Stereoselective Syntheses of Highly Functionalized Imidazolidines and Oxazolidines via Ring-Opening Cyclization of Activated Aziridines and Epoxides with Amines and Aldehydes

A mild one-pot stereospecific synthetic route to highly
functionalized
imidazolidines and oxazolidines via SN2-type ring-opening
of the corresponding activated aziridines and epoxides with amines
followed by p-toluenesulfonic acid (PTSA)-catalyzed
intramolecular cyclization with aldehydes has been developed. The
methodology tolerates a variety of functional groups and furnishes
the desired products in high yields (up to 92%) with excellent stereoselectivities
(de, ee > 99%). Interestingly, imidazolidines were formed as the
cis-isomers,
whereas oxazolidines were produced as trans-isomers exclusively.