β C–H di-halogenation via iterative hydrogen atom transfer
A radical relay strategy for mono- and di-halogenation (iodination, bromination, and chlorination) of sp3 C–H bonds has been developed. This first example of β C–H di-halogenation is achieved through sequential C–H abstraction by iterative, hydrogen atom transfer (HAT). A double C–H functionalization is enabled by in situ generated imidate radicals, which facilitate selective N˙ to C˙ radical translocation and tunable C–X termination. The versatile, geminal di-iodide products are further elaborated to β ketones and vinyl iodides. Mechanistic experiments explain the unique di-functionalization selectivity of this iterative HAT pathway, wherein the second C–H iodination is twice as fast as the first.