High kinetic resolution in the addition of a racemic allenylzinc onto enantiopure N-tert-butanesulfinimines:: Concise synthesis of enantiopure trans-2-ethynylaziridines

Enantiopure trans-ethynyl N-tert-butanesulfinylaziridines (R-s)-6 were prepared in good to excellent yields by the condensation of the racemic allenylzinc species 1 derived from 3-chloro-l-trimethyl-silylpropyne onto the corresponding enantiopure N-tert-butanesulfinimines (R-s)-5. The absolute stereochemistry of enantiopure N-tert-butanesulfinylaziridines (R-s)-6 was shown to be (R-s,2R,3R) and results from a chelate-type transition state in which the zinc atom of allenylzinc 1 is coordinated by both the nitogen and the oxygen atoms of the imine. Further removal of the N-tert-butanesulfinyl auxiliary of alkyl 3-substituted and 3,3-disubstituted ethynyl N-tert-butanesulfinylaziridines (Rs)-6 could be achieved by treatment with HCl in MeOH affording the corresponding deprotected aziridines (2R,3R)-9 and (2R)-9 respectively as enantiomerically pure compounds.