Pd- and Cu-Cocatalyzed Anaerobic Olefin Aminoboration

The established conditions for the oxidative aminoboration
of α-olefins
employ O2, a combustion accelerator, as the terminal oxidant.
Herein, we report an efficient Pd- and Cu-cocatalyzed aminoboration
of unactivated olefins, employing benzoquinone as the terminal oxidant.
These conditions allow for enhanced turnover frequencies and an improved
substrate scope relative to those of other Pd-catalyzed aminoboration
reactions. These highly practical, selective, and high-yielding aminoboration
conditions overcome many of the challenges associated with ligand-free
oxidative Pd catalysis. The representative scope of the reaction includes
50 examples. α-Olefins, internal vinyl arenes, and strained
cyclic olefins all participate along with a wide variety of amine
nucleophiles. Mechanistic investigations support the idea that the
rapid rate of oxidation by benzoquinone and Cu(II) prevents the aggregation
of heterogeneous Pd(0) species, allowing the Pd to remain homogeneous
throughout the aminoboration reaction. The scalability of the reaction
and the synthetic utility of the products are demonstrated.