Based on our computational analysis of [3,9]-aziridine formation in Figure kcal/mol to rotation about the C-N bond (black line). The reaction of 1 with 2b revealed a higher barrier of 12 kcal/mol (green line) for C-N bond rotation. In contrast, aziridinium ylides formed from reaction of 1 with dicarbonyl-containing diazo compounds 2e and 2f show significantly higher barriers to rotation around the C-N bond at ~23 kcal/mol (red line), and 20 kcal/mol (blue line), respectively. This increased rotational barrier may be attributed to the ability of the enolate of the ylide to be delocalized over both carbonyl-containing groups, providing additional structural rigidity and steric bulk that hinders the C-N bond rotation.