Copper-Mediated Dehydrogenative C(sp3)–H Borylation of Alkanes

Borylations of inert carbon–hydrogen bonds are highly useful for transforming feedstock chemicals into versatile organoboron reagents. Catalysis of these reactions has historically relied on precious-metal complexes, which promote dehydrogenative borylations with diboron reagents under oxidant-free conditions. Recently, photoinduced radical-mediated borylations involving hydrogen atom transfer pathways have emerged as attractive alternatives because they provide complimentary regioselectivities and proceed under metal-free conditions. However, these net oxidative processes require stoichiometric oxidants and therefore cannot compete with the high atom economy of their precious-metal-catalyzed counterparts. Herein, we report that CuCl2 catalyzes radical-mediated, dehydrogenative C(sp3)–H borylations of alkanes with bis(catecholato)diboron under oxidant-free conditions. This is a result of an unexpected dual role of the copper catalyst, which promotes oxidation of the diboron reagent to generate an electrophilic bis-boryloxide that acts as an effective borylating agent in subsequent redox-neutral photocatalytic C–H borylations.