally, the stereospecific transformations of the newly generated C–B bond to access drug candidates will be highlighted to demonstrate the utility of these chiral synthons.