Cobalt-catalyzed HAT reaction for asymmetric hydrofunctionalization of alkenes and nucleophiles

The first-row transition-metal-catalyzed hydrogen atom transfer reaction has emerged as a practical synthetic platform for alkene hydrofunctionalization with high chemo- and regioselectivity. As a cheap and biocompatible 3d-metal catalyst, cobalt (Co) is one of the most widely studied catalysts and exhibits versatile catalytic activity in metal-hydride-mediated hydrogen atom transfer (MHAT) reactions. Alongside the alkene hydrofunctionalization reaction with various radicalophiles and electrophiles, the Co-catalyzed HAT reaction can also realize the coupling of alkenes with nucleophiles and provides opportunities for catalyst-controlled stereoselective transformations that were previously absent in MHAT catalysis. Mechanism demonstrates that the SN2-like displacement of the diastereomeric alkylcobalt(IV) intermediates with nucleophiles is the key for the new bond formation and conducive to the enantiocontrol. This perspective summarizes the recent emerging enantioselective development based on a Co-catalyzed HAT process for forging C−C and C−X bonds. We also highlight the challenges and opportunities faced by the MHAT reaction and emerging applications in enantioselective radical transformation.