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

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.