Stereoselective Addition of Racemic Allenylzinc onto Enantiopure N-tert-Butanesulfinimines

Significance

The authors recently reported the synthesis of enantiopure trans-ethynylaziridines by the stereoselective addition of racemic allenyl­zinc to enantiopure N-tert-butanesulfinimines. In this paper they discovered that the addition of 60 equivalents of HMPA to the reaction reversed the stereoselection to give predominantly cis-ethynyl­aziridines.

The high cis-stereoselectivity was postulated to result from a kinetic resolution of the allenes via a synclinal transition state in either a supra- or antarafacial S_E2′ process. Semiempirical AM1 and MM2 calculations supported this theory.