Metal-Free Directed Site-Selective Csp -H Borylation of Saturated Cyclic Amines.

The borylation of Csp -H bonds is a challenging transformation that is typically restricted to transition metal catalysis. Herein, we report the site-selective metal-free Csp -H borylation of saturated cyclic amines. It is possible to selectively borylate piperidine derivatives at the α or β positions according to the reaction conditions. The mechanism was supported by NMR spectroscopy, calorimetry experiments and density functional theory (DFT) computations. It suggests that the piperidine is dehydrogenated by complexation with BBr to produce an enamine intermediate, which is in turn borylated at either the α or β position according to the reaction conditions.