Copper-Catalyzed Aminoboration from Hydrazones To Generate Borylated Pyrazoles.

Herein we report an aminoboration reaction that employs inexpensive, Earth-abundant, and commercially available Cu(OTf)2 as an effective catalyst in the direct addition of B-N σ bonds to C-C π bonds, generating borylated pyrazoles, which are useful building blocks for drug discovery. By nature of the mechanism, the reaction produces exclusively one regioisomer and tolerates groups incompatible with alternative lithiation/borylation and iridium-catalyzed C-H activation/borylation methods. The reaction can be scaled up, and the resulting isolable pyrazole pinacol boronates can be further functionalized through palladium-catalyzed Suzuki cross-coupling reactions.