Modular alkyl growth in amines via the selective insertion of alkynes into C–C bonds

The site-specific modification of amines has been a highly sought-after objective in organic synthesis. Despite the rapid advancement of carbon–hydrogen (C–H) bond functionalization methods, effective strategies for carbon–carbon (C–C) bond functionalization of amines remain elusive. Here we report a borane-catalysed method for the selective insertion of alkynes into alkyl C–C bonds of amines, resulting in the ring expansion of cyclic amines and chain elongation of acyclic amines. This approach begins with the cleavage of C–H bonds in amines, then transitioning to C–C bond functionalization upon reaction with alkynes. This method is effective with amines lacking an activating or leaving group and is suitable for late-stage functionalization of pharmaceuticals through C–C bond modification. Furthermore, by coupling this reaction with hydrolysis and hydrogenation steps, successive alkyne insertions are achieved, enabling modular and iterative alkyl growth of amines.