The residue was resuspended in i-PrOH (1 mL, 0.2 M) and stirred at 40 °C for 4 h (or until a single diastereomer was present by 1 H NMR), and then concentrated under reduced pressure. The resulting product was suspended in dry THF (500 μL, 0.4 M) and stirred at RT for 2 min prior to the dropwise addition of LiHMDS (0.26 mmol, 1.3 equiv). The reaction was stirred at RT for 30 min, quenched with saturated NH4Cl solution, and extracted with EtOAc. The combined organic layers were dried over Na2SO4, filtered, and concentrated under reduced pressure. The crude product was purified by column chromatography (silica gel, 0-5% EtOAc in hexane) to yield the desired cis-aziridine 12 as a yellow oil (25 mg, 48%). Calculations employed the MN15 density functional and the 6-31+G** basis set. 15 Solvation was incorporated via the SMD continuum solvation model. All geometries were optimised and confirmed as minima or transition states by frequency calculation in Gaussian16. Free energies were computed with the goodvibes software with concentration of 1M, temperature of 298 K and a frequency cutoff of 20 cm -1 and the Grimme quasi-harmonic approach for low frequency vibrations. Systematic conformational sampling of all minima was undertaken with low energy conformations subjected to redundant internal coordinate scanning to obtain corresponding transition states. Electrostatic potential was computed in GaussView using default settings and molecular structure visualizations created in CYLview2.