It is important to note that the success of this general phosphonylation protocol relies on the choice of 2-iodobenzoyl group as the intramolecular HAT reagent. Most reported hydrogen atom abstractors for the activation of C(sp 3 )-H bonds are electrophilic, 2a,20 which makes them reactive partner with commonly used phosphorous source in C-P bond formation reactions, such as radical addition to phosphite, 5a or HAT with dialkyl/aryl phosphite or dialkyl/aryl phosphine oxide which contain weak P-H bonds. The intramolecular 1,5-HAT process outcompetes the side reaction with phosphorus reagent (in this case, premature phosphonylation on aryl ring), leading to the successful generation of -aminoalkyl radicals with amines as the limiting reagent (see Supplementary Section S4.3). Meanwhile, the "oxidative" nature of the 2-iodobenzoyl group triggers an oxidative-quenching cycle of the excited photocatalyst, affording PC •+ , which enables the RPC pathway, rendering the final Arbuzov-type phosphonylation possible. Finally, the iodide released in the first step can act as a nucleophile to dealkylate intermediate D, delivering the desired -aminophosphonate without the need of an external nucleophile. 7b,12d All these factors worked synergistically and contributed to the success of this general, unique, and operationally simple phosphonylation method. Scheme 3. Synthetic applications and mechanistic studies.