Diasteroselective synthesis of oxazolidines and imidazolidines via the Lewis acid catalyzed C-C cleavage of aziridines

In this work, cis-2,5-disubstitutedoxazolidines were efficiently constructed via a regioselective C-C bond cleavage of N-tosylaziridine 2,2-dicaboxylates and a subsequent 3+2] cycloaddition with aromatic aldehydes in the presence of Zn(OTf)₂. The reactions were highly diastereoselective to form oxazolidines in cis configurations. trans-2,5-Disubstituted imidazolidines were also diastereoselectively synthesized in the similar manner using imines as substrates and AgOTf as catalyst. Based on the detailed investigation of the substrate diversity for both reactions, including the electronic effects and the steric effects of the substituted groups on the aziridines, aldehydes, and imines, a stepwise mechanism was postulated for the diastereoselective formation of cis-2,5-disubstitutedoxazolidines and trans-2,5-disubstituted imidazolines.