Diastereoselective Synthesis of syn-β-Lactams Using Rh-Catalyzed Reductive Mannich-Type Reaction of α,β-Unsaturated Esters

The combination of Et2Zn and RhCl(PPh3)(3) led to the facile generation of a rhodium-hydride complex (Rh-H) that catalyzed the 1,4-reduction of alpha,beta-unsaturated esters. The resulting rhodium enolate performed as a Reformatskytype reagent and reacted with various imines to give syn-beta-lactams in good to excellent yields with high diastereoselectivity.