BICAAC‐Catalyzed Hydroboration of N‐Heteroarenes and Imines: A Metal‐Free Route to Reduced N‐Heterocycles and Amines

ABSTRACT

Catalytic hydroboration of N‐heteroarenes and imines represents an attractive and sustainable strategy for accessing a broad range of synthetically valuable nitrogen‐containing compounds. Herein, we disclose the metal‐free catalytic activity of bicyclic (alkyl)(amino)carbene (BICAAC) ( I ) toward the hydroboration of N‐heteroarenes and imines using pinacolborane (HBpin). The catalyst exhibits excellent regioselectivity, promoting 1,4‐hydroboration of pyridines and 1,2‐hydroboration of quinolines, while efficiently reducing a variety of imines under mild reaction conditions. Mechanistic investigations, based on a series of control experiments, reveal that the reaction is initiated by the addition of the B─H bond of HBpin across the carbene center to generate the catalytically active BICAAC‐borane species ( II ). This intermediate activates the substrate through a Lewis acid–base interaction between the boron center and the nitrogen atom of the substrate, followed by hydride transfer from a second equivalent of HBpin to afford the hydroborated products. This work significantly expands the scope of BICAAC organocatalysis and demonstrates its potential as an efficient metal‐free catalyst for the reduction of challenging nitrogen‐containing unsaturated substrates.