We then examined the structure of the post-reaction product. Following the reaction using 1a-TFA as a starting material, 1 H NMR analysis of the crude product was conducted (Figure ). A singlet peak corresponding to the methyl group was detected, and its chemical shift aligned with the protonated form of 2ad prepared independently. Washing the crude mixture with saturated NaHCO3 aq. led to a peak shift toward a higher magnetic field, consistent with the chemical shift of the insertion product, 2ad (see Supporting Information, Section 3.6). Oxidative insertion of EDA into 1a-TFA is anticipated to produce 2ad with TFA protection in the form of pyridinium salt. However, the presence of such an intermediate was not definitively confirmed, possibly due to its unstable nature, leading to hydrolysis into pyridine, followed by protonation via EGA. Further mechanistic study was conducted through theoretical calculations based on density functional theory (DFT) and the coupled-cluster method (Figure ). First, the denitrogenation step was simulated. The computation indicated that 28.12 kcal mol -1 is required to directly form a carbene from EDA, suggesting that N2 release from EDA barely occurs under ambient conditions (Figure ). In contrast, the nucleophilic addition of EDA to the radical cation requires only 5 kcal mol -1 of energy, while the release of N2 from the EDA-bound radical cation species requires minimal energy (Figure .91 kcal/mol at DLPNO-CCSD and 0.10 kcal/mol at DFT). Therefore, it can be reasonably inferred that EDA reacts with radical cations species as a nucleophile, leading to subsequent N2 release. The calculations also revealed that EDA addition at the 2-position of the pyrrole ring is energetically favorable (Supporting Information, Section 4.4.1).