Diastereoselective Palladium-Catalyzed (3+2)-Cycloadditions from Cyclic Imines and Vinyl Aziridines

The synthesis of cyclic imidazolidines via two N-C bond-forming sequences has been developed. The transformation goes through a (3 + 2)-cycloaddition reaction in the presence of catalytic amounts of palladium by combining several vinyl aziridines and cyclic N-sulfonyl imines. Interestingly, the use of LiCl as additive allowed the improvement of diastereoselectivities when less encumbered substrates were used. The imidazolidine derivatives that bear aminal cores are isolated in high yields (15 examples, up to 96% yield) and diastereoselectivities (up to >20:1).