Reviewing the energy profile of the F-cation transfer catalysis mechanism, the nucleophilic attack on Int-1 by ethyl diazoacetate (3) is the rate-determining step with an overall barrier of 19.4 kcal mol -1 , a value entirely reasonable for a reaction that proceeds rapidly at room temperature. Furthermore, the F-cation transfer catalysis mechanism (Figure ) accounts for the observed formation of racemic product when in situ synthesised optically active Nfluorinated (DHQD)2-PHAL catalyst was employed (Scheme 1c) . This lends further strong support to the plausibility of the mechanism, as outlined in Figure . Additionally, the ability of catalyst 1 to act as a F-cation transfer agent correctly predicts the observed preference for cis rather than trans stereochemistry associated with the racemic N-arylaziridine product. TS-2-trans, producing the trans-aziridine, is 1.4 kcal mol -1 higher than that of TS-2-cis; this is consistent with the experimental observation of cisaziridine as the major product, albeit with some degree of underestimation (see Figure and Figure in SI).