Ni-Catalyzed 1,1- and 1,3-Aminoboration of Unactivated Alkenes

Abstract

Alkene functionalization has evolved to become a resourceful approach to accessing more complex molecules, such as medicines. In particular, alkene borylamination reactions have been a valuable synthetic strategy in recent years due to the versatile C-N and C-B bonds afforded in the process. Although significant work has been done on 1,2-borylamination reactions, successful conditions for 1,1- and 1,3-borylamination of unactivated alkenes have not been reported. The present collaborative study introduces a Ni-catalyzed methodology for the 1,1-borylamination of disubstituted and mono-substituted alkenes and the 1,3-borylamination of cyclic alkenes. We explored the reaction mechanism of the latter using density functional theory (DFT) calculation, which unveiled the presence of a facile equilibrium between regioisomeric intermediates via sequential syn--hydride eliminations and re-insertion transition states (TSs). It also revealed the relevance of favorable non-covalent interactions between the ring’s substituents in the axial position for better stabilization. The calculations suggested that the reaction proceeds with close to barrierless oxidative addition, followed by facile reductive elimination. Together, these factors contribute to the favored regio- and stereoselectivity towards the major 1,3-borylamination product from cyclohexene, therefore supporting the experimental observations and results