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 E 2′ process. Semiempirical AM1 and MM2 calculations supported this theory.