Sulfenate Anion Catalyzed Diastereoselective Synthesis of Aziridines

Aziridines are highly valued synthetic targets in organic and medicinal chemistry. The organocatalytic synthesis of such structures with broad substrate scope and good diastereoselectivity, however, is rare. Herein, we report a broadly applicable and diastereoselective synthetic method for the synthesis of trans-aziridines from imines and benzylic or alkyl halides utilizing sulfenate anions (PhSO- ) as the catalyst. Substrates bearing heterocyclic aromatic groups, alkyl, and electron-rich and electron-poor aryl groups were shown to be compatible with this method (33 examples), giving good yields and high diastereoselectivities (trans : cis >20 : 1). Further functionalization of aziridines containing cyclopropyl or cyclobutyl groups was achieved through ring-opening reactions, with a cyclobutyl-substituted norephedrine derivative obtained through a four-step synthesis. We offer a mechanistic proposal involving reversible addition of the deprotonated benzyl sulfoxide to the imine to explain the high trans-diastereoselectivity.