To gain more insight into the formation of 3a at the expense of the expected bicyclic 4a, Density Functional Theory (DFT) calculations were carried out at the dispersion-corrected SMD(CH2Cl2)-B3LYP-D3/def2-SVP level (see computational details in the Supporting Information). Figure shows the computed rection profiles leading to the formation of the 3a and 4a from the corresponding free aziridinium ylides, which according to our previous calculations on related systems, 20b,21 derives from the nucleophilic addition of the aziridine 2a to the Rh2-carbene intermediate (formed upon reaction of the diazo-compound and Rh2(OAc)4).