Controlling product outcomes with temperature. Changing the carbene precursor to the CNcontaining diazoketone 2c provided the first example of divergence between dehydromorpholine 4c and the [3,9]-aziridine 3c. Standard reaction conditions furnished 3c in 68% yield (by NMR), accompanied by 19% of the dehydromorpholine 4c (Scheme 3A, right). This 3.6:1 ratio of 3c:4c led us to employ computations to probe whether an NCI was also present in the corresponding aziridinium ylide and to estimate the barrier to C-N bond rotation. Computational analysis confirmed the presence of an NCI, where the O•••C(=O) distance of INT4 is predicted to be 2.619 Å (Scheme 3B compared to 2.530 Å, Figure ), with a stabilizing interaction energy of E = 4.44 kcal/mol. The balance between the computed barrier to C-N bond rotation between INT3 and INT4 of 12.5 kcal/mol and the presence of an NCI leads to a divergent reaction where both 3c and 4c are accessible. These computational observations are reflected in the calculated reaction profile (Scheme 3B), where both the activation energy barriers leading to 3c and 4c are accessible (G ≠ ⁓8.5 kcal/mol), but slightly higher than that of 3a (Figure , vide supra). This higher barrier to C-N bond rotation (compared to the analogous ylide INT2) is likely a result of charge delocalization across the CN group (as compared to the ketone in INT2); nonetheless, it is still low enough to ultimately give rise to the product distribution based on temperature.