NHC-catalyzed [4 + 2] annulation of 2-bromo-2-enals with acylhydrazones: enantioselective synthesis of δ-lactams.

An asymmetric assembly of δ-lactams was realized via the NHC-catalyzed formal [4 + 2] annulation of acylhydrazones and 2-bromo-2-enals bearing γ-H. The advantages of this protocol include high enantioselectivity, good yields, mild reaction conditions and potential biological significance of the final products.