The reaction with nitromethylbenzene 2l indicates a competition between denitration and electron transfer to FMNsq under the reaction conditions. To better understand the distinctive feature of this reaction, we conducted density functional theory (DFT) calculations on the model reaction (Fig. ) and the one involving nitromethylbenzene 2l (Supplementary Fig. ). We found the initial addition step of α-amidyl radical Int-1 to nitronate 5 is occurring rapidly with a free energy barrier of only 9.9 kcal mol -1 for the model reaction. The resulting radical anion Int-2 readily undergoes irreversible denitration (a free energy barrier of 9.6 kcal mol -1 ) to give the radical Int-3, which is terminated by HAT from FMNsq, as supported by deuterium labeling experiments (Supplementary Fig. ), to provide the final product 3a (Fig. ). Next, the same DFT calculations were conducted with nitromethylbenzene 2l (Supplementary Fig. ). While a similar free energy barrier (10.0 kcal mol -1 ) was observed for the initial addition step, we found a higher energy barrier (13.4 kcal mol -1 ) for the denitration step, indicating a slower denitration step when compared to the model reaction with 2a. Thus, as a competitive pathway to the desired cross-coupling, the radical anion Int-2' can be terminated by oxidation by FMNsq to provide product 40 (Supplementary Fig. ).