New and Expeditious Tandem Sequence Aza-Michael/Intramolecular Nucleophilic Substitution Route to Substituted γ-Lactams: Synthesis of the Tricyclic Core of (±)-Martinellines

A new and highly diastereoselective tandem reaction aza-Michael/intramolecular nucleophilic substitution is presented. This unprecedented tandem reaction between N-substituted α-bromoacetamides and Michael acceptors proceeds with good yields and excellent diastereoselectivity to provide the corresponding trisubstituted γ-lactam systems. An application to the concise synthesis of the tricyclic core of (±)-martinelline alkaloids is also described.