Catalytic Radical Approach for Selective Carbene Transfers via Cobalt(II)‐Based Metalloradical Catalysis

Radical reactions have been increasingly explored as new tools for organic synthesis as they exhibit unique features, including fast reaction rate and high functional group tolerance. Despite tremendous endeavors, long-standing challenges associated with control of reactivity and selectivity, especially enantioselectivity, have remained unaddressed for many radical reactions. Among recent advances, metalloradical catalysis (MRC) has emerged as a conceptually different approach for achieving the control of reactivity and stereoselectivity in radical processes through the use of metalloradicals for catalytic generation of metal-stabilized organic radicals. To this end, cobalt(II) complexes of porphyrins [Co(Por)], as stable metalloradicals, have been shown to exhibit unique capability for homolytic activation of diazo compounds to generate the fundamentally new α-Co(III)-alkyl radicals as key intermediates for MRC. Through the support of porphyrin ligands with tunable electronic, steric, and chiral environments, the Co(II)-based MRC has been successfully applied for the development of various radical processes for selective carbene transfers.