Catalytic Enantioselective Preparation of α,β-Unsaturated δ-Lactams

Significance

The aza-Diels-Alder reaction of Brassard’s diene 1 with imines represents one of the most convenient approaches to chiral α,β-unsaturated δ-lactams, which can be converted into a number of biologically important compounds. However, thus far only one example on catalytic enantioselective aza-Diels-Alder reaction of 1 with imines mediated by a chiral Brønsted acid was ­reported (Angew. Chem. Int. Ed. 2006, 45, 4796). In this paper Feng’s group describes a catalytic enantioselective protocol employing the ytterbium complex of chiral N,N′-dioxide ligand 2. A number of α,β-unsaturated δ-lactams were obtained in moderate yields (30-58%) and good enantioselectivities (59-81% ee); the transformation was accomplished in two steps via Mannich-type intermediates.