Stereoselective Lewis Acid Mediated (3+2) Cycloadditions of N-H- and N-Sulfonylaziridines with Heterocumulenes

Alkyl and aryl isothiocyanates and carbodiimides are effective substrates in (3+2) cycloadditions with N‐sulfonyl‐2‐substituted aziridines and 2‐phenylaziridine for the synthesis of iminothiazolidines and iminoimidazolidines. Additionally, the stereoselective (3+2) cycloaddition of N‐H‐ and N‐sulfonylaziridines with isothiocyanates can be accomplished, allowing for the synthesis of highly enantioenriched iminothiazolidines. Evidence for an intimate ion‐pair mechanism is presented herein in the context of these chemo‐, regio‐, and diastereoselective transformations. The demonstrated ability to remove the sulfonyl group from the heterocyclic products displays the utility of these compounds for further derivatization and application. Coordinate, release, and expand: A Lewis acid coordinated process by which the release of strain energy drives the ring expansion of aziridines to five‐membered heterocycles through a stereoselective (3+2) cycloaddition with alkyl and aryl isothiocyanates and carbodiimides is presented. These zinc(II)‐mediated reactions exhibit broad substrate scope, high yields, and well‐defined chemo‐ and regioselectivity.