Lithiation-electrophilic trapping of N-sulfonyl-activated ethylene aziridines.

A detailed study on the lithiation-electrophilic trapping of N-sulfonyl ethylene aziridines is described. The optimum results required use of a N-2,4,6-tri-iso-propylbenzenesulfonyl activating group and lithiation using 3 equiv. of s-BuLi-PMDETA for 1 minute before addition of the electrophile. In situ trapping with Me3SiCl was also successful. Electrophilic trapping with aldehydes provided a stereoselective route to syn-hydroxy aziridines. Alternatively, keto aziridines could be stereoselectively reduced to syn-hydroxy aziridines using NaBH4-CeCl3. The relative stereochemistry in two of the hydroxy aziridines was established unequivocally by X-ray crystallography.